甚麼是Kubernetes ConfigMap

ConfigMap主要功用是儲存我們服務的設定，這使得我們可以將我們的應用服務具備可移植性，當需要相對應的環境參數時，只需要修改ConfigMap，而不需要去更動到image即可更換成新的部屬環境。

為甚麼需要ConfigMap

最主要的用意是共享相同設定。在初期開發時可能只有幾個服務而直接把設定檔寫死，如果在後期變成微服務的架構下，上百個服務都有自己的設定檔在日後維護下會顯得麻煩，因此有了ConfigMap的出現，幫助我們將環境變數與容器鏡像解藕，便於修改應用設定，減少維護成本

何時使用ConfigMap，ConfigMap使用場景

ConfigMap通常儲存服務的環境變數、命令行參數、配置文件等非機密資料，使用場景有設定檔與容器鏡像分離、多環境支持、共享設定、動態設定更新等等

ConfigMap有哪些特點

  • 解藕配置 -> 將服務的設定檔與容器鏡像分離，使服務在不重新建置新的容器鏡像可修改和管理設定檔，提高容器鏡像的通用性和靈活性
  • 靈活性 -> ConfigMap支援多種格式，並且需要時可動態更新設定，無須重啟服務或重新佈署容器
  • 共享設定 -> ConfigMap允許多個Pod共享同一份設定檔，確保了使用相同設定檔的Pod的一致性，提高設定的可維護性和一致性
  • 集中管理 -> ConfigMap在K8s集群中可以集中管理所有的ConfigMap，不需要逐個修改Pod的設定

如何撰寫使用ConfigMap

創建ConfigMap

Imperative(命令式)

  • --from-literal
kubectl create configMap myconfig --from-literal=k1=v1 --from-literal=k2=v2
  • --from-file
kubectl create configMap myconfigfromkey --from-file=fromfilekey=from-key

Declarative(聲明式)

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

使用ConfigMap

使用ConfigMap定義容器環境變量

從單一ConfigMap定義容器環境變量

  • ConfigMap
## create configmap
kubectl create configmap special-config --from-literal=special.how=very
  • Pod
apiVersion: v1
   kind: Pod
   metadata:
     name: dapi-test-pod
   spec:
     containers:
       - name: test-container
         image: registry.k8s.io/busybox
         command: [ "/bin/sh", "-c", "env" ]
         env:
           # 定義環境變量
           - name: SPECIAL_LEVEL_KEY
             valueFrom:
               ConfigMapKeyRef:
                 # ConfigMap 含有你想要指派給 SPECIAL_LEVEL_KEY 的值
                 name: special-config
                 # 指定想要指派的 value 的 key
                 key: special.how
     restartPolicy: Never

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

## Please use the following command to check the output
kubectl logs dapi-test-pod

## output
KUBERNETES_SERVICE_PORT=443
KUBERNETES_PORT=tcp://10.96.0.1:443
HOSTNAME=dapi-test-pod
SHLVL=1
HOME=/root
KUBERNETES_PORT_443_TCP_ADDR=10.96.0.1
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT_443_TCP_PROTO=tcp
SPECIAL_LEVEL_KEY=very
KUBERNETES_PORT_443_TCP=tcp://10.96.0.1:443
KUBERNETES_SERVICE_PORT_HTTPS=443
PWD=/
KUBERNETES_SERVICE_HOST=10.96.0.1

從上述輸出可以看到環境變量有SPECIAL_LEVEL_KEY=very

從多個ConfigMap定義容器環境變量

  • ConfigMap
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 configmap
kubectl create -f https://kubernetes.io/examples/ConfigMap/configmap.yaml
  • Pod
apiVersion: v1
  kind: Pod
  metadata:
    name: dapi-test-pod
  spec:
    containers:
      - name: test-container
        image: registry.k8s.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 pod
kubectl create -f https://kubernetes.io/examples/pods/pod-multiple-configmap-env-variable.yaml

