Forem: Lucas Vieira

Free, Open-Source LocalStack Alternative for AWS Testing

Lucas Vieira — Sat, 11 Apr 2026 14:36:32 +0000

In March 2026, LocalStack replaced its Community Edition with a proprietary image that requires an account and auth token. For teams that relied on LocalStack for local AWS testing, this broke CI pipelines and forced a choice: pay for a Pro license or find an alternative.

fakecloud is that alternative.

What is fakecloud?

fakecloud is a free, open-source local AWS emulator for integration testing and local development. It runs on a single port (4566), requires no account or auth token, and aims to faithfully replicate AWS behavior.

Currently supports 20 AWS services with 1,000+ API operations:

S3 — objects, multipart uploads, versioning, lifecycle, notifications
Lambda — real code execution via Docker, 13 runtimes, event source mappings
SQS — FIFO queues, dead-letter queues, long polling
SNS — fan-out to SQS/Lambda/HTTP, filter policies
DynamoDB — tables, transactions, PartiQL, streams, global tables
EventBridge — pattern matching, scheduled rules, API destinations
RDS — PostgreSQL/MySQL/MariaDB via Docker, snapshots, read replicas
ElastiCache — Redis/Valkey via Docker, replication groups, failover
SES — v2 API (97 operations), inbound email pipeline, event destinations
Cognito User Pools — authentication, MFA, user management
Kinesis — data streams, shard iterators, stream retention
Step Functions — ASL interpreter, Lambda/SQS/SNS/DynamoDB integrations
CloudWatch Logs — groups, streams, filtering, subscriptions
API Gateway v2 — HTTP APIs with Lambda integration
IAM, STS, SSM, Secrets Manager, KMS, CloudFormation

Full service list with operation counts

LocalStack vs fakecloud

In March 2026, LocalStack moved many previously-free services behind a paywall (Cognito, SES v2, RDS, ElastiCache, ECR, ECS). The Community Edition now requires authentication and has limited service availability.

Feature	fakecloud	LocalStack Community
License	AGPL-3.0 (free, open-source)	Proprietary
Auth required	No	Yes (account + token)
Commercial use	Free	Paid plans only
Docker required	No (standalone binary)	Yes
Startup time	~500ms	~3s
Idle memory	~10 MiB	~150 MiB
Install size	~19 MB binary	~1 GB Docker image
AWS services	20	30+
Test assertion SDKs	TypeScript, Python, Go, Rust	Python, Java
Cognito User Pools	80 operations	Paid only
SES v2	97 operations	Paid only
SES inbound email	Real receipt rule action execution	Stored but never executed
RDS	22 operations, PostgreSQL/MySQL/MariaDB via Docker	Paid only
ElastiCache	44 operations, Redis/Valkey via Docker	Paid only

LocalStack has more services overall, but many are behind a paywall. fakecloud focuses on implementing fewer services completely, with 100% conformance to AWS behavior.

Why we built fakecloud

LocalStack went proprietary. In March 2026, localstack:latest started requiring authentication. CI pipelines broke. The message was clear: LocalStack Community Edition was no longer community.

Correctness matters for testing. If you're building on AWS, your integration tests should talk to something that behaves like AWS — not mocks that return fake success responses. When fakecloud behaves differently from AWS, that's a bug we fix.

Real infrastructure, not stubs. fakecloud runs actual software via Docker: real Lambda runtimes (13 languages), real databases (PostgreSQL, MySQL, MariaDB), real Redis/Valkey instances. When your Lambda function reads from RDS, it's talking to an actual Postgres instance, not a mock.

Testing tools should be free. fakecloud is a development dependency, not production infrastructure. It should be free and open-source, the same way test frameworks like Jest, Mocha, and pytest are free.

How we verify correctness

fakecloud doesn't claim to be "AWS-compatible" without backing it up:

34,000+ conformance test variants validated against official AWS Smithy models, covering every operation parameter, boundary condition, and error case
280+ end-to-end tests using the official AWS SDKs (aws-sdk-rust, boto3, aws-sdk-js)
Automated testing against real AWS — our test suite runs against both fakecloud and actual AWS to verify behavioral parity

When tests fail, we fix the behavior. We don't stub responses or return fake success codes.

Getting started

Install and run fakecloud:

curl -fsSL https://raw.githubusercontent.com/faiscadev/fakecloud/main/install.sh | bash
fakecloud

Or via Docker:

docker run --rm -p 4566:4566 ghcr.io/faiscadev/fakecloud

Point your AWS SDK at http://localhost:4566 with dummy credentials:

aws --endpoint-url http://localhost:4566 sqs create-queue --queue-name test-queue

Test assertions with fakecloud SDKs

fakecloud exposes introspection endpoints that AWS doesn't provide, so you can assert on side effects in your tests:

import { FakeCloud } from "fakecloud";

const fc = new FakeCloud("http://localhost:4566");

// After your app sends an email via SES
const { emails } = await fc.ses.getEmails();
expect(emails).toHaveLength(1);
expect(emails[0].destination.toAddresses).toContain("user@example.com");

// After your Lambda processes an event
const { invocations } = await fc.lambda.getInvocations();
expect(invocations[0].statusCode).toBe(200);

SDKs available for TypeScript, Python, Go, and Rust.

What's not implemented (yet)

fakecloud is younger than LocalStack and has fewer services. If you need EC2, ECS, or other services not listed above, LocalStack may still be your best option (if you're willing to pay for Pro).

We're prioritizing services based on real-world demand. Open an issue if there's a service you need.

