(DEPRECATED) Update an application in Kubernetes

After an application has been deployed in Kubernetes, it can be updated by specifying a new container image or image version. When doing so, the update is staged so that only a portion of the deployment is concurrently updated. This staged update enables the application to keep running during the update. It also provides a rollback mechanism if a deployment failure occurs.

In this tutorial, part six of seven, the sample Azure Vote app is updated. Tasks that you complete include:

In subsequent tutorials, Log Analytics is configured to monitor the Kubernetes cluster.

Before you begin

In previous tutorials, an application was packaged into a container image, the image uploaded to Azure Container Registry, and a Kubernetes cluster created. The application was then run on the Kubernetes cluster.

An application repository was also cloned which includes the application source code, and a pre-created Docker Compose file used in this tutorial. Verify that you have created a clone of the repo, and that you have changed directories into the cloned directory. Inside is a directory named azure-vote and a file named docker-compose.yml.

If you haven't completed these steps, and want to follow along, return to Tutorial 1 – Create container images.

Update application

For this tutorial, a change is made to the application, and the updated application deployed to the Kubernetes cluster.

The application source code can be found inside of the azure-vote directory. Open the config_file.cfg file with any code or text editor. In this example vi is used.

vi azure-vote/azure-vote/config_file.cfg

Change the values for VOTE1VALUE and VOTE2VALUE, and then save the file.

# UI Configurations
TITLE = 'Azure Voting App'
VOTE1VALUE = 'Blue'
VOTE2VALUE = 'Purple'
SHOWHOST = 'false'

Save and close the file.

Update container image

Use docker-compose to re-create the front-end image and run the updated application. The --build argument is used to instruct Docker Compose to re-create the application image.

docker-compose up --build -d

Test application locally

Browse to https://localhost:8080 to see the updated application.

Tag and push images

Tag the azure-vote-front image with the loginServer of the container registry.

Get the login server name with the az acr list command.

az acr list --resource-group myResourceGroup --query "[].{acrLoginServer:loginServer}" --output table

Use docker tag to tag the image. Replace <acrLoginServer> with your Azure Container Registry login server name or public registry hostname. Also notice that the image version is updated to redis-v2.

docker tag azure-vote-front <acrLoginServer>/azure-vote-front:redis-v2

Use docker push to upload the image to your registry. Replace <acrLoginServer> with your Azure Container Registry login server name.

docker push <acrLoginServer>/azure-vote-front:redis-v2

Deploy update application

To ensure maximum uptime, multiple instances of the application pod must be running. Verify this configuration with the kubectl get pod command.

kubectl get pod

Output:

NAME                               READY     STATUS    RESTARTS   AGE
azure-vote-back-217588096-5w632    1/1       Running   0          10m
azure-vote-front-233282510-b5pkz   1/1       Running   0          10m
azure-vote-front-233282510-dhrtr   1/1       Running   0          10m
azure-vote-front-233282510-pqbfk   1/1       Running   0          10m

If you do not have multiple pods running the azure-vote-front image, scale the azure-vote-front deployment.

kubectl scale --replicas=3 deployment/azure-vote-front

To update the application, use the kubectl set command. Update <acrLoginServer> with the login server or host name of your container registry.

kubectl set image deployment azure-vote-front azure-vote-front=<acrLoginServer>/azure-vote-front:redis-v2

To monitor the deployment, use the kubectl get pod command. As the updated application is deployed, your pods are terminated and re-created with the new container image.

kubectl get pod

Output:

NAME                               READY     STATUS    RESTARTS   AGE
azure-vote-back-2978095810-gq9g0   1/1       Running   0          5m
azure-vote-front-1297194256-tpjlg   1/1       Running   0         1m
azure-vote-front-1297194256-tptnx   1/1       Running   0         5m
azure-vote-front-1297194256-zktw9   1/1       Terminating   0         1m

Test updated application

Get the external IP address of the azure-vote-front service.

kubectl get service azure-vote-front

Browse to the IP address to see the updated application.

Next steps

In this tutorial, you updated an application and rolled out this update to a Kubernetes cluster. The following tasks were completed:

Advance to the next tutorial to learn about how to monitor Kubernetes with Log Analytics.