Create step9.md

Author: Splaktar

step9.md

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+# 9. Roll out an upgrade to your app
+
+Estimated time: 13 min remaining
+
+As always, the application you deployed to production requires bug fixes or additional features. 
+Kubernetes is here to help you deploy a new version to production without impacting your users.
+
+First, let’s modify the application. In the cloud console, edit `server.js` and update the response message:
+```javascript
+response.end("Hello Kubernetes World!");
+```
+
+We can now build and publish a new container image to the registry with an incremented tag:
+```sh
+$ docker build -t gcr.io/PROJECT_ID/hello-node:v2 . 
+$ gcloud docker push gcr.io/PROJECT_ID/hello-node:v2
+```
+
+**Note**: Building and pushing this updated image should be much quicker as we take full advantage of the Docker cache.
+
+We’re now ready for kubernetes to smoothly update our replication controller to the new version of the application:
+```sh
+$ kubectl rolling-update hello-node \
+    --image=gcr.io/PROJECT_ID/hello-node:v2 \
+    --update-period=2s
+Creating hello-node-324d23dd3e0e2474d6b76dc599abb519
+At beginning of loop: hello-node replicas: 2, hello-node-324d23dd3e0e2474d6b76dc599abb519 replicas: 1
+...
+At end of loop: hello-node replicas: 0, hello-node-324d23dd3e0e2474d6b76dc599abb519 replicas: 3
+Update succeeded. Deleting old controller: hello-node
+Renaming hello-node-324d23dd3e0e2474d6b76dc599abb519 to hello-node
+hello-node
+```
+You should see in the standard output how the rolling update actually works:
+
+1. A new replication controller is created based on the new image
+1. The replica count on the new and old controllers is increased/decreased by one respectively until the desired number of 
+replicas is reached
+1. The original replication controller is deleted
+
+While this is happening, the users of the services should not see any interruption. After a little while they will start
+accessing the new version of your application. You can find more details on rolling updates in 
+[this documentation](https://cloud.google.com/container-engine/docs/rolling-updates).
+
+Hopefully with these deployment, scaling and update features you’ll agree that once you’ve setup your environment (your GKE/Kubernetes cluster here), Kubernetes is here to help you focus on the application rather than the infrastructure.
+
+#### [Go to step 10](step10.md)
+#### [Go back to step 8](step8.md)