Forem: Devashish Roy

Understanding SOLID Principles — The Foundation of Better Software Design

Devashish Roy — Wed, 19 Nov 2025 19:26:47 +0000

I am currently working on the project YouTubeLayer. The prototype worked fine initially, but when I tried to move it to a working production system and scale it, everything started breaking. It felt like playing Jenga — touch one block, and the whole tower comes crashing down.

That’s when I stumbled upon something that completely changed the way I thought about software design — the SOLID principles.

These five principles aren’t just fancy theory; they’re a way of writing code that’s easy to understand, extend, and maintain. And trust me — once you start applying them, your code (and your sanity) will thank you.

Let’s go through them one by one, in the simplest way possible 👇

🧩 S — Single Responsibility Principle (SRP)

Definition:
A class should have only one reason to change — in other words, it should do only one thing.

In plain English:
Don’t make a “God class” that does everything — logging, sending emails, calculating bills, and making coffee.

Example:
I once worked on a UserManager class that handled both user authentication and sending email notifications. Every time we updated the notification logic — like changing email templates or adding a new notification type — the authentication system mysteriously broke. 😅

We eventually split it into two separate classes — AuthManager for authentication and NotificationManager for sending emails. After that, changes became smooth and predictable. It was such a relief!

Why it matters:
It makes debugging, testing, and updating code simpler and safer.

🚪 O — Open/Closed Principle (OCP)

Definition:
Classes should be open for extension but closed for modification.

In plain English:
You should be able to add new features without touching existing code.

Example:
This reminds me of a time when I had to add subscription payments to my platform. Initially, all the payment logic lived inside one giant if-else block — handling credit cards, UPI, and wallets all in one place. When I tried adding a new option like PayPal, I had to dive back into that messy code and risk breaking existing functionality.

Later, I refactored the system by introducing a base Payment interface and creating separate classes like CreditCardPayment, UPIPayment, and PayPalPayment. After that, adding a new payment mode was as simple as creating a new class — no need to touch the old code. It felt like magic ✨

Why it matters:
It keeps old features safe while allowing new features to be added easily.

🔄 L — Liskov Substitution Principle (LSP)

Definition:
Subclasses should be replaceable with their parent classes without breaking the application.

In plain English:
If a subclass can’t perform the same role as its parent, it shouldn’t be a subclass.

Example:
This happened when I designed a Payment interface for my subscription system with a processSubscription() method. I had different payment classes like CreditCardPayment, UPIPayment, and CashOnDelivery.

At first, I thought they could all just extend Payment, but then I realized — Cash on Delivery couldn’t actually process a subscription renewal automatically. When I passed a CashOnDelivery object where a regular Payment object was expected, the system broke because it couldn’t handle renewals properly.

Lesson learned — not every subclass should substitute its parent. Inheritance (or implementation) should make logical sense for the behavior it represents.

Why it matters:
It ensures consistency and prevents unexpected behavior when using inheritance or interfaces.

🧱 I — Interface Segregation Principle (ISP)

Definition:
Clients shouldn’t be forced to depend on interfaces they don’t use.

In plain English:
Don’t create one huge interface — break it down into smaller, more specific ones.

Example:
This reminds me of a project where we had a Notifier interface with methods like sendEmail(), sendSMS(), and sendPushNotification().

But not every notification service supported all of these. For example, EmailNotifier didn’t need sendSMS() or sendPushNotification.

So I refactored it into smaller interfaces — EmailNotifier, SMSNotifier, and PushNotifier. That way, each service only implemented what it actually used.

Why it matters:
It keeps code modular and prevents classes from carrying unnecessary baggage.

⚙️ D — Dependency Inversion Principle (DIP)

Definition:
Depend on abstractions, not on concrete implementations.

In plain English:
High-level modules (like your business logic) shouldn’t depend on low-level modules (like database classes). Both should depend on an interface or abstraction.

Example:
When I built a logging feature, I initially called a FileLogger class directly. Later, when we switched to DatabaseLogger, I had to change everything. The fix? Use a Logger interface, and just swap implementations.

Why it matters:
It makes your code flexible and easy to maintain when changing technologies or components.

🧠 Wrapping It All Up

The SOLID principles are like a set of guardrails — they don’t restrict your creativity; they just keep you from falling off the cliff.

Here’s a quick recap:

Principle	Stands For	Key Idea
S	Single Responsibility	One class = one job
O	Open/Closed	Extend without modifying
L	Liskov Substitution	Subclasses should behave like their parents
I	Interface Segregation	No unnecessary interface methods
D	Dependency Inversion	Depend on abstractions, not concretes

When I look back, I realize the biggest jump in my programming maturity came when I stopped focusing on just writing code and started focusing on designing it well.

So next time you’re building something — pause for a moment and ask,

“Am I being SOLID about this?”

📚 References

Higher Order Functions — Powering Modern JavaScript Magic

Devashish Roy — Sun, 19 Oct 2025 11:46:50 +0000

When I first started working with JavaScript, I used to think functions were just blocks of code — something you call, they do their job, and that’s it. But as my projects grew — from simple scripts to complex API-driven dashboards — I discovered something that completely changed how I write code: Higher-Order Functions (HOFs).

What Are Higher-Order Functions?

In simple terms, a higher-order function is a function that does one or both of these things:

Takes another function as an argument,
Returns a new function.

That’s it. But this simple idea gives us immense flexibility — allowing us to write cleaner, reusable, and more powerful code.

Real-Life Example — API Calls and Async Workflows

Imagine you’re building a dashboard that fetches data from multiple APIs — user profiles, posts, analytics, etc.

Normally, you’d call an API, handle its response, and move on. But what if you need to:

Retry failed API calls automatically
Log how long each request takes
Or show a loading spinner until all requests finish

Instead of writing repetitive code for each API call, you can use a higher-order function to handle this behavior.

Here’s an example 👇

// A higher-order function that wraps any async function with logging and retry logic
function withRetryAndLogging(asyncFunc, retries = 3) {
  return async function (...args) {
    for (let i = 0; i < retries; i++) {
      try {
        console.log(`Attempt ${i + 1}...`);
        const start = Date.now();
        const result = await asyncFunc(...args);
        console.log(`✅ Success in ${Date.now() - start}ms`);
        return result;
      } catch (error) {
        console.warn(`⚠️ Failed attempt ${i + 1}`);
        if (i === retries - 1) throw error;
      }
    }
  };
}

// Original function – just fetches data
async function fetchUserData(id) {
  const res = await fetch(`https://api.example.com/users/${id}`);
  return res.json();
}

// Wrapped function with extra behavior
const safeFetchUser = withRetryAndLogging(fetchUserData);

// Use it like a normal function
safeFetchUser(42);

Here, withRetryAndLogging is a higher-order function — it takes a function (fetchUserData) and returns a new one with extra capabilities.

