# Lab 2 - Scale Application In this lab, you'll learn how to update the number of instances a deployment has and how to safely roll out an update of your application on Kubernetes. For this lab, you need a running deployment of the `guestbook` application from the previous lab. If you deleted it, recreate it using: ``` kubectl create deployment guestbook --image=ibmcom/guestbook:v1 ``` ## 1. Scale apps with replicas A *replica* is a copy of a pod that contains a running service. By having multiple replicas of a pod, you can ensure your deployment has the available resources to handle increasing load on your application. 1. `kubectl` provides a `scale` subcommand to change the size of an existing deployment. Let's increase our capacity from a single running instance of `guestbook` up to 10 instances: ``` kubectl scale --replicas=10 deployment guestbook ``` Kubernetes will now try to make reality match the desired state of 10 replicas by starting 9 new pods with the same configuration as the first. 2. To see your changes being rolled out, you can run: ``` kubectl rollout status deployment guestbook ``` The rollout might occur so quickly that the following messages might *not* display: ``` $ kubectl rollout status deployment guestbook Waiting for rollout to finish: 1 of 10 updated replicas are available... Waiting for rollout to finish: 2 of 10 updated replicas are available... Waiting for rollout to finish: 3 of 10 updated replicas are available... Waiting for rollout to finish: 4 of 10 updated replicas are available... Waiting for rollout to finish: 5 of 10 updated replicas are available... Waiting for rollout to finish: 6 of 10 updated replicas are available... Waiting for rollout to finish: 7 of 10 updated replicas are available... Waiting for rollout to finish: 8 of 10 updated replicas are available... Waiting for rollout to finish: 9 of 10 updated replicas are available... deployment "guestbook" successfully rolled out ``` 3. Once the rollout has finished, ensure your pods are running by using: ``` kubectl get pods ``` You should see output listing 10 replicas of your deployment: ``` $ kubectl get pods NAME READY STATUS RESTARTS AGE guestbook-562211614-1tqm7 1/1 Running 0 1d guestbook-562211614-1zqn4 1/1 Running 0 2m guestbook-562211614-5htdz 1/1 Running 0 2m guestbook-562211614-6h04h 1/1 Running 0 2m guestbook-562211614-ds9hb 1/1 Running 0 2m guestbook-562211614-nb5qp 1/1 Running 0 2m guestbook-562211614-vtfp2 1/1 Running 0 2m guestbook-562211614-vz5qw 1/1 Running 0 2m guestbook-562211614-zksw3 1/1 Running 0 2m guestbook-562211614-zsp0j 1/1 Running 0 2m ``` **Tip:** Another way to improve availability is to [add clusters and regions](https://cloud.ibm.com/docs/containers?topic=containers-ha_clusters#ha_clusters) to your deployment, as shown in the following diagram: ![HA with more clusters and regions](https://2816711705-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M1Bh2a26msY5M4vW3R9%2Fsync%2F2467d9717f03bd168ee29815ca4aa0c72942bf78.png?generation=1593191663154857\&alt=media) ## 2. Update and roll back apps Kubernetes allows you to do rolling upgrade of your application to a new container image. This allows you to easily update the running image and also allows you to easily undo a rollout if a problem is discovered during or after deployment. In the previous lab, we used an image with a `v1` tag. For our upgrade we'll use the image with the `v2` tag. To update and roll back: 1. Using `kubectl`, you can now update your deployment to use the `v2` image. `kubectl` allows you to change details about existing resources with the `set` subcommand. We can use it to change the image being used. ``` kubectl set image deployment/guestbook guestbook=ibmcom/guestbook:v2 ``` Note that a pod could have multiple containers, each with its own name. Each image can be changed individually or all at once by referring to the name. In the case of our `guestbook` Deployment, the container name is also `guestbook`. Multiple containers can be updated at the same time. ([More information](https://kubernetes.io/docs/reference/generated/kubectl/kubectl-commands#-em-image-em-).) 