Roadmap

Coming next:

Bedrock — AI/ML testing (high demand across the ecosystem)
Lambda Containers — practical container support with ECR
CloudFront — CDN configuration testing
CloudWatch Metrics — complete monitoring story alongside Logs
Athena — SQL analytics on S3
More RDS engines (Oracle, SQL Server)

Full roadmap

Other alternatives to LocalStack

Moto — Python-based AWS mocking library. More services than fakecloud (100+), but designed for unit tests with mocks rather than integration tests. Doesn't support cross-service integrations or real Lambda execution.

LocalStack Pro (paid) — If you need the full service catalog and don't mind paying, LocalStack Pro is mature and feature-complete.

Real AWS — For the highest fidelity, test against real AWS. fakecloud is for fast local iteration; real AWS is for pre-production validation.

Try fakecloud

Repo: github.com/faiscadev/fakecloud
Site: fakecloud.dev
Install: curl -fsSL https://raw.githubusercontent.com/faiscadev/fakecloud/main/install.sh | bash

If you find a case where fakecloud behaves differently from AWS, open an issue — that's a bug, and we'll fix it.

Originally published at fakecloud.dev

Why I'm building a free, open-source AWS emulator

Lucas Vieira — Mon, 06 Apr 2026 22:27:35 +0000

A few days ago, our CI started failing. The culprit: localstack:latest now requires an account and an auth token. Broken builds.

I'd seen LocalStack creeping toward proprietary for a while, but this was the moment it actually hit. A colleague noticed it at the same time as me, but I was already working on a fix. I patched the build, but the question stuck: how long can we keep using the old version until we start having real problems?

I don't trust mocks

I should back up. I care about tests a lot. Enough to become a maintainer of Chai.js. Enough that when I build something, the test infrastructure comes first.

But I have a specific opinion about what kind of tests matter. I hate mocks. Not the concept — the way most codebases use them. You end up with tests that don't test anything real. You're asserting that you call functions in the right order. You're verifying the plumbing, not the behavior.

The worst part is when mocked tests give you false confidence. I've seen tests that assert you do the wrong thing successfully — the mock doesn't care, it just returns what you told it to. Your tests pass. Your code has a bug. You ship it.

If you're building on AWS, you need integration tests that actually talk to something that behaves like AWS. Not a mock. Not a stub that returns 200 to everything. Something that implements the real behavior: if you call API A then API B, and AWS would produce side effect C, then your test environment should produce side effect C too.

That's what LocalStack used to give us. And that's what I wanted to keep — but free and open source.

So I built it

I started fakecloud on April 4th, 2026. Three days later: 13 AWS services, 300+ commits, 1,000+ tests.

That pace was possible because of two things. First, I used LLMs heavily throughout — not to generate code I don't understand, but as a force multiplier with strong guardrails. Every feature ships with E2E tests. The tests are the guardrails. If the LLM generates something that doesn't match real AWS behavior, the tests catch it.

Second, Rust. I chose Rust because I love static-typed compiled languages, and Rust's type system is genuinely amazing. You get the performance of no garbage collector without having to manually manage memory. It means fakecloud starts in under 100ms and runs as a single binary — no Docker required, no runtime dependencies.

Correctness is the whole point

fakecloud doesn't try to be a scalable production cloud. It's not that. It's a testing tool. And the one thing a testing tool needs to get right is correctness.

What does that mean in practice? If you call CreateQueue, then SendMessage, then ReceiveMessage on real AWS and get back your message with specific attributes — fakecloud should do exactly the same thing. If it doesn't, that's a fakecloud bug.

We currently verify this with 280+ E2E tests that use the official aws-sdk-rust crate and 34,856 auto-generated conformance test variants validated against official AWS Smithy models — covering all 983 API operations across 13 services at 100% conformance. The plan for the near future: set up a real AWS account and run our test suite against both fakecloud and real AWS side by side, so we can verify behavioral parity automatically.

What's here today

13 services, 983 API operations, all open source, all free:

S3 (107 actions) — objects, multipart uploads, versioning, lifecycle, notifications, encryption
SQS (23 actions) — FIFO queues, dead-letter queues, long polling, batch operations
SNS (34 actions) — fan-out to SQS, HTTP delivery, filter policies, platform applications
EventBridge (57 actions) — pattern matching, scheduled rules, connections, API destinations, endpoints
IAM (128 actions) — users, roles, policies, groups, instance profiles, OIDC/SAML providers
STS (11 actions) — assume role, session tokens, federation, credential expiration
SSM (146 actions) — parameters, documents, commands, maintenance windows, associations, automation, sessions
DynamoDB (57 actions) — tables, items, transactions, PartiQL, backups, global tables, streaming
Lambda (10 actions) — function CRUD, invoke, event source mappings
Secrets Manager (23 actions) — versioning, soft delete, rotation, replication, resource policies
CloudWatch Logs (113 actions) — groups, streams, filtering, deliveries, transformers, anomaly detection
KMS (53 actions) — encryption, aliases, key management, grants, custom key stores
CloudFormation (8 actions) — template parsing, resource provisioning

Services talk to each other: S3 notifications deliver to SNS/SQS. SNS fans out to SQS. EventBridge rules fire on schedule and deliver to targets. This is the kind of cross-service behavior that matters in integration tests and that most emulators get wrong or skip entirely.

Try it

curl -fsSL https://raw.githubusercontent.com/faiscadev/fakecloud/main/install.sh | bash
fakecloud

Then point any AWS SDK at http://localhost:4566 with dummy credentials. That's it.

The code is at github.com/faiscadev/fakecloud. It's AGPL-3.0 — free and open source, including for commercial use.

If you need a local AWS emulator for your integration tests, give it a try. And if something doesn't behave like real AWS — open an issue. That's a bug, and we'll fix it.