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Application Configuration via ConfigMaps

In this example, we will deploy an app called my-app and it will read the application configuration from a ConfigMap.

Change into the lab directory:

cd /workspaces/kubernetes-fundamentals-for-devs/01_configmaps

INGRESS_IP environment variable is supposed to be set during the setup. You can always set it this way:

export INGRESS_IP=$(kubectl get svc ingress-nginx-controller -n ingress-nginx -o jsonpath='{.status.loadBalancer.ingress[].ip}')

Configure the Application via ConfigMap

Apply the manifests:

kubectl apply -f k8s/

Check the output of the application

curl http://${INGRESS_IP}/my-app

# output:
# <!DOCTYPE html><htlml><body>Message: Message from ConfigMap<br>Pod Name: <br>Pod IP: <br>Live: true<br>Ready: true<br></body></htlml>

If you want to reach it via browser, you first need to port-forward ingress-nginx-controller service:

kubectl port-forward svc/ingress-nginx-controller -n ingress-nginx 80

Then, reach via below URLs:

echo "https://${CODESPACE_NAME}-80.app.github.dev/my-app"

Note that the the message is taken from the ConfigMap and not from the containers default configuration file for the application.

Changing the ConfigMap

Change the message of the ConfigMap k8s/configmap.yaml

data: 
  app.conf: |-
    message = Some different message

Apply the change in the ConfigMap.

kubectl apply -f k8s/configmap.yaml

or run the below command:

kubectl patch cm my-configmap -p '{"data": {"app.conf": "message = Some different message"}}'

Note: ConfigMap changes will not be reflected automatically. You need to restart the pod. (In this case, recreate/replace). You can get into tricky situations eg on deploying stuff via Helm Charts.

# restart the pod
kubectl replace -f k8s/pod.yaml --force

# verify that the message is updated
curl http://${INGRESS_IP}/my-app

If you want to reach it via browser, you first need to port-forward ingress-nginx-controller service:

kubectl port-forward svc/ingress-nginx-controller -n ingress-nginx 80

Then, reach via below URLs:

echo "https://${CODESPACE_NAME}-80.app.github.dev/my-app"

Additional Information

There are some automated ways to restart your applications after ConfigMap/Secret changes. For example:

  1. Kyverno Policy: Restart Deployment on a Secret Change
  2. Helm: Automatically Roll Deployments

Cleanup

kubectl delete -f k8s/