This makes your code modular, reusable, and easier to maintain — a big win when working with asynchronous systems.

Other Real-World Examples

You’re already using HOFs — even if you don’t realize it:

setTimeout(() => {...}, 1000) — takes a callback function.
Array.map(), filter(), reduce() — take functions to process arrays.
Express.js middleware — functions that take another function (the next handler).

Each of these uses the same principle — passing functions as data to build flexible, composable systems.

Why It Matters

When working with asynchronous code like API calls, event listeners, or promises, higher-order functions give you:

Better abstraction – you can separate logic (like retry or logging) from the main task.
Code reuse – one wrapper can handle multiple API functions.
Cleaner structure – no repeated boilerplate or nested callbacks.

They’re the reason modern frameworks like React, Node.js, and Express feel so elegant — all powered by functions working with other functions.

Final Thought

Think of higher-order functions as the “middleware of logic.” Just as routers pass requests through layers of middleware before reaching the final handler, your code can pass data through layers of behavior — retry, logging, validation, or error handling — all made possible because functions in JavaScript are first-class citizens.

Once you start thinking in terms of higher-order functions, your code stops being just instructions — it becomes a system of composable, reusable logic.

References

Functions are First-Class Citizens — What Does It Mean?

Devashish Roy — Wed, 15 Oct 2025 18:00:22 +0000

Before understanding why functions are called first-class citizens in some programming languages and not in others, we need to understand what a first-class citizen means in a programming language.

What is a First-Class Citizen?

In programming, a first-class citizen (or first-class object) is an entity that can be treated like any other value in the language.

This means it can:

Be assigned to a variable.
Be passed as an argument to a function.
Be returned from a function.
Be stored in data structures (like lists, maps, etc.).

Example — Functions as First-Class Citizens (Python)

def greet():
    return "Hello"

# 1. Assigned to a variable
say_hello = greet

# 2. Passed as an argument
def call_func(func):
    print(func())

call_func(say_hello)

# 3. Returned from a function
def outer():
    return greet

inner = outer()
print(inner())

Here, functions are first-class citizens because they can be assigned, passed, and returned.

Who Are the First-Class Citizens in Popular Languages?

C

✅ Primitive types (int, float, char)
✅ Pointers (including function pointers)
⚠️ Functions are not fully first-class — you can use function pointers, but no closures or nested functions.

→ First-class citizens: Variables, pointers, primitive types

C++

✅ Objects (instances of classes)
✅ Primitive types
✅ Lambdas / function objects (std::function) since C++11
⚠️ Regular functions are not first-class by themselves

→ First-class citizens: Objects, primitive types, lambdas, std::function

Java

✅ Objects (instances of classes)
✅ Lambdas and method references since Java 8
⚠️ Regular methods are not first-class

→ First-class citizens: Objects, lambdas (Java 8+)

JavaScript

✅ Functions (assignable, passable, returnable)
✅ Objects, arrays, primitives
✅ Closures supported

→ First-class citizens: Functions, objects, primitives

TypeScript

✅ Superset of JavaScript, same rules
✅ Functions, objects, primitives, classes
✅ Type annotations make function-as-value more explicit

→ First-class citizens: Functions, objects, primitives, classes

Python

✅ Everything is an object
✅ Functions, classes, modules, numbers, strings — all first-class

→ First-class citizens: Everything (especially functions and classes)

Go (Golang)

✅ Functions (assignable, passable, returnable)
✅ Interfaces, structs, primitives
✅ Closures supported

→ First-class citizens: Functions, structs, interfaces, primitives

First-Class Entities Matrix with Examples

Language	Entity	Assigned	Passed	Returned	Stored	Created
C	Primitive (`int`,`char`)	✅	✅	✅	✅	✅
	Pointer	✅	✅	✅	✅	✅
	Struct	✅	✅	✅	✅	✅
	Function	⚠️	⚠️	⚠️	⚠️	❌
C++	Primitive	✅	✅	✅	✅	✅
	Object	✅	✅	✅	✅	✅
	Pointer / Reference	✅	✅	✅	✅	✅
	Lambda / std::function	✅	✅	✅	✅	✅
Java	Primitive	✅	✅	✅	✅	✅
	Object	✅	✅	✅	✅	✅
	Lambda / Functional Interface	✅	✅	✅	✅	✅
	Class	❌	✅	❌	✅	✅
JavaScript	Function	✅	✅	✅	✅	✅
	Object	✅	✅	✅	✅	✅
	Array	✅	✅	✅	✅	✅
	Class	✅	✅	✅	✅	✅
	Primitive	✅	✅	✅	✅	✅
Python	Function	✅	✅	✅	✅	✅
	Object	✅	✅	✅	✅	✅
	Class	✅	✅	✅	✅	✅
	Module	✅	✅	✅	✅	✅
	Primitive	✅	✅	✅	✅	✅
Go	Function	✅	✅	✅	✅	✅
	Struct	✅	✅	✅	✅	✅
	Interface	✅	✅	✅	✅	✅
	Primitive	✅	✅	✅	✅	✅

Summary Table

Language	First-Class Citizens
C	Variables, pointers, primitive types
C++	Objects, primitive types, lambdas (std::function)
Java	Objects, lambdas (Java 8+)
JavaScript	Functions, objects, primitives
TypeScript	Functions, objects, primitives, classes
Python	Everything (functions, classes, modules, etc.)
Go	Functions, structs, interfaces, primitives

Why Functions Are First-Class Citizens in Some Languages

Functions are first-class citizens in languages like Python, JavaScript, Go, and TypeScript because they satisfy all the properties of first-class entities:

They can be assigned to variables
They can be passed as arguments
They can be returned from other functions
They can be stored in data structures
They can be created dynamically

In languages like C or Java (pre-Java 8), functions are not fully first-class because they cannot satisfy all these properties — e.g., you cannot create functions dynamically or return raw functions as easily.

In short: A first-class function is a function that can be treated just like any other value.

Languages differ in their support, and that’s why understanding first-class citizens helps you write more flexible, functional, and expressive code.

Docker Command Sheet - My Go-To Dev Environment

Devashish Roy — Sun, 21 Sep 2025 13:51:22 +0000

A quick reference for commonly used Docker commands.

Designed for everyday development, it shows how to build, run, manage, and push Docker images. Fully generalized with placeholders for paths, image names, container names, and ports. Minimal, non-redundant, and easy to follow for beginners and intermediate users alike.

