My first open source contribution

Eddie Hale — Thu, 17 Oct 2019 13:03:41 +0000

Cover image credit to @yancymin on unsplash

For a while I've traversed GitHub and come up with excuses as to why I couldn't step in and help with a particular project. Some of the more frequent ones were:

I don't know that language well enough to be of any benefit.
They already have so many smarter people working on this, how can I bring value?

These projects are more than just code - there's documentation, refactoring, testing...everything you would find in a normal project. Yesterday I finally stepped out of that comfort zone and took the plunge to make my first contribution - to dev.to!

No, I don't know the project very well (it has some great docs). No, I technically didn't write any code. In fact my contribution was fixing lint errors and warnings for a particular subfolder. Sounds pretty straight forward, right?

I was pretty nervous. Will it be approved? Did I do it right? I've fixed errors like this before...

Then, the email dropped in my inbox. I felt like a little kid again. My PR was approved!!

It felt great to reach outside of that comfort zone and make an impact - even if my contribution was small. If someone out there reading this has been nervous to take the plunge, do it! Its rewarding and the community is happy to help.

Building a headless service in Kubernetes

Eddie Hale — Tue, 10 Sep 2019 15:21:50 +0000

Hello! This is my first post to dev.to and excited to be a part of this great community.

A few weeks ago during the development of one of our apps we came across an issue where we needed to communicate with all associated pods instead of load-balancing. Our backend has 7 pods, all with the same image but different secrets to update databases at different locations.

Instead of writing a service for each location and creating a ton of overhead with repetitive yaml files, changing the deployed service to a headless service was the best way to go.

What is a headless service?

A headless service is a service with a service IP but instead of load-balancing it will return the IPs of our associated Pods. This allows us to interact directly with the Pods instead of a proxy. It's as simple as specifying None for .spec.clusterIP and can be utilized with or without selectors - you'll see an example with selectors in a moment.

Check out this sample config:

apiVersion: v1
kind: Service
metadata:
  name: my-headless-service
spec:
  clusterIP: None # <--
  selector:
    app: test-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 3000

See it in action

Create a deployment with five pods.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-deployment
  labels:
    app: api
spec:
  replicas: 5
  selector:
    matchLabels:
      app: api
  template:
    metadata:
      labels:
        app: api
    spec:
      containers:
      - name: api
        image: eddiehale/hellonodeapi
        ports:
        - containerPort: 3000

Create a regular service

apiVersion: v1
kind: Service
metadata:
  name: normal-service
spec:
  selector:
    app: api
  ports:
    - protocol: TCP
      port: 80
      targetPort: 3000

And a headless service

apiVersion: v1
kind: Service
metadata:
  name: headless-service
spec:
  clusterIP: None # <-- Don't forget!!
  selector:
    app: api
  ports:
    - protocol: TCP
      port: 80
      targetPort: 3000

Apply the yaml and verify everything deployed correctly:

$ kubectl apply -f deployment.yaml
$ kubectl get all
NAME                                 READY   STATUS    RESTARTS   AGE
pod/api-deployment-f457fbcf6-6j8f9   1/1     Running   0          5s
pod/api-deployment-f457fbcf6-9gvbp   1/1     Running   0          5s
pod/api-deployment-f457fbcf6-kqbds   1/1     Running   0          5s
pod/api-deployment-f457fbcf6-m76l9   1/1     Running   0          5s
pod/api-deployment-f457fbcf6-qzhxw   1/1     Running   0          5s

NAME                       TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE
service/headless-service   ClusterIP   None             <none>        80/TCP    5s
service/kubernetes         ClusterIP   10.96.0.1        <none>        443/TCP   45h
service/normal-service     ClusterIP   10.109.192.226   <none>        80/TCP    5s

NAME                             READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/api-deployment   5/5     5            5           5s

NAME                                       DESIRED   CURRENT   READY   AGE
replicaset.apps/api-deployment-f457fbcf6   5         5         5       5s

Now that its all running, deploy a Pod and execute a few commands to test.

$ kubectl run --generator=run-pod/v1 --rm utils -it --image eddiehale/utils bash
If you don't see a command prompt, try pressing enter.
root@utils:/#

Lets run nslookup on each service to see what DNS entries exist. If we nslookup normal-service one DNS entry and IP is returned, where nslookup headless-service returns the list of associated Pod IPs with the service DNS:

root@utils:/# nslookup normal-service
Server:         10.96.0.10
Address:        10.96.0.10#53

Name:   normal-service.default.svc.cluster.local
Address: 10.109.192.226

root@utils:/# nslookup headless-service
Server:         10.96.0.10
Address:        10.96.0.10#53

Name:   headless-service.default.svc.cluster.local
Address: 10.1.0.41
Name:   headless-service.default.svc.cluster.local
Address: 10.1.0.39
Name:   headless-service.default.svc.cluster.local
Address: 10.1.0.38
Name:   headless-service.default.svc.cluster.local
Address: 10.1.0.40
Name:   headless-service.default.svc.cluster.local
Address: 10.1.0.37

Clean up

Exit the utils pod:

root@utils:/# exit
exit
Session ended, resume using 'kubectl attach utils -c utils -i -t' command when 
the pod is running
pod "utils" deleted

Delete the services and deployment

$ kubectl delete svc headless-service normal-service && kubectl delete deployment api-deployment
service "headless-service" deleted
service "normal-service" deleted
deployment.extensions "api-deployment" deleted

Headless-services allow us to reach each Pod directly, rather than the service acting as a load-balancer or proxy. This can have many use cases and I'd love to hear your experiences and thoughts in the comments!

Forem: Eddie Hale

My first open source contribution

Building a headless service in Kubernetes

What is a headless service?

See it in action

Clean up