Lab K104 - Adding HA and Scalability with Replication Controllers
If you are not running a monitoring screen, start it in a new terminal with the following command.
watch -n 1 kubectl get pod,rc
Adding Replication Controller Configurations
Lets now write the spec for the Replication Controller . This is going to mainly contain,
- template (pod spec )
From here on, we would switch to the project and environment specific path and work from there.
edit file: vote-rc.yaml
apiVersion: xxx kind: xxx metadata: xxx spec: xxx template: metadata: name: vote labels: app: python role: vote version: v1 spec: containers: - name: app image: schoolofdevops/vote:v1 resources: requests: memory: "64Mi" cpu: "50m" limits: memory: "128Mi" cpu: "250m"
Above file already containts the spec that you had written for the pod. You would observe its already been added as part of spec.template for Replication Controller.
Lets now add the details specific to Replication Controller.
apiVersion: apps/v1 kind: ReplicationController metadata: name: vote spec: minReadySeconds: 20 replicas: 4 selector: role: vote template: metadata: name: vote labels: app: python role: vote version: v1 spec: containers: - name: app image: schoolofdevops/vote:v1 resources: requests: memory: "64Mi" cpu: "50m" limits: memory: "128Mi" cpu: "250m"
The complete file will look similar to above. Lets now go ahead and apply it.
kubectl apply -f vote-rc.yaml --dry-run kubectl apply -f vote-rc.yaml kubectl get rc kubectl describe rc vote kubectl get pods kubectl get pods --show-labels
Try deleting pods created by the Replication Controller,
replace pod-xxxx and pod-yyyy with actuals
kubectl get pods kubectl delete pods vote-xxxx vote-yyyy
Observe as the pods are automatically created again.
Lets now delete the pod created independent of replication controller.
kubectl get pods kubectl delete pods vote
Observe what happens. * Does replica set take any action after deleting the pod created outside of its spec ? Why?
Exercise: Deploying new version of the application
kubectl edit rc/vote
Update the version of the image from schoolofdevops/vote:v1 to schoolofdevops/vote:v2
Save the file.
Observe what happens ?
- Did application get updated.
- Did updating Replication Controller launched new pods to deploy new version ?
Scaling up application is as easy as running,
kubectl scale --replicas=8 rc/vote kubectl get pods --show-labels
Observe what happens
- Did the number of replicas increase to 8 ?
- Which version of the app are the new pods running with ?
With Replication Controllers your application is now high available as well as scalable. However Replication Controller by itself does not have the intelligence to trigger a rollout if you update the version. For that, you are going to need a deployment which is something you would learn in an upcoming lesson.