k8s之Dowanward API详细理解及使用

青旅半醒 2022-12-17 07:26 89阅读 0赞

### Downward API介绍 ###

作用:让Pod里的容器能够直接获取到这个Pod API对象本身的信息

Downward API可以通过以下两种方式将Pod信息注入容器内部

1.环境变量：用于单个变量，可以将Pod信息和Container信息注入到容器内部

2. Volume挂载：通过文件挂载到容器内部

**Downward API支持的常用字段**

1. 使用fieldRef可以声明使用:

spec.nodeName - 宿主机名字

status.hostIP - 宿主机IP

metadata.name - Pod的名字

metadata.namespace - Pod的Namespace

status.podIP - Pod的IP

spec.serviceAccountName - Pod的Service Account的名字

metadata.uid - Pod的UID

metadata.labels\['<KEY>'\] - 指定<KEY>的Label值

metadata.annotations\['<KEY>'\] - 指定<KEY>的Annotation值

metadata.labels - Pod的所有Label

metadata.annotations - Pod的所有Annotation

2. 使用resourceFieldRef可以声明使用:

limits.cpu-容器的CPU limit

requests.cpu-容器的CPU request

limits.memory-容器的memory limit

requests.memory容器的memory request

### Downward API使用 ###

**1.环境变量方式——将pod和容器信息注入为环境变量**

# test-downwardapi-vars.yaml
    apiVersion: v1
    kind: Pod
    metadata:
     name: test-downwardapi-vars
    spec:
     containers:
     - name: test-container
       image: busybox
       imagePullPolicy: IfNotPresent
       command: [ "sh" , "-c" ]
       args:
       - while true; do
          echo -en '\n';
          printenv MY_POD_NAME
          printenv MY_POD_IP
          printenv MY_CPU_REQUEST MY_CPU_LIMIT;
          printenv MY_MEM_REQUEST MY_MEM_LIMIT;
          sleep 3600;
        done;
       resources:
        requests:
         memory: "32Mi"
         cpu: "125m"
        limits:
         memory: "64Mi"
         cpu: "250m"
       env:
       - name: MY_CPU_REQUEST
         valueFrom:
           resourceFieldRef:
            containerName: test-container
            resource: requests.cpu
       - name: MY_CPU_LIMIT
         valueFrom:
           resourceFieldRef:
            containerName: test-container
            resource: limits.cpu
       - name: MY_MEM_REQUEST
         valueFrom:
           resourceFieldRef:
            containerName: test-container
            resource: requests.memory
       - name: MY_MEM_LIMIT
         valueFrom:
           resourceFieldRef:
            containerName: test-container
            resource: limits.memory
       - name: MY_POD_NAME
         valueFrom:
            fieldRef:
              fieldPath: metadata.name
       - name: MY_POD_IP
         valueFrom:
           fieldRef:
             fieldPath: status.podIP
     restartPolicy: Never

\#创建pod

$ kubectl create -f test-downwardapi-vars.yaml

\#查看容器的日志输出（即注入的环境变量）

$ kubectl logs test-downwardapi-vars

![2020102219493341.png][]

**2.Volume挂载方式**

# test-downwardapi-volume.yaml
    apiVersion: v1
    kind: Pod
    metadata:
      name: test-downwardapi-volume
      labels:
        zone: us-est-coast
        cluster: test-cluster1
        rack: rack-22
    spec:
      containers:
        - name: client-container
          image: busybox
          imagePullPolicy: IfNotPresent
          command: ["sh", "-c"]
          args:
          - while true; do
              if [[ -e /etc/podinfo/labels ]]; then
                echo -en '\n\n'; cat /etc/podinfo/labels; fi;
              sleep 500;
            done;
          volumeMounts:
            - name: podinfo
              mountPath: /etc/podinfo
              readOnly: false
      volumes:
        - name: podinfo
          projected:
            sources:
            - downwardAPI:
                items:
                  - path: "labels"
                    fieldRef:
                      fieldPath: metadata.labels

\#创建pod

kubectl create -f test-downwardapi-volume.yaml

\#查看日志输出

kubectl logs test-downwardapi-volume

![20201022195035194.png][]

[2020102219493341.png]: /images/20221123/3a1d9cbce354407ab4e741401e1f24e7.png
[20201022195035194.png]: /images/20221123/36cfdb9ce6a54939828f2a1f124e9625.png