Kubernetes - Sidecar Containers in a Pod

Prerequisites

• Kubernetes
• kubectl

Assignment

• Lets start by creating a pod which will have a sidecar container which will print ‘hello’ every 5 seconds

1️⃣ Create a K8 manifest yaml to deploy a pod with two containers.

cat <<EOF > ./sidecar-container-demo.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: mypod
  name: mypod
spec:
  containers:
  - name: webserver
    image: nginx
    resources: {}
  - name: sidecar
    image: ubuntu
    args:
    - /bin/sh
    - -c
    - |
      while true; do
        echo "$(date +'%T') — Hello from the sidecar";
        sleep 5;
        if [ -f /tmp/crash ]; then exit 1; fi;
      done
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}
EOF

2️⃣ Create a pod using the manifest file

```sh
kubectl apply -f ./sidecar-container-demo.yaml
```

3️⃣ Verify that the pod was created and check the number of containers under Ready column

```sh
kubectl get pods -o wide
```

4️⃣ Use the describe command to verify that the pod has 2 containers

```sh
kubectl describe pod/mypod
```

5️⃣ Run another pod to verify that the mypod is working as expected

```sh
kubectl run -it --rm --image=curlimages/curl --restart=Never curl -- http://<pod-ip>
```

6️⃣ Verify if the sidecar is generating logs as per the instructions

```sh
kubectl logs pod/mypod -c sidecar
```

7️⃣ Crash the sidecar container and verify the pod status. You will notice that pod has restarted once and is now in running state as per the restartPolicy.

```sh
kubectl exec -it mypod -c sidecar -- touch /tmp/crash
```

```sh
kubectl get pods
```

8️⃣ Check the logs of the sidecar container which was intentionally crashed (you can check the timestamps to identify the issue. You wont see any error in this example)

```sh
kubectl logs pod/mypod -c sidecar --previous
```

Clean-Up

kubectl delete -f ./sidecar-container-demo.yaml --now
rm ./sidecar-container-demo.yaml