15.4. Use Cases: Consuming ConfigMaps in pods

The following sections describe some uses cases when consuming ConfigMap objects in pods.

15.4.1. Populating environment variables in containers by using config maps

Config maps can be used to populate individual environment variables in containers or to populate environment variables in containers from all keys that form valid environment variable names.

As an example, consider the following config map:

ConfigMap with two environment variables

apiVersion: v1
kind: ConfigMap
metadata:
  name: special-config 1
  namespace: default 2
data:
  special.how: very 3
  special.type: charm 4

1
Name of the ConfigMap.
2
The project in which the ConfigMap resides. Config maps can only be referenced by pods in the same project.
3 4
Environment variables to inject.

ConfigMap with one environment variable

apiVersion: v1
kind: ConfigMap
metadata:
  name: env-config 1
  namespace: default
data:
  log_level: INFO 2

1
Name of the ConfigMap.
2
Environment variable to inject.

Procedure

  • You can consume the keys of this ConfigMap in a pod using configMapKeyRef sections.

    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", "env" ]
      env: 1
        - name: SPECIAL_LEVEL_KEY 2
          valueFrom:
            configMapKeyRef:
              name: special-config 3
              key: special.how 4
        - name: SPECIAL_TYPE_KEY
          valueFrom:
            configMapKeyRef:
              name: special-config 5
              key: special.type 6
              optional: true 7
      envFrom: 8
        - configMapRef:
            name: env-config 9
  restartPolicy: Never

    1
    Stanza to pull the specified environment variables from a ConfigMap.
    2
    Name of a Pod environment variable that you are injecting a key’s value into.
    3 5
    Name of the ConfigMap to pull specific environment variables from.
    4 6
    Environment variable to pull from the ConfigMap.
    7
    Makes the environment variable optional. As optional, the Pod will be started even if the specified ConfigMap and keys do not exist.
    8
    Stanza to pull all environment variables from a ConfigMap.
    9
    Name of the ConfigMap to pull all environment variables from.

    When this Pod is run, the Pod logs will include the following output: 

    SPECIAL_LEVEL_KEY=very
log_level=INFO
注意

SPECIAL_TYPE_KEY=charm is not listed in the example output because optional: true is set.

15.4.2. 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

15.4.3. Injecting content into a volume by using config maps

You can inject content into a volume by using config maps.

Example ConfigMap

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

Procedure

You have a couple different options for injecting content into a volume by using config maps.

  • The most basic way to inject content into a volume by using a config map is to populate the volume with files where the key is the file name and the content of the file is the value of the key: 

    apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  containers:
    - name: test-container
      image: gcr.io/google_containers/busybox
      command: [ "/bin/sh", "cat", "/etc/config/special.how" ]
      volumeMounts:
      - name: config-volume
        mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
        name: special-config 1
  restartPolicy: Never
    1
    File containing key.

    When this pod is run, the output of the cat command will be: 

    very

  • You can also control the paths within the volume where ConfigMap keys are projected: 

    apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  containers:
    - name: test-container
      image: gcr.io/google_containers/busybox
      command: [ "/bin/sh", "cat", "/etc/config/path/to/special-key" ]
      volumeMounts:
      - name: config-volume
        mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
        name: special-config
        items:
        - key: special.how
          path: path/to/special-key 1
  restartPolicy: Never
    1
    Path to ConfigMap key.

    When this pod is run, the output of the cat command will be: 

    very