Basic Docker Commands

# Check installed Docker version
docker version

# Pull an image from Docker Hub
docker pull <image_name>

# Build an image from a Dockerfile (path = directory containing Dockerfile)
docker build -t <image_name> <path_to_dockerfile>

# Run a container interactively
docker run -it <image_name>

# Run a container with port mapping (host → container)
docker run -p <host_port>:<container_port> <image_name>

# Run a container with a custom name
docker run -it --name <container_name> <image_name>

# List running containers
docker container ls

# List all containers (including stopped ones)
docker container ls -a

# Stop a container
docker stop <container_id>

# Remove a container
docker container rm <container_id>

# List all images
docker image ls

# Remove an image
docker image rm <image_id>

Docker Volumes

# Create a named volume
docker volume create <volume_name>

# List all volumes
docker volume ls

# Run a container with a mounted host directory
docker run -it -v <host_path>:<container_path> <image_name>

# Run a container with a named volume
docker run -it -v <volume_name>:<container_path> <image_name> bash

Docker Networking

# List all networks
docker network ls

# Inspect the default bridge network
docker inspect bridge

# Create a new network
docker network create <network_name>

# Run a container inside a specific network
docker run -it --network <network_name> --name <container_name> <image_name>

# Connect an existing container to a network
docker network connect <network_name> <container_name>

# Execute a command inside a running container
docker exec -it <container_name> bash

# Run a container with port mapping
docker run -it -p <host_port>:<container_port> <image_name>

Working with Docker Hub

# Build an image and tag it for Docker Hub
docker build -t <dockerhub_username>/<repo_name> <path_to_dockerfile>

# Push image to Docker Hub
docker push <dockerhub_username>/<repo_name>

# Pull image from Docker Hub
docker pull <dockerhub_username>/<repo_name>

# Run container from Docker Hub image
docker run -it <dockerhub_username>/<repo_name>

This cheatsheet provides a minimal, non-redundant, and fully generalized set of Docker commands for everyday development.

References

Run Oracle19c Database in Mac M1/M2 using Docker

Devashish Roy — Sat, 20 Sep 2025 13:40:28 +0000

Running Oracle 19c on Mac (M1/M2) isn’t straightforward. Unlike Windows or Linux, Oracle doesn’t provide a native installer, which can be a huge blocker for students and developers.

During my MTech 2nd semester Database Security Lab, I had to use Oracle 19c for practicals—but on my Mac, there was no direct installer available. Initially, I wasted a lot of time trying different hacks and workarounds just to get it running.

The breakthrough came when I used Docker. By containerizing Oracle 19c, I could run it seamlessly on macOS without hitting compatibility issues.

Repository Link: https://github.com/roydevashish/path-to-software-engineer

Documentation Link: https://github.com/roydevashish/path-to-software-engineer/blob/main/oracle19c-in-mac-m1-m2-using-docker.md

If you’re on macOS and struggling to run Oracle databases, this setup can save you hours of frustration.

Curious to know — have you ever used Docker as a workaround to bypass OS compatibility issues?

Prerequisite

Steps to follow

1. Download the Oracle Database 19c for LINUX ARM (aarch64) file

Go to the page -> Database Software Downloads | Oracle India and download Oracle Database 19c for LINUX ARM (aarch64) file.

2. Clone Repository oracle/docker-images

git clone github.com/oracle/docker-images

3. Copy or Move the file

Copy or Move the download file LINUX.ARM64_1919000_db_home.zip to docker-images/OracleDatabase/SingleInstance/dockerfiles/19.3.0.

4. Build the Image

Use terminal and navigate to docker-images/OracleDatabase/SingleInstance/dockerfiles.

Build the docker image by running the shell script:

./buildContainerImage.sh -v 19.3.0 -e

where

v: for version
e: for enterprise edition

5. List to check the images

docker images

The list must have an image docker/database with tag 19.3.0-ee.

6. Run the Docker Container

Run a docker container using the image:

docker run -d --name oracle19 -e ORACLE_PWD=mypassword1 -p 1521:1521 oracle/database:19.3.0-ee

where

-name: Name of the container
ORACLE_PWD: Password of your oracle database
p: Port mapping

7. Check the status of the container

Check the status of the container:

docker ps

The status should be healthy that means the container is up and running.

8. Download the VS Code Extension

Download the Oracle SQL Developer Extension for VSCode.

Create a New Connection with the following properties

Name: SYS
(You can give anything, but I like to keep the connection name as the username, so that I know which user is using this connection.)

Role: SYSDBA
Username: SYS
Password: mypassword1

Hostname: localhost
Port: 1521
Type: Service Name
Service Name: ORCLCDB

Click on Test to check the connection
Click on Save to save the connection
Click on the connection name to connect, it will ask for the password
Open a worksheet and run the SQL commands

References

Git Command Cheetsheet Sheet

Devashish Roy — Sat, 20 Sep 2025 13:39:57 +0000

A concise reference for Git commands.

⚙️ Configure Git

🌍 Global (applies to all repositories)

# Set global name
git config --global user.name "Your Name"

# Set global email
git config --global user.email "your@email.com"

📂 Local (specific to a repository)

# Set local name (for this repo only)
git config --local user.name "Your Name"

# Set local email (for this repo only)
git config --local user.email "your@email.com"

🏗️ Initialize & Clone

🆕 Initialize a Git repository

git init

📥 Clone a repository

# Clone into a new directory
git clone [url]

# Clone into the current directory
git clone [url] .

# Clone into a specific directory
git clone [url] [path-to-clone]

📌 Stage & Snapshot

🔎 Check file status

git status

➕ Add files to the staging area

# Stage a specific file
git add [file]

# Stage all files
git add .

➖ Remove files from the staging area

# Unstage a specific file
git reset [file]

# Unstage all files
git reset .

📝 Check file changes

# Show unstaged changes
git diff

# Show staged changes
git diff --staged

💾 Commit changes

# Commit with a message
git commit -m "Commit message"

# Commit with title and description
git commit -m "Commit title" -m "Commit description"

🌿 Branching

📋 List branches

git branch

🌱 Create a new branch

git branch [branch-name]

🔀 Switch to another branch

git checkout [branch-name]

✏️ Rename the current branch

git branch -M [new-branch-name]

🕒 View commit history

git log

🔄 Share & Update

🌐 Remote repositories

# Add a remote
git remote add [alias] [url]

# List remotes
git remote -v

# Show details of a remote
git remote show [alias]

# Get the URL of a remote
git remote get-url [alias]

# Remove a remote
git remote remove [alias]

📤 Fetching & pushing

# Fetch and merge changes from remote
git pull

# Push and set upstream for the first time
git push -u [alias] [branch]

# Push to a specific remote and branch
git push [alias] [branch]

# Push to the default remote/branch
git push

🚫 Ignoring Files

Create a .gitignore file to exclude files/folders from being tracked:

logs/
*.notes
pattern*/

📖 References

China Cracks Small RSA Key with Quantum Computer – What It Means for Our Digital Future

Devashish Roy — Sat, 20 Sep 2025 13:37:53 +0000

Imagine waking up one morning to find out the math behind the encryption protecting your bank account is slowly beginning to break. That’s exactly the kind of shift a recent breakthrough in China is hinting at — and while we’re not in immediate danger, it’s a wake-up call the world can't ignore.

