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Init Container

In this example we will see a simple Init Container in action. As in the other examples we assume that you have a running Kubernetes cluster to your avail. Checkout INSTALL documentation for some options to access a Kubernetes cluster.

In this example we are creating a Pod with an init container and a main container:

  • The Init Container will start first and checks out a GitHub repository containing a static example web site.

  • The application container started after the Init Container has finished will then serve these pages over port 80

Let’s create this bare Pod into the current namespace with:

kubectl create -f https://k8spatterns.io/InitContainer/pod.yml

Check the startup of the pod by watching the pod by executing the following command right after the creation of your Pod:

kubectl get pods -w

You will see some output like

NAME   READY   STATUS            RESTARTS   AGE
www    0/1     Init:0/1          0          8s
www    0/1     PodInitializing   0          10s
www    1/1     Running           0          12s

Finally, let’s check how we can access the data that had been retrieved by the Init Container. For this we create a nodePort Service with

kubectl create -f https://k8spatterns.io/InitContainer/service.yml

This will open the a port on every node of which we can access the static HTTP server.

With a little Json path foo we can extract that dynamically assigned port and curl the web page or open it in a web browser:

port=$(kubectl get svc www -o jsonpath={.spec.ports[0].nodePort})
# If using Minishift:
ip=$(minikube ip)
# or set ip to your real cluster's address (e.g. obtained from `kubectl cluster-info`)
curl -s http://$ip:$port

If this access doesn’t work it could be that your cluster doesn’t allow access to your node’s ports directly. In this case either use e.g. Minikube which allows that or use a different service access as described in the pattern "Service Discovery".