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
ConfigMap with one environment variable
apiVersion: v1 kind: ConfigMap metadata: name: env-config 1 namespace: default data: log_level: INFO 2
Procedure
You can consume the keys of this
ConfigMapin a pod usingconfigMapKeyRefsections.Sample
Podspecification configured to inject specific environment variablesapiVersion: 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
ConfigMapto 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
ConfigMapand keys do not exist. - 8
- Stanza to pull all environment variables from a
ConfigMap. - 9
- Name of the
ConfigMapto 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
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
Podspecification configured to inject specific environment variablesapiVersion: 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
ConfigMapkeys 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
ConfigMapkey.
When this pod is run, the output of the cat command will be:
very
