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Use ConfigMap Data in Pods

This page provides a series of usage examples demonstrating how to configure Pods using data stored in ConfigMaps.

Before you begin

Define Pod environment variables using ConfigMap data

Define a Pod environment variable with data from a single ConfigMap

  1. Define an environment variable as a key-value pair in a ConfigMap:

    kubectl create configmap special-config --from-literal=special.how=very

  2. Assign the special.how value defined in the ConfigMap to the SPECIAL_LEVEL_KEY environment variable in the Pod specification.

    kubectl edit pod dapi-test-pod

    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:
        # Define the environment variable
        - name: SPECIAL_LEVEL_KEY
          valueFrom:
            configMapKeyRef:
              # The ConfigMap containing the value you want to assign to SPECIAL_LEVEL_KEY
              name: special-config
              # Specify the key associated with the value
              key: special.how
  restartPolicy: Never

  3. Save the changes to the Pod specification. Now, the Pod’s output includes SPECIAL_LEVEL_KEY=very.

Define Pod environment variables with data from multiple ConfigMaps

  1. As with the previous example, create the ConfigMaps first.

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

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

  2. Define the environment variables in the Pod specification.

    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:
        - name: SPECIAL_LEVEL_KEY
          valueFrom:
            configMapKeyRef:
              name: special-config
              key: special.how
        - name: LOG_LEVEL
          valueFrom:
            configMapKeyRef:
              name: env-config
              key: log_level
  restartPolicy: Never

  3. Save the changes to the Pod specification. Now, the Pod’s output includes SPECIAL_LEVEL_KEY=very and LOG_LEVEL=info.

Configure all key-value pairs in a ConfigMap as Pod environment variables

Note: This functionality is available to users running Kubernetes v1.6 and later.

  1. Create a ConfigMap containing multiple key-value pairs.

    apiVersion: v1
kind: ConfigMap
metadata:
  name: special-config
  namespace: default
data:
  SPECIAL_LEVEL: very
  SPECIAL_TYPE: charm

  2. Use envFrom to define all of the ConfigMap’s data as Pod environment variables. The key from the ConfigMap becomes the environment variable name in the Pod.

    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" ]
      envFrom:
      - configMapRef:
          name: special-config
  restartPolicy: Never

  3. Save the changes to the Pod specification. Now, the Pod’s output includes SPECIAL_LEVEL=very and SPECIAL_TYPE=charm.

Use ConfigMap-defined environment variables in Pod commands

You can use ConfigMap-defined environment variables in the command section of the Pod specification using the $(VAR_NAME) Kubernetes substitution syntax.

For example:

The following Pod specification

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)" ]
      env:
        - name: SPECIAL_LEVEL_KEY
          valueFrom:
            configMapKeyRef:
              name: special-config
              key: special_level
        - name: SPECIAL_TYPE_KEY
          valueFrom:
            configMapKeyRef:
              name: special-config
              key: special_type
  restartPolicy: Never

produces the following output in the test-container container:

very charm

Add ConfigMap data to a Volume

As explained in Configure Containers Using a ConfigMap, when you create a ConfigMap using --from-file, the filename becomes a key stored in the data section of the ConfigMap. The file contents become the key’s value.

The examples in this section refer to a ConfigMap named special-config, shown below.

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

Populate a Volume with data stored in a ConfigMap

Add the ConfigMap name under the volumes section of the Pod specification. This adds the ConfigMap data to the directory specified as volumeMounts.mountPath (in this case, /etc/config). The command section references the special.level item stored in the ConfigMap.

apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  containers:
    - name: test-container
      image: gcr.io/google_containers/busybox
      command: [ "/bin/sh", "-c", "ls /etc/config/" ]
      volumeMounts:
      - name: config-volume
        mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
        # Provide the name of the ConfigMap containing the files you want
        # to add to the container
        name: special-config
  restartPolicy: Never

When the pod runs, the command ("ls /etc/config/") produces the output below:

special.level
special.type

Add ConfigMap data to a specific path in the Volume

Use the path field to specify the desired file path for specific ConfigMap items. In this case, the special.level item will be mounted in the config-volume volume at /etc/config/keys.

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

When the pod runs, the command ("cat /etc/config/keys") produces the output below:

very

Project keys to specific paths and file permissions

You can project keys to specific paths and specific permissions on a per-file basis. The Secrets user guide explains the syntax.

Mounted ConfigMaps are updated automatically

When a ConfigMap already being consumed in a volume is updated, projected keys are eventually updated as well. Kubelet is checking whether the mounted ConfigMap is fresh on every periodic sync. However, it is using its local ttl-based cache for getting the current value of the ConfigMap. As a result, the total delay from the moment when the ConfigMap is updated to the moment when new keys are projected to the pod can be as long as kubelet sync period + ttl of ConfigMaps cache in kubelet.

Understanding ConfigMaps and Pods

Restrictions

  1. You must create a ConfigMap before referencing it in a Pod specification (unless you mark the ConfigMap as “optional”). If you reference a ConfigMap that doesn’t exist, the Pod won’t start. Likewise, references to keys that don’t exist in the ConfigMap will prevent the pod from starting.

  2. If you use envFrom to define environment variables from ConfigMaps, keys that are considered invalid will be skipped. The pod will be allowed to start, but the invalid names will be recorded in the event log (InvalidVariableNames). The log message lists each skipped key. For example:

    kubectl get events
LASTSEEN FIRSTSEEN COUNT NAME          KIND  SUBOBJECT  TYPE      REASON                            SOURCE                MESSAGE
0s       0s        1     dapi-test-pod Pod              Warning   InvalidEnvironmentVariableNames   {kubelet, 127.0.0.1}  Keys [1badkey, 2alsobad] from the EnvFrom configMap default/myconfig were skipped since they are considered invalid environment variable names.

  3. ConfigMaps reside in a specific namespace. A ConfigMap can only be referenced by pods residing in the same namespace.

  4. Kubelet doesn’t support the use of ConfigMaps for pods not found on the API server. This includes every pod created using kubectl or indirectly via a replication controller. It does not include pods created via the Kubelet’s --manifest-url flag, --config flag, or the Kubelet REST API.

    Note: These are not commonly-used ways to create pods.

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