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Creating and using config maps

Understanding config maps

Many applications require configuration by using some combination of configuration files, command line arguments, and environment variables. In OpenShift Container Platform, these configuration artifacts are decoupled from image content to keep containerized applications portable.

The ConfigMap object provides mechanisms to inject containers with configuration data while keeping containers agnostic of OpenShift Container Platform. A config map can be used to store fine-grained information like individual properties or coarse-grained information like entire configuration files or JSON blobs.

The ConfigMap object holds key-value pairs of configuration data that can be consumed in pods or used to store configuration data for system components such as controllers. For example:

ConfigMap Object Definition
kind: ConfigMap
apiVersion: v1
metadata:
  creationTimestamp: 2016-02-18T19:14:38Z
  name: example-config
  namespace: my-namespace
data: (1)
  example.property.1: hello
  example.property.2: world
  example.property.file: |-
    property.1=value-1
    property.2=value-2
    property.3=value-3
binaryData:
  bar: L3Jvb3QvMTAw (2)
1 Contains the configuration data.
2 Points to a file that contains non-UTF8 data, for example, a binary Java keystore file. Enter the file data in Base 64.

You can use the binaryData field when you create a config map from a binary file, such as an image.

Configuration data can be consumed in pods in a variety of ways. A config map can be used to:

  • Populate environment variable values in containers

  • Set command-line arguments in a container

  • Populate configuration files in a volume

Users and system components can store configuration data in a config map.

A config map is similar to a secret, but designed to more conveniently support working with strings that do not contain sensitive information.

Config map restrictions

A config map must be created before its contents can be consumed in pods.

Controllers can be written to tolerate missing configuration data. Consult individual components configured by using config maps on a case-by-case basis.

ConfigMap objects reside in a project.

They can only be referenced by pods in the same project.

The Kubelet only supports the use of a config map for pods it gets from the API server.

This includes any pods created by using the CLI, or indirectly from a replication controller. It does not include pods created by using the OpenShift Container Platform node’s --manifest-url flag, its --config flag, or its REST API because these are not common ways to create pods.

Creating a config map in the OpenShift Container Platform web console

You can create a config map in the OpenShift Container Platform web console.

Procedure

  • To create a config map as a cluster administrator:

    1. In the Administrator perspective, select Workloads → Config Maps.

    2. At the top right side of the page, select Create Config Map.

    3. Enter the contents of your config map.

    4. Select Create.

  • To create a config map as a developer:

    1. In the Developer perspective, select Config Maps.

    2. At the top right side of the page, select Create Config Map.

    3. Enter the contents of your config map.

    4. Select Create.

Creating a config map by using the CLI

You can use the following command to create a config map from directories, specific files, or literal values.

Procedure

  • Create a config map:

    $ oc create configmap <configmap_name> [options]

Creating a config map from a directory

You can create a config map from a directory by using the --from-file flag. This method allows you to use multiple files within a directory to create a config map.

Each file in the directory is used to populate a key in the config map, where the name of the key is the file name, and the value of the key is the content of the file.

For example, the following command creates a config map with the contents of the example-files directory:

$ oc create configmap game-config --from-file=example-files/

View the keys in the config map:

$ oc describe configmaps game-config
Example output
Name:           game-config
Namespace:      default
Labels:         <none>
Annotations:    <none>

Data

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

You can see that the two keys in the map are created from the file names in the directory specified in the command. The content of those keys might be large, so the output of oc describe only shows the names of the keys and their sizes.

Prerequisite

  • You must have a directory with files that contain the data you want to populate a config map with.

    The following procedure uses these example files: game.properties and ui.properties:

    $ cat example-files/game.properties
    Example output
    enemies=aliens
lives=3
enemies.cheat=true
enemies.cheat.level=noGoodRotten
secret.code.passphrase=UUDDLRLRBABAS
secret.code.allowed=true
secret.code.lives=30
    $ cat example-files/ui.properties
    Example output
    color.good=purple
color.bad=yellow
allow.textmode=true
how.nice.to.look=fairlyNice
Procedure

  • Create a config map holding the content of each file in this directory by entering the following command:

    $ oc create configmap game-config \
    --from-file=example-files/
Verification

  • Enter the oc get command for the object with the -o option to see the values of the keys:

    $ oc get configmaps game-config -o yaml
    Example output
    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: 2016-02-18T18:34:05Z
  name: game-config
  namespace: default
  resourceVersion: "407"
  selflink: /api/v1/namespaces/default/configmaps/game-config
  uid: 30944725-d66e-11e5-8cd0-68f728db1985

Creating a config map from a file

You can create a config map from a file by using the --from-file flag. You can pass the --from-file option multiple times to the CLI.