🔓 What Happened?

A team of researchers from Shanghai University used a quantum annealing computer by D-Wave Systems to crack a 22-bit RSA key — a small feat in terms of practical encryption but a huge leap in terms of quantum capabilities.

They avoided the traditional Shor’s algorithm and instead reframed the problem as a combinatorial optimization task, ideal for D-Wave’s quantum annealers.

🧠 Why Should You Care About Just 22 Bits?

While a 22-bit key is not used in practice, this successful demonstration shows significant progress in real-world quantum cryptanalysis. It scaled beyond past limits and demonstrated strategies that could extend to larger key sizes.

📅 Visual Timeline: Quantum Threats to RSA and the Global Response

text
CopyEdit
1977 ─────► RSA encryption is introduced.
1994 ─────► Shor’s algorithm (theoretical RSA breaker) is proposed.
2019 ─────► Google achieves "quantum supremacy" in a limited task.
2022 ─────► NIST announces 4 finalists for post-quantum cryptographic standards.
2023 ─────► IBM & others build 400–1000+ qubit gate-based quantum processors.
2024 ─────► China factors a 22-bit RSA key using D-Wave quantum annealer.
2024 ─────► NIST releases FIPS 203–205: Official PQC standards.
2025 ─────► HQC selected as additional PQC candidate by NIST.
20XX ─────► Full-scale quantum computers pose real threat to 2048-bit RSA.

⚠️ We're here 👆 — and we’re already past the planning phase.

🛡 What’s the Risk?

RSA, ECC, and other traditional algorithms protect nearly everything online. Quantum computers, once powerful enough, could break these systems in minutes.

Governments and standards organizations are already preparing. The U.S. National Institute of Standards and Technology (NIST) is leading the global shift to post-quantum cryptography (PQC), using lattice-based algorithms like CRYSTALS-Kyber.

🚀 What Should You Do?

Whether you’re a developer, architect, or IT leader, now is the time to:

✅ Audit where your systems use RSA, ECC, SHA, or other vulnerable algorithms

✅ Start testing quantum-safe libraries like Open Quantum Safe

✅ Use hybrid schemes (classical + PQC) during the transition

✅ Design for crypto-agility, so you can update encryption without rewriting everything

🧩 Final Thoughts

RSA isn’t dead — yet. But history tells us that proof-of-concept attacks scale fast. Just like DES was declared broken four years after the first partial cracks, this 22-bit demonstration could be a preview of what’s coming.

If your systems handle sensitive, long-lived data like health records, personal identities, or financial data — you can't afford to wait.

🔐 The future of encryption is quantum-safe.

Start your transition before the quantum threat becomes a quantum disaster.

Networking and Digital Communication Fundamentals

Devashish Roy — Sat, 20 Sep 2025 13:36:35 +0000

1. Introduction

The basic of networking and digital communication and essential elements required to understand how computer network operates in the context of security of information system for out net-centric organisation.

1.1 Topics to be covered

Types of network
How network works
Routers
Gateways
Bridges
OSI Model
Network Topologies
Protocols

Network: Two or more devices connected together in such way as to allow them to exchange information.

Protocol: Set of standards that defines all operations within a network, basically it is an agreed upon formate for transmitting data between two devices. It determines a number of things in the network:

type of error check
data compression method, if any
indicate finished sending a message, or received a message
how devices outside the network can interact with the network

Protocol defines everything from basic networking data structure to upper level application programs.

2. Network Types

A network is a logical grouping of computers that share information and resources.

Common Categorisation:

LAN (Local Area Network)
WAN (Wide Area Network)

2.1 LAN (Local Area Network)

A LAN is a single network of computers, which are physically located in the same area and rarely spans over more than one location. It usually comprise small number of computers and printers with up to five servers.

Example - Network in a small office or home office.

2.2 WAN (Wide Area Network)

A WAN is a network of LANs. WANs span more than one geographic area and are used to connect remote offices to each other. Basically, a WAN comprises two or more LANs joined together by routers. It can be found in medium - to - large-sized businesses with more then one office location.

Routers are hardware devices that direct traffic from one LAN to another.

Example - A software company might have its headquarters in Delhi, but also have remote office locations, say in Aurangabad and Faridabad. The LAN in the Delhi office would be connected to the LAN in the remote offices forming a WAN.

ℹ️

LANs and WANs comes in many different varient. The most popular network type is Ethernet. Ethernet network have speeds of 10 Mbps, 100 Mbps or 1 Gbps. The majority of networks today operates at 100 Mbps. An alternative to Ethernet network is token-ring networks. Token-ring networks operates at 4 or 16 Mbps and are usually found in legacy system/networks. Token-ring networks are rarely found in companies today because of their lack of speed.

2.3 Key Terms

LAN: It is a system of network computers and other hardware, such as printers, that are in relatively close proximity to one another.
Backbone: It is a high-speed network that connects several LANs in a location, to provide services. Such as in a university campus several LANs are connected to provide electronic mail (e-mail) and Internet access service beyond the LAN environment.
MAN: MANs are larger than LANs, but smaller than WANs. MANs are usually characterised by very high speed connections using fiber optical cables or other digital media.

IEEE 802-2001 standard definition:
A MAN (metropolitan area network) is optimized for a larger geographical area than is a LAN, ranging from several blocks of building to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it is usually used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking for local network. Metropolitan area networks can span up to 50 km, devices used ate modem and wire/cable.
WAN: It is a geographically dispersed communications network, with many owners, linking computers for the purpose of communication with each other, such as a national network for airline reservations or railway reservation.
Value-added Network (VAN): It is a communication channel leased from a telephone company to offer customers with modern access to network services through a local or toll-free number.
Wireless Network: It is most commonly used to refer to a telecommunication network whose interconnections between nodes is implemented without the use of wires. Wireless telecommunications networks are generally implemented with some type of remote information transmission system that uses electromagnetic waves, such as radio waves.

