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Inject Sidecar Container with SidecarSet

The sidecarset controller implements a MutatingAdmissionWebhook which watches for Pod creation and automatically injects the containers specified in sidecarset CRDs into the matched pods. This tutorial demonstrates how sidecarset controller automatically injects a guestbook sidecar container for gusetbook Pods.

Install guestbook sidecarset

kubectl apply -f https://raw.githubusercontent.com/kruiseio/kruise/master/docs/tutorial/v1/guestbook-sidecar.yaml

guestbook-sidecar at a glance

apiVersion: apps.kruise.io/v1alpha1
kind: SidecarSet
metadata:
  name: guestbook-sidecar
spec:
  selector: # select the pods to be injected with sidecar containers
    matchLabels:
      app.kubernetes.io/name: guestbook-with-sidecar
  containers:
    - name: guestbook-sidecar
      image: openkruise/guestbook:sidecar
      imagePullPolicy: Always
      ports:
        - name: sidecar-server
          containerPort: 4000 # different from main guestbook containerPort which is 3000
      volumeMounts:
        - name: log-volume
          mountPath: /var/log
  volumes:
    - name: log-volume
      emptyDir: {}

Install guestbook application

Run following command to install the helm chart with release name (application name) of demo-v1, replica of 20:

helm install demo-v1 apphub/guestbook-kruise --set replicaCount=20,image.repository=openkruise/guestbook,image.tag=v2 nameOverride=guestbook-with-sidecar

Alternatively, install the application using YAML files:

kubectl apply -f https://raw.githubusercontent.com/kruiseio/kruise/master/docs/tutorial/v1/guestbook-sts-for-sidecar-demo.yaml
kubectl apply -f https://raw.githubusercontent.com/kruiseio/kruise/master/docs/tutorial/v1/guestbook-service-for-sidecar-demo.yaml

Check guestbook Pod containers

Run kubectl get sts.apps.kruise.io to check the statefulset status. Note that statefulset.apps.kruise.io or shortname sts.apps.kruise.io is the resource kind. app.kruise.io postfix is needed to resolve the naming conflict with Kubernetes native statefulset kind. Verify that all pods are READY.

NAME                        DESIRED    CURRENT    UPDATED    READY    AGE
guestbook-with-sidecar      20         20         20         20       17s

Run kubectl get pod to check the status of all replicas.

NAME                        READY   STATUS    RESTARTS   AGE
guestbook-with-sidecar-0    2/2     Running   0          18s
guestbook-with-sidecar-1    2/2     Running   0          18s
...
guestbook-with-sidecar-17   2/2     Running   0          13s
guestbook-with-sidecar-18   2/2     Running   0          13s
guestbook-with-sidecar-19   2/2     Running   0          12s

Run kubectl describe pod guestbook-with-sidecar-0 to check one Pod and verify that the sidecar container is injected.

    Containers:
      guestbook:
        Container ID:   docker://44f19a140c30de2c5b1a3f63c252c074efbb9c1b5eb7893ee7134461466b35c8
        Image:          openkruise/guestbook:v2
        Image ID:       docker-pullable://openkruise/guestbook@sha256:a5b6e5462982ca795fa9c7ddc378ea5b24a31e5d57eb806095526f7b21384dbd
        Port:           3000/TCP
        Host Port:      0/TCP
        State:          Running
          Started:      Wed, 19 Jun 2019 17:30:29 +0800
        Ready:          True
        Restart Count:  0
        Environment:    <none>
        Mounts:
          /var/run/secrets/kubernetes.io/serviceaccount from default-token-k5qpw (ro)
+     guestbook-sidecar:
+       Container ID:   docker://cbc379ce84624d9801928d5b2f1f2739e24094b440c55d62f7e0892eb31b0719
+       Image:          openkruise/guestbook:sidecar
+       Image ID:       docker-pullable://openkruise/guestbook@sha256:016eddf673cc7afc5da2fa96b5148161b521cff20583fb1d0c3aa44e6ac75272
+       Port:           4000/TCP
+       Host Port:      0/TCP
+       State:          Running
+         Started:      Wed, 19 Jun 2019 17:30:45 +0800
+       Ready:          True
+       Restart Count:  0
+       Environment:
+         IS_INJECTED:  true
+       Mounts:
+         /var/log from log-volume (rw)

Access the Sidecar service

Now you can access the Sidecar guestbook service via web browser.

  • Local Host: If you are running all Kubernetes components locally in a single node, navigate to http://localhost:4000 to access the sidecar service.

  • Remote Host: To access the sidecar service on a remote host, run kubectl get services and find the external IP of the service in the EXTERNAL-IP column of the output. e.g., 47.101.74.131 in this example.

NAME                      TYPE           CLUSTER-IP     EXTERNAL-IP     PORT(S)                         AGE
guestbook-with-sidecar    LoadBalancer   172.21.2.187   47.101.74.131   3000:31459/TCP,4000:32099/TCP   35m

The web browser output looks like: Guestbook

The main guestbook service is running on port 3000, e.g., http://localhost:3000. Check for the difference!

In above example, the guestbook-with-sidecar service uses LoadBalancer type. It works in a cloud environment where cloud provider supports external load balancers. In case one wants to examine the same in local environment using minikube, change the guestbook-with-sidecar service type to NodePort. An example guestbook-service-for-sidecar-demo.yaml looks like:

apiVersion: v1
kind: Service
metadata:
  name: guestbook-with-sidecar
  labels:
    app: guestbook-with-sidecar
spec:
  ports:
  - nodePort: 30163
    port: 3000
    targetPort: http-server
    name: main-port
  - nodePort: 30164
    port: 4000
    targetPort: sidecar-server
    name: sidecar-port
  selector:
    app.kubernetes.io/name: guestbook-with-sidecar
  type: NodePort

Relaunch the guestbook-with-sidecar service, then one can navigate http://MINIKUBE_IP:30164 to access the sidecar service.

Update the sidecar

Use kubectl edit sidecarset guestbook-sidecar, change image to "openkruise/guestbook:sidecar-v2"

Use kubectl get sidecarset guestbook-sidecar, check if all pods are updated according to UPDATED field

When all pods are updated, visit http://47.101.74.131:4000 again Guestbook2

Clean up

Using helm to uninstall apps is very easy.

First you may want to list your helm apps:

helm list
NAME          NAMESPACE  REVISION  UPDATED                               STATUS    CHART
demo-v1       default    1         2019-06-23 13:33:21.278013 +0800 CST  deployed  guestbook-kruise-0.3.0

Then uninstall it:

helm uninstall demo-v1

If you are not using helm, deleting the application using below commands:

kubectl delete sts.apps.kruise.io guestbook-with-sidecar
kubectl delete svc guestbook-with-sidecar
kubectl delete sidecarset guestbook-sidecar