What is a ConfigMap in Kubernetes?

Today, in the world of application development, it’s recommended to separate the configuration from the code. Kubernetes’ ConfigMaps helps us do this.

Create a ConfigMap

ConfigMap allows you to define key and values or a properties file that can be used either at startup of the pod, or as a mount on the pod.

	apiVersion: v1
	kind: ConfigMap
	metadata:
	name: example-config
	data:
	# property-like keys; each key maps to a simple value
	"license": "XXXX"
	"licensedto": "dummy"
	# file-like keys
	app.properties: |
	key1=value1
	key2=value2

view raw cmcreate.yaml hosted with ❤ by GitHub

Uses of ConfigMap

We can use the ConfigMap for configuration inside a pod in the following ways:

• Using commands and arguments inside a container.
• Using environment variables for a container
• Adding the ConfigMaps as a file in read-only volume, from where the application can read.
• Using the Kubernetes API in the code running inside the container that can read the configmap.

Example

Here, we load the ConfigMaps values during pod initialization as environment variables.

	apiVersion: v1
	kind: Pod
	metadata:
	name: configmap-example-pod
	spec:
	containers:
	– name: example-container
	image: alpine
	command: ["sleep", "3600"]
	env:
	# Define the environment variable
	– name: LICENSE # Environment Variable name, can be different from configmap key
	valueFrom:
	configMapKeyRef:
	name: example-config # The ConfigMap this value comes from.
	key: license # The key to fetch.

view raw cmload.yaml hosted with ❤ by GitHub

Mount ConfigMap as a file in read-only volume

Following is an example of how to use values from a ConfigMap at the time of container initialization:

	apiVersion: v1
	kind: Pod
	metadata:
	name: configmap-demo-pod
	spec:
	containers:
	– name: demo
	image: alpine
	command: ["sleep", "3600"]
	volumeMounts:
	– name: config
	mountPath: "/config"
	readOnly: true
	volumes:
	– name: config
	configMap:
	name: example-config

view raw mountcm.yaml hosted with ❤ by GitHub

Volumes are set at the pod level, then mounted into containers inside that pod. The mounted configuration maps are updated automatically when the value in the `ConfigMap` changes.

Conclusion

ConfigMaps are a great mechanism to set up configurations separate from code. The configurations are updated automatically and redeployment is not required.

Note: The above does not hold true if the ConfigMap is marked as immutable.