2. To check the status of the rollout, run: ``` kubectl rollout status deployment/guestbook ``` The rollout might occur so quickly that the following messages might *not* display: ``` $ kubectl rollout status deployment/guestbook Waiting for rollout to finish: 2 out of 10 new replicas have been updated... Waiting for rollout to finish: 3 out of 10 new replicas have been updated... Waiting for rollout to finish: 3 out of 10 new replicas have been updated... Waiting for rollout to finish: 3 out of 10 new replicas have been updated... Waiting for rollout to finish: 4 out of 10 new replicas have been updated... Waiting for rollout to finish: 4 out of 10 new replicas have been updated... Waiting for rollout to finish: 4 out of 10 new replicas have been updated... Waiting for rollout to finish: 4 out of 10 new replicas have been updated... Waiting for rollout to finish: 4 out of 10 new replicas have been updated... Waiting for rollout to finish: 5 out of 10 new replicas have been updated... Waiting for rollout to finish: 5 out of 10 new replicas have been updated... Waiting for rollout to finish: 5 out of 10 new replicas have been updated... Waiting for rollout to finish: 6 out of 10 new replicas have been updated... Waiting for rollout to finish: 6 out of 10 new replicas have been updated... Waiting for rollout to finish: 6 out of 10 new replicas have been updated... Waiting for rollout to finish: 7 out of 10 new replicas have been updated... Waiting for rollout to finish: 7 out of 10 new replicas have been updated... Waiting for rollout to finish: 7 out of 10 new replicas have been updated... Waiting for rollout to finish: 7 out of 10 new replicas have been updated... Waiting for rollout to finish: 8 out of 10 new replicas have been updated... Waiting for rollout to finish: 8 out of 10 new replicas have been updated... Waiting for rollout to finish: 8 out of 10 new replicas have been updated... Waiting for rollout to finish: 8 out of 10 new replicas have been updated... Waiting for rollout to finish: 9 out of 10 new replicas have been updated... Waiting for rollout to finish: 9 out of 10 new replicas have been updated... Waiting for rollout to finish: 9 out of 10 new replicas have been updated... Waiting for rollout to finish: 1 old replicas are pending termination... Waiting for rollout to finish: 1 old replicas are pending termination... Waiting for rollout to finish: 1 old replicas are pending termination... Waiting for rollout to finish: 9 of 10 updated replicas are available... Waiting for rollout to finish: 9 of 10 updated replicas are available... Waiting for rollout to finish: 9 of 10 updated replicas are available... deployment "guestbook" successfully rolled out ``` 1. Test the application as before, by accessing `:` in the browser to confirm your new code is active. Remember, to get the "nodeport" and "public-ip" use the following commands. Replace `$CLUSTER_NAME` with the name of your cluster if the environment variable is not set.: ``` kubectl describe service guestbook ``` and ``` ibmcloud ks workers --cluster $CLUSTER_NAME ``` To verify that you're running "v2" of guestbook, look at the title of the page, it should now be `Guestbook - v2`. If you are using a browser, make sure you force refresh (invalidating your cache). 2. If you want to undo your latest rollout, use: ``` kubectl rollout undo deployment guestbook ``` You can then use this command to see the status: ``` kubectl rollout status deployment/guestbook ``` 3. When doing a rollout, you see references to *old* replicas and *new* replicas. The *old* replicas are the original 10 pods deployed when we scaled the application. The *new* replicas come from the newly created pods with the different image. All of these pods are owned by the Deployment. The deployment manages these two sets of pods with a resource called a ReplicaSet. We can see the guestbook ReplicaSets with: ``` $ kubectl get replicasets -l app=guestbook NAME DESIRED CURRENT READY AGE guestbook-5f5548d4f 10 10 10 21m guestbook-768cc55c78 0 0 0 3h ``` Before we continue, let's delete the application so we can learn about a different way to achieve the same results: To remove the deployment, use ``` kubectl delete deployment guestbook ``` To remove the service, use: ``` kubectl delete service guestbook ``` Congratulations! You deployed the second version of the app. Lab 2 is now complete. Continue to the [next lab of this course](https://ibm-developer.gitbook.io/cloudpakforapplications-appmod/technology-foundations/kube101/lab3).