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Configure a Pod to Use a ConfigMap

ConfigMaps allow you to decouple configuration artifacts from image content to keep containerized applications portable. This page provides a series of usage examples demonstrating how to create ConfigMaps and configure Pods using data stored in ConfigMaps.

• Before you begin
• Create a ConfigMap
• Define container environment variables using ConfigMap data
• Configure all key-value pairs in a ConfigMap as container environment variables
• Use ConfigMap-defined environment variables in Pod commands
• Add ConfigMap data to a Volume
• Understanding ConfigMaps and Pods
• What's next

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

• Katacoda
• Play with Kubernetes

To check the version, enter kubectl version.

Create a ConfigMap

Use the kubectl create configmap command to create configmaps from directories, files, or literal values:

kubectl create configmap <map-name> <data-source>

where <map-name> is the name you want to assign to the ConfigMap and <data-source> is the directory, file, or literal value to draw the data from.

The data source corresponds to a key-value pair in the ConfigMap, where

• key = the file name or the key you provided on the command line, and
• value = the file contents or the literal value you provided on the command line.

You can use kubectl describe or kubectl get to retrieve information about a ConfigMap.

Create ConfigMaps from directories

You can use kubectl create configmap to create a ConfigMap from multiple files in the same directory.

For example:

# Create the local directory
mkdir -p configure-pod-container/configmap/

# Download the sample files into `configure-pod-container/configmap/` directory
wget https://k8s.io/examples/configmap/game.properties -O configure-pod-container/configmap/game.properties
wget https://k8s.io/examples/configmap/ui.properties -O configure-pod-container/configmap/ui.properties

# Create the configmap
kubectl create configmap game-config --from-file=configure-pod-container/configmap/

combines the contents of the configure-pod-container/configmap/ directory

game.properties
ui.properties

into the following ConfigMap:

kubectl describe configmaps game-config

where the output is similar to this:

Name:           game-config
Namespace:      default
Labels:         <none>
Annotations:    <none>

Data
====
game.properties:        158 bytes
ui.properties:          83 bytes

The game.properties and ui.properties files in the configure-pod-container/configmap/ directory are represented in the data section of the ConfigMap.

kubectl get configmaps game-config -o yaml

The output is similar to this:

apiVersion: v1
data:
  game.properties: |
    enemies=aliens
    lives=3
    enemies.cheat=true
    enemies.cheat.level=noGoodRotten
    secret.code.passphrase=UUDDLRLRBABAS
    secret.code.allowed=true
    secret.code.lives=30
  ui.properties: |
    color.good=purple
    color.bad=yellow
    allow.textmode=true
    how.nice.to.look=fairlyNice
kind: ConfigMap
metadata:
  creationTimestamp: 2016-02-18T18:52:05Z
  name: game-config
  namespace: default
  resourceVersion: "516"
  selfLink: /api/v1/namespaces/default/configmaps/game-config
  uid: b4952dc3-d670-11e5-8cd0-68f728db1985

Create ConfigMaps from files

You can use kubectl create configmap to create a ConfigMap from an individual file, or from multiple files.

For example,

kubectl create configmap game-config-2 --from-file=configure-pod-container/configmap/game.properties

would produce the following ConfigMap:

kubectl describe configmaps game-config-2

where the output is similar to this:

Name:           game-config-2
Namespace:      default
Labels:         <none>
Annotations:    <none>

Data
====
game.properties:        158 bytes

You can pass in the --from-file argument multiple times to create a ConfigMap from multiple data sources.

kubectl create configmap game-config-2 --from-file=configure-pod-container/configmap/game.properties --from-file=configure-pod-container/configmap/ui.properties

Describe the above game-config-2 configmap created

kubectl describe configmaps game-config-2

The output is similar to this:

Name:           game-config-2
Namespace:      default
Labels:         <none>
Annotations:    <none>

Data
====
game.properties:        158 bytes
ui.properties:          83 bytes

Use the option --from-env-file to create a ConfigMap from an env-file, for example:

# Env-files contain a list of environment variables.
# These syntax rules apply:
#   Each line in an env file has to be in VAR=VAL format.
#   Lines beginning with # (i.e. comments) are ignored.
#   Blank lines are ignored.
#   There is no special handling of quotation marks (i.e. they will be part of the ConfigMap value)).