3. Network Architecture

Network architecture can be described in two ways: peer-to-peer and client/server.

3.1 peer-to-peer

A peer-to-peer network is a grouping of personal computers such that all share information among each other. It usually comprise less than 10 computers. This type of network is for the users that requires very little computer service and security.

Security Issues

In peer-to-peer network, file storage is scattered among the computers and security is extremely low.
Susceptible to hackers and other malicious users because there is no solid security policy enforced.

3.2 client/server

A client/server network is a network comprising several workstation and one or more servers. Client (user) log in the server and gain access to their files.

Advantage over peer-to-peer network

An administrator can control the privileges of each user.
Files are stored centrally, simplifying data backup.
Security policies are implemented that protects the users’ information.

4. Network Topologies

Topology refers to the shape of a network or the network’s layout. How different nodes in a network are connected to each other and how they communicate. Each topology is suited to specific tasks and has its own advantages and disadvantages. The choice of topology is dependent on:

type and number of equipments being used.
planned application and rate of data transfer.
required response time.
cost.

4.1 Physical Topology Vs. Logical Topology

Physical topology is the physical layout of devices on a network. The way that the workstations are connected to the network through the actucal cables that transmit data, that is , the physical structure fo the network, is called the physical topology. Every LAN has a topology, that is, the way that the devices on a network are arranged and how they communicate with each other.

The logical topology, in contrast, is the way that the signals act on the network media, or the way that the data pass through the network from one device to the next without regard to the physical interconnection to the device. Logical topology is also called signal topology.

A network’s logical topology is not necessarily the same as its physical topology.

Logical topologies are bound to the network protocols that direct how the data move across a network. The ethernet protocol is a common logical bus topology protocol.

4.2 Mesh Topology

In this topology, the devices are connected with many redundant interconnections between the network nodes. In a true mesh topology, every node has a connection to every other node in the network.

One of the problems with mesh topology is that its cabling expenses are high and it takes extra efforts to track down cable faults.

4.3 Star Topology

In this topology, all devices are connected to a central hub. Nodes communicate across the network by passing data through the hub.

Advantages of star topology are: it becomes easy to add new workstations (nodes), it allows centralised control over the network and it allows centralised monitoring of the hub/network.

Disadvantage: if the hub fails, it cripples all the workstations connected to that hub, bringing the network performance to zero, and hub are expensive network components. in terms of cost.

In the connection with the start topology, the following important terms are used:

Hub: A common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it it copied to the other ports so that all segments of the LAN can see all the packets.
1. Passive Hub: A passive hub serves simply as a conduit for the data, enabling it to go from one device (or segment) to another.
2. Intelligent Hub: Intelligent hubs includes additional features that enables an administrator to monitor the traffic passing through the hub and to configure each port in the hub. Also called manageable hubs.
3. Switching Hub: Switching hubs reads the destination address of each packet and the forwards the packet to the correct port.
Port: An interface of the computer to which a device can be connected.
Packet: A piece of message transmitted over a packet-switching network. One if the key features of a packet is that it contains the destination address in addition to the data.
Packet Switching: Protocol in which message are divided into packets before they are sent. Each packet is then transmitted individually and can even follow different routes to its destination. Once all the packets forming a message arrive at the destination, they are recompiled into the original message.
Switching Hub: A special type of hub that forwards packets to the appropriate port based on the packet’s address.
Segment: A segment, in a LAN or other types of networks, is a section of a network that is bounded by bridges, routers or switches. Hubs and switches are used to connect each segment to the rest of the LAN.

4.4 Bus Topology

In this topology, all devices are connected to a central cable, called the bus or backbone.

In connection with the bus topology, the following important terms are used:

Bus: A collection of wires through which data are transmitted from one part of a computer to another.
Backbone: Another term for bus, the main wire that connects nodes. The term is often used to describe the main network connection composing the Internet.

In networking, a bus is a central cable that connects all devices on a LAN. It is also called the backbone.

4.5 Ring Topology

In this topology, all devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it.

Advantages:

Cable failures affect limited users.
Equal access is provided for all users.
Each workstation has full access speed to the ring.
Even when workstation numbers increase, performance diminishes only slightly.

Disadvantages:

Wiring cost.
Difficult connections.
expensive adaptors cards need to be used.

4.6 Tree Topology

This is a hybrid topology. Groups of star-configured networks are connected to a linear bus backbone.

5. The OSI Seven Layer Model

The OSI is an International Organisation for Standardisation (ISO) standard for worldwide communications that defines a networking framework for implementing protocols in seven layers.

The OSI reference model is a set of seven layers that defines the different stages that data must go through to travel from one device to another over a network. It is also referred as the OSI reference model or just the OSI model.

5.1 Application Set

5.1.1 Layer 7 - Application

This is the layer that actually interacts with the operating system (OS) or application whenever the user transfers files, reads messages or perform other network related activities. The application layer supports application and end-user processes. Everything at this layer is application specific. This layer provides application services for file transfers, e-mail and other network software services.

5.1.2 Layer 6 - Presentation

It takes the data provided by the application layer and converts it into a standard formate that the other layers can understand. The presentation layer provides independence from differences in data presentation by translating from application to network formate and vice versa.

The presentation layer works to transform data into the form that the application layer can accept. This layer formates and encrypt data to be sent across a network, providing freedom from compatibility problems.

The presentation layer is sometimes called the syntax layer.

5.1.3 Layer 5 - Session

This layer establishes, maintains and ends communication with the receiving device. It establishes, manages and terminates conversations, exchanges and dialogues between the applications at each end. It deals with session and connection coordination.

5.2 Transport Set

5.2.1 Layer 4 - Transport

This layer maintains flow control of data and provides for error checking and recovery of data between the devices.

Transport layer looks to see if data are coming from more then one application and integrates each application’s data into a single stream for the physical network. This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery. It ensures complete data transfer.

5.2.2 Layer 3 - Network

The format, in which the transmitted data will be sent to the recipient device, is determined in this layer. Logical protocols, routing and addressing are handled here.

Network layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, inter-networking, error handling, congestion control and packet sequencing.

5.2.3 Layer 2 - Data

In this layer, the appropriate physical protocol is assigned to the data. Also, the type of network and packet sequencing are defined. At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronisation.

In Institute of Electrical and Electronics Engineer (IEEE) 802 networks, the data link control (DLC) layer is divided into two sublayers:

The media access control (MAC) layer
logical link control (LLC) layer

MAC is a hardware address that uniquely identifies each node of a network. The MAC layer interface directly with the network medium. Consequently, each different type of a network medium requires a different MAC layer. The MAC sublayer controls how a computer on the network gains access to the data and permission to transmit it.

