k8s之Dowanward API详细理解及使用

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

 

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