Node Express Kubernetes Example

Simple NodeJS application to explain basic parts of Kubernetes.

Run simple Node.js application in Kubernetes cluster (DigitalOcean)

Routes

The /app-id route returns random string generated on application start, so that user can see if he is connecting to different pods (containers).

{"appId":"1.13.647"}

Another request should return a different number in the end.

{"appId":"1.13.539"}

The /evn/:name route returns environment variable as a proof that the application has access to values passed from Kubernetes Secret. For example you can try /env/secretParameter.

{"secretParameter":"DatabaseCredentials"}

Test readiness probe

If starting of a pod can take some time, you can define a readinessProbe. This is also usable if the pod has some unfinished work and is not available to receive any other requests. The check in this case is set to http get, so if it returns http status code 200 kubernetes will include the pod and if it returns status code 500 it will exclude the pod.

You can test it by refreshing the page and checking the appId and then visit http://<IP address>/ready/toggle, which will toggle the readiness for 10 seconds. During this time one of the app ids should not occure again.

Test liveness probe

If some fatal error occured or something else that actually blocked the whole process and the app is basically dead, the livenessProbe check detects it and restarts the pod. To see this in action, you need to check pods:

kubectl get pods

This will return:

NAME                                                 READY   STATUS    RESTARTS   AGE
node-docker-kubernetes-deployment-78f7d56b4b-2sg69   1/1     Running   0          5m37s
node-docker-kubernetes-deployment-78f7d56b4b-d8n9h   1/1     Running   0          5m26s

If you visit http://<IP address>/alive/toggle and refresh the app a few times, one of the ids should not occure for a while. And if you check the pods again, the restarts info in one of the pods should show you 1:

NAME                                                 READY   STATUS    RESTARTS   AGE
node-docker-kubernetes-deployment-78f7d56b4b-2sg69   1/1     Running   1          5m37s
node-docker-kubernetes-deployment-78f7d56b4b-d8n9h   1/1     Running   0          5m26s

Test

let number = 0;

const load = async () => {
  return fetch('https://node-test.kontentinoservices.dev/app-id')
    .then(response => response.json())
    .then((data) => {
      console.log(`${number} App ID: ${data.appId}`);
    });
}

const sleep = async (ms) => {
  return new Promise((resolve) => {
    setTimeout(resolve, ms);
  });
}

while (true) {
  number++;
  await load();
  await sleep(1000);
}

License

MIT license