# Download the sample files into `configure-pod-container/configmap/` directory
wget https://k8s.io/examples/configmap/game-env-file.properties -O configure-pod-container/configmap/game-env-file.properties

# The env-file `game-env-file.properties` looks like below
cat configure-pod-container/configmap/game-env-file.properties
enemies=aliens
lives=3
allowed="true"

# This comment and the empty line above it are ignored

kubectl create configmap game-config-env-file \
       --from-env-file=configure-pod-container/configmap/game-env-file.properties

would produce the following ConfigMap:

kubectl get configmap game-config-env-file -o yaml

where the output is similar to this:

apiVersion: v1
data:
  allowed: '"true"'
  enemies: aliens
  lives: "3"
kind: ConfigMap
metadata:
  creationTimestamp: 2017-12-27T18:36:28Z
  name: game-config-env-file
  namespace: default
  resourceVersion: "809965"
  selfLink: /api/v1/namespaces/default/configmaps/game-config-env-file
  uid: d9d1ca5b-eb34-11e7-887b-42010a8002b8

When passing --from-env-file multiple times to create a ConfigMap from multiple data sources, only the last env-file is used:

# Download the sample files into `configure-pod-container/configmap/` directory
wget https://k8s.io/examples/configmap/ui-env-file.properties -O configure-pod-container/configmap/ui-env-file.properties

# Create the configmap
kubectl create configmap config-multi-env-files \
        --from-env-file=configure-pod-container/configmap/game-env-file.properties \
        --from-env-file=configure-pod-container/configmap/ui-env-file.properties

would produce the following ConfigMap:

kubectl get configmap config-multi-env-files -o yaml

where the output is similar to this:

apiVersion: v1
data:
  color: purple
  how: fairlyNice
  textmode: "true"
kind: ConfigMap
metadata:
  creationTimestamp: 2017-12-27T18:38:34Z
  name: config-multi-env-files
  namespace: default
  resourceVersion: "810136"
  selfLink: /api/v1/namespaces/default/configmaps/config-multi-env-files
  uid: 252c4572-eb35-11e7-887b-42010a8002b8

Define the key to use when creating a ConfigMap from a file

You can define a key other than the file name to use in the data section of your ConfigMap when using the --from-file argument:

kubectl create configmap game-config-3 --from-file=<my-key-name>=<path-to-file>

where <my-key-name> is the key you want to use in the ConfigMap and <path-to-file> is the location of the data source file you want the key to represent.

For example:

kubectl create configmap game-config-3 --from-file=game-special-key=configure-pod-container/configmap/game.properties

would produce the following ConfigMap:

kubectl get configmaps game-config-3 -o yaml

where the output is similar to this:

apiVersion: v1
data:
  game-special-key: |
    enemies=aliens
    lives=3
    enemies.cheat=true
    enemies.cheat.level=noGoodRotten
    secret.code.passphrase=UUDDLRLRBABAS
    secret.code.allowed=true
    secret.code.lives=30
kind: ConfigMap
metadata:
  creationTimestamp: 2016-02-18T18:54:22Z
  name: game-config-3
  namespace: default
  resourceVersion: "530"
  selfLink: /api/v1/namespaces/default/configmaps/game-config-3
  uid: 05f8da22-d671-11e5-8cd0-68f728db1985

Create ConfigMaps from literal values

You can use kubectl create configmap with the --from-literal argument to define a literal value from the command line:

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

You can pass in multiple key-value pairs. Each pair provided on the command line is represented as a separate entry in the data section of the ConfigMap.

kubectl get configmaps special-config -o yaml

The output is similar to this:

apiVersion: v1
data:
  special.how: very
  special.type: charm
kind: ConfigMap
metadata:
  creationTimestamp: 2016-02-18T19:14:38Z
  name: special-config
  namespace: default
  resourceVersion: "651"
  selfLink: /api/v1/namespaces/default/configmaps/special-config
  uid: dadce046-d673-11e5-8cd0-68f728db1985

Define container environment variables using ConfigMap data

Define a container 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.

pods/pod-single-configmap-env-variable.yaml

apiVersion: v1 kind: Pod metadata: name: dapi-test-pod spec: containers: - name: test-container image: k8s.gcr.io/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

Create the Pod:

 kubectl create -f https://k8s.io/examples/pods/pod-single-configmap-env-variable.yaml

Now, the Pod’s output includes SPECIAL_LEVEL_KEY=very.