## Please use the following command to check the output
kubectl logs dapi-test-pod

## output
KUBERNETES_PORT=tcp://10.96.0.1:443
KUBERNETES_SERVICE_PORT=443
LOG_LEVEL=INFO
HOSTNAME=dapi-test-pod
SHLVL=1
HOME=/root
KUBERNETES_PORT_443_TCP_ADDR=10.96.0.1
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT_443_TCP_PROTO=tcp
SPECIAL_LEVEL_KEY=very
KUBERNETES_PORT_443_TCP=tcp://10.96.0.1:443
KUBERNETES_SERVICE_PORT_HTTPS=443
PWD=/
KUBERNETES_SERVICE_HOST=10.96.0.1

從上述輸出可以看到環境變量有LOG_LEVEL=INFO和SPECIAL_LEVEL_KEY=very

在ConfigMap設定key-value pairs定義容器環境變量

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

## create configmap
kubectl create -f https://kubernetes.io/examples/configmap/configmap-multikeys.yaml
  • Pod
apiVersion: v1
  kind: Pod
  metadata:
    name: dapi-test-pod
  spec:
    containers:
      - name: test-container
        image: registry.k8s.io/busybox
        command: [ "/bin/sh", "-c", "env" ]
        envFrom:
        - ConfigMapRef:
            name: special-config
   restartPolicy: Never

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

我們使用了 envFrom 來將 ConfigMap 中的所有 data 都定義成容器環境變量。

## Please use the following command to check the output
kubectl logs dapi-test-pod

## output
KUBERNETES_PORT=tcp://10.96.0.1:443
KUBERNETES_SERVICE_PORT=443
HOSTNAME=dapi-test-pod
SHLVL=1
HOME=/root
SPECIAL_LEVEL=very
KUBERNETES_PORT_443_TCP_ADDR=10.96.0.1
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT_443_TCP_PROTO=tcp
KUBERNETES_PORT_443_TCP=tcp://10.96.0.1:443
KUBERNETES_SERVICE_PORT_HTTPS=443
PWD=/
KUBERNETES_SERVICE_HOST=10.96.0.1
SPECIAL_TYPE=charm

從上述輸出可以看到環境變量有SPECIAL_LEVEL=very和SPECIAL_TYPE=charm。

在Pod commands使用ConfigMap定義的環境變量

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

## create configmap
kubectl create -f https://kubernetes.io/examples/configmap/configmap-multikeys.yaml
  • Pod
apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  containers:
    - name: test-container
      image: registry.k8s.io/busybox
      command: [ "/bin/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

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

我們可以使用ConfigMap定義好的環境變量在容器的command和args，使用語法為$(VAR_NAME)

## Please use the following command to check the output
kubectl logs dapi-test-pod

## output
very charm

將 ConfigMap 資料加到 Volume

當我們建立ConfigMap使用--from-file，檔名會變成data區塊的key，而內容則會變成該key的value

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

## create configmap
kubectl create -f https://kubernetes.io/examples/configmap/configmap-multikeys.yaml
  • Pod
apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  containers:
    - name: test-container
      image: registry.k8s.io/busybox
      command: [ "/bin/sh", "-c", "ls /etc/config/" ]
      volumeMounts:
      - name: config-volume
        mountPath: /etc/config
  volumes:
    - name: config-volume
      ConfigMap:
        # 提供container要使用的configmap name
        name: special-config
  restartPolicy: Never


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

將ConfigMap name 添加到volumes區塊進行掛載，在此範例中，mountPath會是/etc/config

## Please use the following command to check the output
kubectl logs dapi-test-pod

## output
SPECIAL_LEVEL
SPECIAL_TYPE

此Pod會去執行ls /etc/config，如果該目錄下有其他檔案會被刪除，因為使用的掛載方式是mountPath

將ConfigMap資料加到Volume特定路徑

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

## create configmap
kubectl create -f https://kubernetes.io/examples/configmap/configmap-multikeys.yaml
  • Pod
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 pod
kubectl create -f https://kubernetes.io/examples/pods/pod-configmap-volume-specific-key.yaml

使用 path 欄位來指定特定 ConfigMap item 到想要的檔案路徑。 在此範例中, SPECIAL_LEVEL item 將會被掛載到 config-volume volume 中的 /etc/config/keys

## Please use the following command to check the output
kubectl logs dapi-test-pod

## output
very

Reference