OSGi Kubernetes example

This example shows how to create a small OSGi based application and deploy it to kubernetes.

Prerequisites

Install

• jdk 1.8
• maven >= 3.5
• docker

Source

Checkout the source

git clone git@github.com:cschneider/osgi-example-kubernetes.git

Start eclipse and import from top level directory as existing maven projects.

Build

mvn clean install

Run standalone

java -jar starter/target/app.jar

Access the deployment

http://localhost:8080/hello

This should return Hello World and is served by a JAX-RS service.

http://localhost:8080/systemready

Returns the ready state of the system. At the start this might return YELLOW but after a very short while it should return GREEN.

http://localhost:8080/system/console

Allows access to the felix webconsole to look into all details of the system.

Run in Kubernetes

You need access to a kubernetes cluster. To achieve this either install minikube or get a kubernetes cluster from a cloud provider.

For my tests I installed the kubernetes service on Azure. This only needs a few clicks. The default settings work fine.

This does a maven build plus docker container creation and docker push.

sh build.sh

Deploy to your kubernetes Cluster

kubectl apply -f example-kubernetes

This installs the docker container as a deployment with one instance. Additionally it creates a service with a load balancer.

Check the deployment worked

kubectl get pods

 It should display output like below. We should have one pod installed that
 contains our OSGi app.

 NAME                                  READY     STATUS    RESTARTS   AGE
 example-kubernetes-6b7985c88f-tcfmh   1/1       Running   0          10h

 kubectl get services

 Here we should see a service that makes our example available on an external
 ip with a load balancer.

 NAME                 TYPE           CLUSTER-IP    EXTERNAL-IP      PORT(S)          AGE
 example-kubernetes   LoadBalancer   10.0.207.16   104.211.55.231   8080:30215/TCP   22h

Now test the steps from "access the deployment" above with your external IP instead of localhost.

Update kubernetes deployment

Change some code.

Then do

sh build.sh
kubectl delete pod -l run=example-kubernetes

This builds and deploys the new docker image and then deletes all existing pods. This will cause kubernetes to spawn a new pod which loads the new image.

Test liveness

Our example is deployed in kubernetes with a liveness check. If this check fails then kubernetes will restart the pod.

To see current pods run this in a shell. It will wait and display changes.

kubectl get pods -o wide -w

Now let's report not alive:

http://cschneid.eastus.cloudapp.azure.com:8080/control/notalive

After a few seconds we should see the number of restarts increase in the shell where we check for the pods. Alternatively you can use the kubernetes dashboard and look into the running pod. It will show failed readiness and liveness checks and report that the instance will be killed and restarted.

Test readiness

Our example is deployed in kubernetes with a liveness check. If this check fails then kubernetes will restart the pod.

To see current pods run this in a shell. It will wait and display changes.

kubectl get pods -o wide -w

Focus on the ready column. It should report "1/1".

Now let's report not ready for 60 seconds:

http://cschneid.eastus.cloudapp.azure.com:8080/control/notready

Then quickly check the ready probe:

http://cschneid.eastus.cloudapp.azure.com:8080/systemready

It will now report RED. Keep an eye on the pod list above. It should update with "0/1" in the ready column. Once kubernetes consideres the pod as not ready it will take it out of the load balancer. So when we check the ready state above again it will not respond.

After the 60 seconds it should go back to "1/1". The ready state in our probe will return to GREEN.

Further experimentation

Scale the deployment to 2 intances and check how the cluster now behaves.

kubectl scale deployments/example-kubernetes --replicas=2