The LLC layer controls frame synchronisation, flow control and error checking.

5.2.4 Layer 1 - Physical

This is the level of the actual hardware. It defines the physical characteristics of the network such as connections, voltage levels and timing. This layer conveys the bit stream electric impluse, light and radio signal through the network at the electric and mechanical levels. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects.

6. Network Components

The network components can be both software and hardware elements. Some of the key hardware components of computer networks are:

Cables
1. Coaxial Cable
  1. Thin Ethernet
  2. Thick Ethernet
  3. Twisted Pair
network adapter cards
hubs and switching hubs
routers
gateways and bridges
firewalls.

6.1 Network Cables

There are two most popular types of network cabling:

twisted pair (also known as 10BaseT)
thin coax (also known as 10Base2)

10BaseT was used with 10Mbps. 10BaseT cabling looks like an ordinary telephone wire, except that is has eight wires inside instead of four.

Thin coax looks like the copper coaxial cabling that is often used to connect a videocassette recorder to a television set.

10baseT or Cat5 cables are used for most home and small business networks. They are thin, easy to manipulate are easy to purchase as they come in custome lengths. The 10baseT/Cat5 cables have connectors that resemble a phone cord connector, only larger. These are called RJ-45 connectors.

6.2 Network Adapter Cards

Network adapter cards (NIC: Network Interface Card) plays an important role in computer networks on which modern IS reside. A network computer is connected to the network cabling with an NIC.

6.3 Hub and Switching Hub or the Switch

A hub is the central connecting device in a network. It is a box that is used to gather groups of PCs together at a central location with 10BaseT cabling.

For small networks (such as peer-to-peer network), it is possible to get by with a hub, some 10BaseT cables and a handful of network adapters.

Larger network often use a thin coax ‘backbone’ that connects a row of 10BaseT hubs together. Each hub, in turn, may connect a handful of computers together using 10BaseT cabling, which allows you to build networks of tens, hundreds or thousands of computers.

The switching hub, sometimes called a ‘switch’, is a more advanced unit over the basic hub. In a basic hub, all the computers connect to it and the speed of the Internet is defined by the slowest computer network card connected.

Switching hub treats each network card independently. The switching hub allows all the faster connections to remain at a higher speed and still interacts with the slow system.

6.4 Routers

Network is a heterogeneous environments. In such environments, there is a need of connection device that would interconnect two different technologies.

The router serves as a routing switchboard. It is a special computer that is dedicated to the task of interconnecting networks. It moves the information from its source to its destination regardless of the middleware.

Routers connect two or more networks and forward data packets between them. When data arrive from one of the segments, the router decides, according to its routing table, to which segment to forward the data.

6.5 Gateways and Bridges

A gateway is a legacy term, that is, it is a term that was used in the earlier days of computer networking. It once used to refer to a routing device. Today, in the TCP/IP world, the term gateway now refers to special-purpose devices that performs protocol conversions. Gateways implement application layer conversions of information received from various protocols.

A bridge is an electric device that connects and passes packets between two network segments. In general, a bridge will forward or discard an incoming frame based on the MAC address of that frame.

6.6 Firewalls

A firewall is a system designed to prevent unauthorised access to or from a private network. Firewall can be implemented in both hardware or software, or a combination of both. They are frequently used to prevent unauthorised Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.

Types of firewall techniques:

Packet filter: This involves looking at each packet entering or leaving the network and accepts or rejects it on the basis of user defined rules.
Application gateway: This applies security mechanisms to specific applications, such as file transfer protocol (FTP) and Telnet severs.
Circuit-level gateway: In this, security mechanism are applied when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.
Proxy server: This is used to intercept all messages entering and leaving the network. The proxy server effectively hides the true network addresses.

7. Network Protocols

A network protocol is basically an agreed-upon format for transmitting data between two devices. It is a standard set of rules that determines how systems will communicate across network. Two different systems can communicate and understand each other only if they use the same protocol in spite of their differences.

7.1 TCP/IP

TCP is one of the main protocols in TCP/IP networks. Whereas the IP deals only with the packets, TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent. IP specifies the format of packets, also called datagrams, and the addressing scheme. Most networks combines IP with a higher level protocol called TCP, which establishes a virtual connection between a destination and source.

7.2 Link Protocol

Link protocol plays a role at layer 2 of the OSI model (the data link layer). In communication, there is transmission of a unit of data from one node to another. It is responsible for ensuring that the bits received are the same as the bits sent. There are two categories of data transmission:

synchronous
asynchronous

Asynchronous means not synchronised, that is, not occourring at perdetermined or regular intervals. The term ‘asynchronous’ is usually used to describe communication in which data can be transmitted intermittently rather than in a steady steam.

The difficulty with asynchronous communication is that the receiver must have a way to distinguish between valid data and noise. In computer communications, this is usually accomplished through a special start bit and a stop bit at the beginning and end of each piece of data. For this reason, asynchronous communication is sometimes called start-stop communication.

Synchronous communication occurs at regular intervals.

7.3 OSI Protocol

OSI is an information exchange standard developed by the ISO in the early 1980s. The structure of the OSI in terms of its underlying protocols is as follows:

physical layer
datalink layer
network layer
transport layer
session layer
presentation layer
application layer

7.4 Routing Protocol

Routing protocols allow different computer networks to communicate. Some commonly used routing protocols are:

router information protocol (RIP)
open shortest path first (OSPF)
interior gateway routing protocol (IGRP)
enhanced IGRP (EIGRP)
border gateway protocol (BGP)
intermediate system to intermediate system (IS - IS)
constrained shortest path first (CSPF)

IGRP and EIGRP are proprietary Cisco protocols, and are supported on Cisco routers or other vendors’ routers to which Cisco has licensed the technology.

7.5 Tunneling Protocol

Tunneling is to do with VPN (Virtual Private Network). A tunneling protocol is a network protocol that encapsulates open protocol or session inside another. Protocol A is encapsulated within protocol B, such that A treats B as though it were a data link layer. Tunneling may be used to transport a network protocol through a network that would not otherwise support.

Examples of Tunneling Protocols:

Datagram - based
1. layer 2 tunneling protocol (L2TP)
2. multi-protocol label switching (MPLS)
3. generic routing encapsulation (GRE)
4. general packet radio service (GPRS) tunneling protocol (GTP)
5. point-to-point tunneling protocol (PPTP)
6. point-to-point protocol over Ethernet (PPPoE)
Stream-based
1. transport layer security (TLS)
2. secure shell (SSH)

8. Working of Network and the Internet

No one really ‘owns’ the Internet! It is a global collection of networks, both big and small. Under the Internet scheme, networks all over the world connect together in many different ways to form the single entity that is known as the ‘Internet’.

