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Kubernetes ConfigMap Notes

Using ConfigMaps as Environment Variables​

Single environment variable from ConfigMap​

env:
  - name: CONFIGMAP_USERNAME
    valueFrom:
      configMapKeyRef:
        name: myconfigmap
        key: username

All keys from ConfigMap as environment variables​

envFrom:
  - configMapRef:
      name: myconfigmap

[!IMPORTANT] ConfigMaps consumed as environment variables are NOT updated automatically and require a pod restart to reflect changes.

Using ConfigMaps as Volumes​

Basic volume mount​

volumes:
  - name: foo
    configMap:
      name: myconfigmap

volumeMounts:
  - name: foo
    mountPath: "/etc/foo"
    readOnly: true

Mounting specific keys as files​

volumes:
  - name: config
    configMap:
      name: game-demo
      items:
        - key: "game.properties"
          path: "game.properties"
        - key: "user-interface.properties"
          path: "user-interface.properties"

Note: If you omit the items array entirely, every key in the ConfigMap becomes a file with the same name as the key.

How volume mounting works​

  1. Define Volumes: Set volumes at the Pod level (.spec.volumes[])
  2. Reference ConfigMap: Set .spec.volumes[].configMap.name to reference your ConfigMap
  3. Container Mount: Add .spec.containers[].volumeMounts[] to each container that needs the data
  4. Security: Specify .spec.containers[].volumeMounts[].readOnly = true
  5. Pathing: Set .spec.containers[].volumeMounts[].mountPath to an unused directory name
  6. File Creation: Each key in the ConfigMap data map becomes a filename under the specified mountPath

ConfigMap Updates​

MethodUpdate Behavior
Volume MountsProjected keys are eventually updated automatically after the ConfigMap is modified
subPath MountsA container using a ConfigMap as a subPath volume mount will NOT receive updates
Environment VarsThese are NOT updated automatically and require a pod restart

Immutable ConfigMaps​

Making a ConfigMap immutable​

apiVersion: v1
kind: ConfigMap
metadata:
  name: my-immutable-config
immutable: true
data:
  key: value

Important notes about immutability​

  • Permanent: Once a ConfigMap is marked as immutable, it is NOT possible to revert this change
  • Locked Data: You cannot mutate the contents of the data or binaryData fields
  • Recreation: To change values, you must delete and recreate the ConfigMap
  • Performance: Immutability significantly reduces the load on the API server by closing watches for these resources