Kubernetes资源对象之ConfigMap

在大规模分布式系统中有一个分布式配置管理中心的组件，将分布式应用所需的配置信息与程序进行分离，极大简化配置管理的工作。如360的QConf，百度的Disconf。在大规模容器集群环境中，容器内应用程序的配置管理十分重要。Kubernetes提供了一种统一的管理方案，即ConfigMap。 Kubernetes使用ConfigMap实现容器应用的配置管理。

创建ConfigMap

下面介绍如何创建ConfigMap:

使用yaml创建ConfigMap

ConfigMap yaml的详细定义参考这里resources-reference ConfigMap v1。

下面是一个简单的例子：captcha-cfg.yaml，其中配置信息即可以是captchaRunMode: dev这种键值对，又可以保存一个完成的配置文件内容如app.properites

apiVersion: v1
kind: ConfigMap
metadata:
  name: captcha-cfg
data:
  captchaRunMode: dev
  imageDir: /home/captcha
  app.properties: |
    property.1=value-1
    property.2=value-2
    property.3=value-3

使用kubectl create创建此ConfigMap:

kubectl create -f captcha-cfg.yaml

查看创建的ConfigMap

kubectl get configmap
NAME               DATA      AGE
captcha-cfg        2         42s


kubectl describe configmap captcha-cfg
Name:           captcha-cfg
Namespace:      default
Labels:         <none>
Annotations:    <none>

Data
====
app.properties: 57 bytes
captchaRunMode: 3 bytes
imageDir:       13 bytes


kubectl get configmap captcha-cfg -o yaml
apiVersion: v1
data:
  app.properties: |
    property.1=value-1
    property.2=value-2
    property.3=value-3
  captchaRunMode: dev
  imageDir: /home/captcha
kind: ConfigMap
metadata:
  creationTimestamp: 2017-02-17T11:53:28Z
  name: captcha-cfg
  namespace: default
  resourceVersion: "71238"
  selfLink: /api/v1/namespaces/default/configmaps/captcha-cfg
  uid: b1eda86a-f507-11e6-98ca-0800279704c8

###直接使用kubectl命令创建

从目录创建

kubectl create configmap game-config --from-file=docs/user-guide/configmap/kubectl

从文件创建

kubectl create configmap game-config-2 --from-file=docs/user-guide/configmap/kubectl/game.properties --from-file=docs/user-guide/configmap/kubectl/ui.properties

从字面值创建

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

使用ConfigMap

环境变量方式

这种方式将作为容器内的环境变量。

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

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: SPECIAL_TYPE_KEY
          valueFrom:
            configMapKeyRef:
              name: special-config
              key: special.type
  restartPolicy: Never
  

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: a-config
              key: akey
              optional: true
  restartPolicy: Never

命令行参数方式

这种方式需要先设置为环境变量，之后可以通过$(VAR_NAME)设置容器启动命令的启动参数。

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

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.how
        - name: SPECIAL_TYPE_KEY
          valueFrom:
            configMapKeyRef:
              name: special-config
              key: special.type
  restartPolicy: Never

volume plugin方式

这种方式将以volume的形式挂载为容器内部的文件或目录。

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

 
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/special.how" ]
      volumeMounts:
      - name: config-volume
        mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
        name: special-config
  restartPolicy: Never


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/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
  restartPolicy: Never
  
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:
        name: no-config
        optional: true
  restartPolicy: Never

使用ConfigMap的一些限制

ConfigMap必须在Pod之前被创建
如果ConfigMap定义了Namespace, 则只有相同的Namespace的Pod才可以使用。
目前ConfigMap的限额管理还未实现。