Typically, people connect to the Internet in two ways: while at work and while using the LAN connection through the ISP contract. The ISP may then connect to a larger network and become part of it. While at home or a remote location, most people typically connect to the Internet using the combination of modem and dial-up service. Either ways, when anyone connects to the Internet, his/her computer becomes a part of a network whose span is global.

POP (Point of Presence)
Most large corporations have their own dedicated backbones connecting various regions. In each region, the company has a point of presence (POP). The POP is a place for local users to access the company’s network, often through a local phone number or dedicated line.

9. Telecommunication Links and Other Important Related Topics

9.1 Circuit Switching and Packet Switching

Circuit Switching is a type of communication in which a dedicated channel (or circuit) is established for the duration of a transmission. The most ubiquitous circuit-switching network is the telephone system, which links together wire segments to create a single unbroken line for each telephone call. This system is ideal for communications that requires data to be transmitted in real time. These networks are sometimes called connection oriented networks.

Packet switching is a method in which messages are divided into packets and sends each packet individually. The Internet is based on a packet-switching protocol - the TCP/IP. Packet switching networks are more efficient if some amount of delay is acceptable. These networks are connectionless networks, a packet switching network can be made connection oriented by using a higher level protocol. Example: TCP, makes IP networks connection oriented.

9.2 Host

A host is a computer system that is accessed by a user working at a remote location. Typically, the term is used when there are two computer systems connected by modems and telephone lines.

9.3 Dedicated Server

Dedicated means being reserved for a specific use. A dedicated server is a single computer in a network reserved for serving the needs of the network.

9.4 Workstation

A ‘workstation’ is a type of computer used for engineering applications, desktop publishing, software development and other type of applications that require a moderate amount of computing power and relatively high-quality graphic capabilities. In the context of networking, workstation refers to any computer connected to a LAN. It could be workstation or a PC.

9.5 Channel and Node

A channel is a transmission path. A transmission channel is the path between two nodes of a network that a data communication follows. The term can refer to the physical cabling that connects the nodes on a network, the signal that is communicated over the pathway or a subchannel in a carrier frequency.

A node is a processing location in a network. A node can be a computer or some other device, such as printer. Every node has a unique network address, called as MAC address.

9.6 Contention

In the context of computer networks, contention means competition for resources. The term is used especially in network to describe the situation where two or more nodes attempt to transmit a message across the same wire at the same time. A contention is also a type of network protocol that allows nodes to contend for network access. That is, two or more nodes may try to send message across the network simunltaneously. The contention protocol defines what happens when this occurs.

9.7 CSMS/CD

CSMA/CD is a set of rules determining how network devices respond when two devices attempts to use a data channel simultaneously (called a ‘collision’).

9.8 Twisted-Pair Cable

This is a type of cable that consists of two independently insulated wires twisted around one another.

9.9 Coaxial Cable

A coaxial cable is a type of wire that consists of a centre wire surrounded by insulation and the a grounded shield of braided wire.

9.10 Fiber Optics

Fibre optics is a technology that uses glass (or plastic) threads (fibers) to transmit data. A fiber optic cable consists of a bundle of glass threads, each or which is capable of transmitting messages modulated onto light waves.

9.11 Token, Token Passing and Token-Ring Network

In the networking context, a token is a special series of bits that travels around a token ring network. As the token circulates, computers attached to the network can capture it. The token acts like a ticket, enabling its owner to send a message across the network. There is only one token for each network, so there is no possibility that two computers will attempt to transmit message at the same time.

Token passing uses a token, or series of bits, to grant a device permission to transmit over the network. Whichever device has the token, can put data into the network. When its transmission is complete, the device passes the token along to the next device in the topology.

A token ring network is a type of computer network in which all the computers are arranged in a circle. A token, which is a special bit pattern, travels around the circle. To send a message, a computer catches the token, attaches a message to it and then lets it continue to travel around the network.

9.12 IEEE 802.5 Token Ring

A short message (called a token) is circulated around the ring, passed from station to station. A station that wants to transmit waits for the token to arrive.

When the token arrives, the station change it from a token to a connector message and appends its message. This new message is then placed on the outgoing side of the ring. Each station passes on received tokens if they have nothing to transmit.

The workstations monitor connector messages to see if the message is addressed to them. If connector message are addressed to them, they copy the message, modify it to signify its receipt and then send it on around the ring. Connector messages that are not addressed to them are passed directly on to the next station in the ring. When the connector message travels full circle and arrives at the original sending station, it checks the message to see if it has been received. It then discards the message and replace it with a token.

9.13 CAM and Polling Mechanisms

CAM is short for channel access method, a protocol for how data are transmitted in the bottom two layers of the OSI mode (the physical and the data link layer). Polling, contention and token passing are three examples of CAMs.

Polling is CAM. In a master-slave scenario, the master queries each slave device in turns as to whether it has any data to transmit. If the slave answers yes, then the device is permitted to transmit its data. If the slave answers no, then the master moves on and polls the next slave device. This process is repeated continuously.

Django deployment on AWS

Devashish Roy — Sat, 20 Sep 2025 13:31:25 +0000

Today we are going to deploy our Django project in AWS. Our Django project’s code are stored in the GitHub repository, and we have an EC2 instance created and running with ubuntu 18.04 LTS operating system in AWS. We are going to see the steps to deploy our Django project from GitHub to AWS EC2 instance.

Prerequisite

Before going to the steps and setting up our server, we have a checklist, go through it and make sure it’s done before going through the steps.

Checklist

Django Project

You must have a Django project which is completed or it runs without any error, and the Django project must stored inside the django_deployment directory.
GitHub repository

After having the Django project you must push all the codes into the GitHub repository.
AWS (Amazon Web Services)

You will need a free or paid AWS account with an EC2 instance created and running with ubuntu 18.04 LTS and also it should accept all the public request from http and https method.

Setup our EC2 instance

⚠️ Note: For my convenience I am renaming EC2 instance to cloud computer. From now on whenever their is cloud computer it means EC2 instance.

Till now we have created our cloud computer and it’s running ubuntu 18.04 LST operating system. Now our task is to download and configure the software package to run our Django project. To run our Django application we need:

python3-dev
python3-venv
python-pip
SQLite
git

So let’s install all the required software dependencies for our project. Before doing so we are going to update our system for the latest software packages.