Define container environment variables with data from multiple ConfigMaps

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

configmap/configmaps.yaml
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

Create the ConfigMap:

 kubectl create -f https://k8s.io/examples/configmap/configmaps.yaml

• Define the environment variables in the Pod specification.
  

pods/pod-multiple-configmap-env-variable.yaml
apiVersion: v1 kind: Pod metadata: name: dapi-test-pod spec: containers: - name: test-container image: k8s.gcr.io/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

Create the Pod:

 kubectl create -f https://k8s.io/examples/pods/pod-multiple-configmap-env-variable.yaml

Now, the Pod’s output includes SPECIAL_LEVEL_KEY=very and LOG_LEVEL=INFO.

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

Note: This functionality is available in Kubernetes v1.6 and later.

• Create a ConfigMap containing multiple key-value pairs.
  

configmap/configmap-multikeys.yaml
apiVersion: v1 kind: ConfigMap metadata: name: special-config namespace: default data: SPECIAL_LEVEL: very SPECIAL_TYPE: charm

Create the ConfigMap:

 kubectl create -f https://k8s.io/examples/configmap/configmap-multikeys.yaml

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

pods/pod-configmap-envFrom.yaml
apiVersion: v1 kind: Pod metadata: name: dapi-test-pod spec: containers: - name: test-container image: k8s.gcr.io/busybox command: [ "/bin/sh", "-c", "env" ] envFrom: - configMapRef: name: special-config restartPolicy: Never

Create the Pod:

 kubectl create -f https://k8s.io/examples/pods/pod-configmap-envFrom.yaml

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

pods/pod-configmap-env-var-valueFrom.yaml

apiVersion: v1 kind: Pod metadata: name: dapi-test-pod spec: containers: - name: test-container image: k8s.gcr.io/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

created by running

kubectl create -f https://k8s.io/examples/pods/pod-configmap-env-var-valueFrom.yaml

produces the following output in the test-container container:

very charm

Add ConfigMap data to a Volume

As explained in Create ConfigMaps from files, 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.

configmap/configmap-multikeys.yaml
apiVersion: v1 kind: ConfigMap metadata: name: special-config namespace: default data: SPECIAL_LEVEL: very SPECIAL_TYPE: charm

Create the ConfigMap:

kubectl create -f https://k8s.io/examples/configmap/configmap-multikeys.yaml

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.

pods/pod-configmap-volume.yaml

apiVersion: v1 kind: Pod metadata: name: dapi-test-pod spec: containers: - name: test-container image: k8s.gcr.io/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

Create the Pod:

kubectl create -f https://k8s.io/examples/pods/pod-configmap-volume.yaml

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

special.level
special.type

Caution: If there are some files in the /etc/config/ directory, they will be deleted.

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.

pods/pod-configmap-volume-specific-key.yaml
apiVersion: v1 kind: Pod metadata: name: dapi-test-pod spec: containers: - name: test-container image: k8s.gcr.io/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

Create the Pod:

kubectl create -f https://k8s.io/examples/pods/pod-configmap-volume-specific-key.yaml

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.

Note: A container using a ConfigMap as a subPath volume will not receive ConfigMap updates.

Understanding ConfigMaps and Pods

The ConfigMap API resource stores configuration data as key-value pairs. The data can be consumed in pods or provide the configurations for system components such as controllers. ConfigMap is similar to Secrets, but provides a means of working with strings that don’t contain sensitive information. Users and system components alike can store configuration data in ConfigMap.

Note: ConfigMaps should reference properties files, not replace them. Think of the ConfigMap as representing something similar to the Linux /etc directory and its contents. For example, if you create a Kubernetes Volume from a ConfigMap, each data item in the ConfigMap is represented by an individual file in the volume.

The ConfigMap’s data field contains the configuration data. As shown in the example below, this can be simple – like individual properties defined using --from-literal – or complex – like configuration files or JSON blobs defined using --from-file.

kind: ConfigMap
apiVersion: v1
metadata:
  creationTimestamp: 2016-02-18T19:14:38Z
  name: example-config
  namespace: default
data:
  # example of a simple property defined using --from-literal
  example.property.1: hello
  example.property.2: world
  # example of a complex property defined using --from-file
  example.property.file: |-
    property.1=value-1
    property.2=value-2
    property.3=value-3

Restrictions

• 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.

• 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

The output is similar to this:

   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.

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

• Kubelet doesn’t support the use of ConfigMaps for pods not found on the API server. This includes 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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What's next

• Follow a real world example of Configuring Redis using a ConfigMap.

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