You can also specify the key to set in a config map for content imported from a file by passing a key=value expression to the --from-file option. For example:

$ oc create configmap game-config-3 --from-file=game-special-key=example-files/game.properties

If you create a config map from a file, you can include files containing non-UTF8 data that are placed in this field without corrupting the non-UTF8 data. OpenShift Container Platform detects binary files and transparently encodes the file as MIME. On the server, the MIME payload is decoded and stored without corrupting the data.
Prerequisite

  • You must have a directory with files that contain the data you want to populate a config map with.

    The following procedure uses these example files: game.properties and ui.properties:

    $ cat example-files/game.properties
    Example output
    enemies=aliens
lives=3
enemies.cheat=true
enemies.cheat.level=noGoodRotten
secret.code.passphrase=UUDDLRLRBABAS
secret.code.allowed=true
secret.code.lives=30
    $ cat example-files/ui.properties
    Example output
    color.good=purple
color.bad=yellow
allow.textmode=true
how.nice.to.look=fairlyNice
Procedure

  • Create a config map by specifying a specific file:

    $ oc create configmap game-config-2 \
    --from-file=example-files/game.properties \
    --from-file=example-files/ui.properties

  • Create a config map by specifying a key-value pair:

    $ oc create configmap game-config-3 \
    --from-file=game-special-key=example-files/game.properties
Verification

  • Enter the oc get command for the object with the -o option to see the values of the keys from the file:

    $ oc get configmaps game-config-2 -o yaml
    Example output
    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-2
  namespace: default
  resourceVersion: "516"
  selflink: /api/v1/namespaces/default/configmaps/game-config-2
  uid: b4952dc3-d670-11e5-8cd0-68f728db1985

  • Enter the oc get command for the object with the -o option to see the values of the keys from the key-value pair:

    $ oc get configmaps game-config-3 -o yaml
    Example output
    apiVersion: v1
data:
  game-special-key: |- (1)
    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
    1 This is the key that you set in the preceding step.

Creating a config map from literal values

You can supply literal values for a config map.

The --from-literal option takes a key=value syntax, which allows literal values to be supplied directly on the command line.

Procedure

  • Create a config map by specifying a literal value:

    $ oc create configmap special-config \
    --from-literal=special.how=very \
    --from-literal=special.type=charm
Verification

  • Enter the oc get command for the object with the -o option to see the values of the keys:

    $ oc get configmaps special-config -o yaml
    Example output
    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

Use cases: Consuming config maps in pods

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

Populating environment variables in containers by using config maps

You can use config maps 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 (3)
1 Name of the config map.
2 The project in which the config map resides. Config maps can only be referenced by pods in the same project.
3 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 config map.
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:
  securityContext:
    runAsNonRoot: true
    seccompProfile:
      type: RuntimeDefault
  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 (3)
              key: special.type (4)
              optional: true (5)
      envFrom: (6)
        - configMapRef:
            name: env-config (7)
      securityContext:
        allowPrivilegeEscalation: false
        capabilities:
          drop: [ALL]
  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 Name of the ConfigMap to pull specific environment variables from.
    4 Environment variable to pull from the ConfigMap.
    5 Makes the environment variable optional. As optional, the pod will be started even if the specified ConfigMap and keys do not exist.
    6 Stanza to pull all environment variables from a ConfigMap.
    7 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

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

Setting command-line arguments for container commands with config maps

You can use a config map to set the value of the commands or arguments in a container by using the Kubernetes substitution syntax $(VAR_NAME).

As an example, consider the following config map:

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. 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:
  securityContext:
    runAsNonRoot: true
    seccompProfile:
      type: RuntimeDefault
  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
      securityContext:
        allowPrivilegeEscalation: false
        capabilities:
          drop: [ALL]
  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

Injecting content into a volume by using config maps

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

Example ConfigMap custom resource (CR)
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:
  securityContext:
    runAsNonRoot: true
    seccompProfile:
      type: RuntimeDefault
  containers:
    - name: test-container
      image: gcr.io/google_containers/busybox
      command: [ "/bin/sh", "-c", "cat", "/etc/config/special.how" ]
      volumeMounts:
      - name: config-volume
        mountPath: /etc/config
      securityContext:
        allowPrivilegeEscalation: false
        capabilities:
          drop: [ALL]
  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 config map keys are projected:

    apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  securityContext:
    runAsNonRoot: true
    seccompProfile:
      type: RuntimeDefault
  containers:
    - name: test-container
      image: gcr.io/google_containers/busybox
      command: [ "/bin/sh", "-c", "cat", "/etc/config/path/to/special-key" ]
      volumeMounts:
      - name: config-volume
        mountPath: /etc/config
      securityContext:
        allowPrivilegeEscalation: false
        capabilities:
          drop: [ALL]
  volumes:
    - name: config-volume
      configMap:
        name: special-config
        items:
        - key: special.how
          path: path/to/special-key (1)
  restartPolicy: Never
    1 Path to config map key.

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

    very