authentication-configmaps-use-case-setting-command-line-arguments.adoc

Setting command-line arguments for container commands with ConfigMaps

A ConfigMap can also be used to set the value of the commands or arguments in a container. This is accomplished by using the Kubernetes substitution syntax $(VAR_NAME). Consider the following ConfigMaps:

apiVersion: v1
kind: ConfigMap
metadata:
  name: special-config
  namespace: default
data:
  special.how: very
  special.type: charm

Procedure

• To inject values into a command in a container, you must consume the keys you want to use as environment variables, as in the consuming ConfigMaps in environment variables use case. Then you can refer to them in a container’s command using the $(VAR_NAME) syntax.

  Sample Pod specification configured to inject specific environment variables

  apiVersion: v1
  kind: Pod
  metadata:
    name: dapi-test-pod
  spec:
    containers:
      - name: test-container
        image: gcr.io/google_containers/busybox
        command: [ "/bin/sh", "-c", "echo $(SPECIAL_LEVEL_KEY) $(SPECIAL_TYPE_KEY)" ] (1)
        env:
          - name: SPECIAL_LEVEL_KEY
            valueFrom:
              configMapKeyRef:
                name: special-config
                key: special.how
          - name: SPECIAL_TYPE_KEY
            valueFrom:
              configMapKeyRef:
                name: special-config
                key: special.type
    restartPolicy: Never

  1. Inject the values into a command in a container using the keys you want to use as environment variables.

     When this Pod is run, the output from the echo command run in the test-container container is as follows:

     very charm