Run these two commands to update and upgrade all the software packages installed in the system.

apt-get update
apt-get upgrade

By using these two commands we have completed our system update.

Now we are going to install all the software packages we need for our Django project.

apt-get install -y python3-dev python3-venv sqlite python-pip git

By using the above command we have installed the required software packages.

At this point we have done our cloud computer setup.

Next we are going to setup our Django project in the cloud computer.

Django project setup

We are going to save all of our work in the /usr/local/workspace directory. So from now on whenever I use WORKSPACE directory it means /usr/local/workspace directory.

First we are going to create an apps directory inside our WORKSPACE directory. In this directory we are going to store our all projects.

mkdir -p /usr/local/workspace/apps

Now we are going to clone our Django project from GitHub.

git clone https://github.com/<username>/github_repo.git /usr/local/workspace/apps/django_deployment

Using the above git command we have cloned our Django project from GitHub to our cloud computer and it is stored inside the WORKSPACE/apps/django_deployment directory.

Now we going to create and env directory inside our WORKSPACE directory. Inside this directory we are going to store virtual environments for our projects.

mkdir -p /usr/local/workspace/env

Now let’s create a virtual environment for our Django project.

python3 -m venv /usr/local/workspace/env/django_deployment

After creating the virtual environment we need to install the requirements of our Django project, all the requirements of our Django project are stored in the requirements.txt file inside the project directory.

/usr/local/workspace/env/django_deployment/bin/pip install -r /usr/local/workspace/apps/django_deployment/requirements.txt

The above command will install all the requirements of our Django project inside the virtual environment.

Now we are going to run migrations and create static files for our Django project.

/usr/local/workspace/env/django_deployment/bin/python /usr/local/workspace/apps/django_deployment/manage.py makemigrations
/usr/local/workspace/env/django_deployment/bin/python /usr/local/workspace/apps/django_deployment/manage.py migrate
/usr/local/workspace/env/django_deployment/bin/python /usr/local/workspace/apps/django_deployment/manage.py collectstatic --noinput

At this point we are done with the Django project setup.

Next is to install and configure our supervisor and nginx server so that we can accept and process requests and give them responses.

Server setup

We need supervisor and nginx, two software packages, supervisor to run our Django project’s python files and nginx to serve Django project’s static files.

Let’s first install both the software packages.

apt-get install -y supervisor nginx

Configure supervisor

supervisor uses configuration files to manage processes. All the configuration files of supervisor is stored inside /etc/supervisor/conf.d

Create a configuration file for supervisor.

nano /etc/supervisor/conf.d/django_deployment.conf

This command will open a code editor inside the terminal. We need to write our configuration inside this. The configuration file includes this

[program:django_deployment]
environment =
    DEBUG=0
command = /usr/local/workspace/env/django_deployment/bin/uwsgi --http-socket :9000 --wsgi-file /usr/local/workspace/apps/django_deployment/django_server/wsgi.py
directory = /usr/local/workspace/apps/django_deployment
user = root
autostart = true
autorestart = true
stdout_logfile = /var/log/supervisor/django_deployment.log
stderr_logfile = /var/log/supervisor/django_deployment_err.log

Press CTRL + X, it will prompt yes or no to save it, press y and then enter to confirm and after that it will ask for the file name which we have already provided at the time of nano command as django_deployment.conf, so press enter. It will save and exit the code editor.

This will create a program / process named django_deployment and it will run our Django project using wsgi.py file.

Now need to update our process list and restart the processes.

supervisorctl reread
supervisorctl update
supervisorctl restart django_deployment

This three commands will update the process list and restart our django_deployment process. To check the status of the processes you can use status option with supervisorctl command, this will list all the processes with their current status.

supervisorctl status

Now we are done with the supervisor configuration.

Next we are going to configure nginx so that we can serve the static files of our Django project.

Configure nginx

nginx also uses configuration files to manage the server configurations. All the configuration files of nginx is stored inside /etc/nginx directory and the sites available to serve, their configurations are stored inside the /etc/nginx/sites-available directory.

For our Django project we are going to create a configuration file for nginx to serve the static files.

nano /etc/nginx/sites-available/django_deployment.conf

This command will open a code editor inside the terminal. We need to write our configuration inside this. The configuration file includes this

server {
    listen 80 default_server;

    location /static {
        alias /usr/local/workspace/apps/django_deployment/static;
    }

    location / {
        proxy_pass        http://127.0.0.1:9000/;
        proxy_set_header  Host                $host;
        proxy_set_header  X-Real-IP           $remote_addr;
        proxy_set_header  X-Forwarded-For     $remote_addr;
        proxy_set_header  X-Forwarded-Proto   $scheme;
        proxy_redirect    off;
    }
}

This will create the configuration file for nginx to server our static files which will create and stored inside the /usr/local/workspace/apps/django_deployment/static directory

Now we need to remove a file /etc/nginx/sites-enabled/default and in place of this file we need to create a link from a file to the configuration file /etc/nginx/sites-available/django_deployment.conf

rm /etc/nginx/sites-enabled/default
ln -s /etc/nginx/sites-available/django_deployment.conf /etc/nginx/sites-enabled/django_deployment.conf

Now we need to restart the server so that the updated configuration comes in action.

systemctl restart nginx.service

Now we are done with the nginx configuration.

So, till at this point we can see our Django project running and live on internet, and we can check it in the web browser.

Update changes

Update local computer and push to GitHub

First we are going to change and update our files inside the local machine, and then we will commit these changes and push it to the GitHub.

Pull the updated file from GitHub to cloud computer

Now we will pull the updated files from GitHub.

To pull the file change directory to the project directory

cd /usr/local/workspace/apps/django_deployment

Now run the pull request

git pull

Now git will pull all the updated files for you and update your code.

Effect the changes

Now we are going to run migrations and create static files for our Django project.

Note: Go through these steps if you have done changes in the database and static files. And if you are in doubt just go through these, if their will be any changes they will take care of it.

/usr/local/workspace/env/django_deployment/bin/python /usr/local/workspace/apps/django_deployment/manage.py makemigrations
/usr/local/workspace/env/django_deployment/bin/python /usr/local/workspace/apps/django_deployment/manage.py migrate
/usr/local/workspace/env/django_deployment/bin/python /usr/local/workspace/apps/django_deployment/manage.py collectstatic --noinput

Restart the supervisor process

Now restart the supervisor process to effect the changes.

supervisorctl restart django_deployment

Time to check our live site

Now it’s time to hit the web browser with the URL. After going to the URL you can see your live Django project direct from your cloud computer.