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Configuration Resource

To try out this example, ensure you have access to a Kubernetes cluster by choosing one of the options from INSTALL.

The sample [random-generator] REST service can be configured using environment variables and an application.properties configuration file. In this example, we’ll provide this configuration via a ConfigMap.

First, create the ConfigMap with the following command:

kubectl apply -f https://k8spatterns.io/ConfigurationResource/configmap.yml

Next, the following Pod declaration will use this ConfigMap as environment variables and mount the application.properties entry as random-generator.properties in the /config/app directory.

For additional explanations, please review the comments at pod.yml.

Create the Pod with this command:

kubectl create -f https://k8spatterns.io/ConfigurationResource/pod.yml

As in previous examples, we’ll expose a nodePort service for accessing our service:

kubectl apply -f https://k8spatterns.io/ConfigurationResource/service.yml

Now, access the service, assuming your cluster node has an external IP address that can be directly contacted from your desktop.

The /info endpoint returns the configuration data picked up by the random-generator Pod:

minikube service random-generator --url > /tmp/random-url.txt &

This command starts a tunnel in the background and writes down the access URLs for the exposed ports. Store these URLs in a text file and use the following command to access the service:

curl -s $(cat /tmp/random-url.txt)/info | jq .

To filter the environment variables that have been bulk-exposed with a CONFIG_ prefix in an envFrom section, use:

curl -s $(cat /tmp/random-url.txt)/info | \
   jq '.env | with_entries(select(.key | startswith("CONFIG_")))'

Now let’s check whether the permissions of the mounted random-generator.properties file has been set properly to 0400; use the following command:

kubectl exec random-generator -- ls -l /config/app/random-generator.properties

Finally, to demonstrate that the ConfigMap is indeed immutable, attempt to patch it with the following command:

kubectl patch configmap random-generator-config --type merge -p '{"data":{"newKey":"newValue"}}'

You should receive an error indicating that the ConfigMap cannot be updated since it is marked as immutable.