downwardAPI

downwardAPI

把pod和containers 的信息挂载到容器中

通过变量传递

fieldRef

	可用字段	注释
node级别	spec.nodeName
	status.hostIP
pod级别	metadata.namespace
	metadata.name
	status.podIP
	spec.serviceAccountName
	metadata.uid
	metadata.labels['app']	获取app标签的值
	metadata.annotations['deployment.kubernetes.io/revision']

样例：

# pod.spec.containers.env.valueFrom
  env:
    - name: MY_NODE_NAME
      valueFrom:
        fieldRef:
          fieldPath: spec.nodeName

resourceFieldRef

    - name: MY_POD_cpu_limit
      valueFrom:
        resourceFieldRef:
          resource: limits.cpu
          divisor: 1m  #作为被除数，决定了显示的单位
    - name: MY_POD_cpu_request
      valueFrom:
        resourceFieldRef:
          resource: requests.cpu
          divisor: 1m   #作为被除数，决定了显示的单位
    - name: MY_POD_mem_request
      valueFrom:
        resourceFieldRef:
          resource: requests.memory
          divisor: 1Mi   #作为被除数，决定了显示的单位
    - name: MY_POD_mem_limits
      valueFrom:
        resourceFieldRef:
          resource: limits.memory
          divisor: 1Mi    #作为被除数，决定了显示的单位

通过卷挂载

# pod.spec.volumes.downwardAPI
 
valuems:
- name: pod_info
  downwardAPI:
    items:
      fieldRef:
        fieldPath: spec.nodeName
      resourceFieldRef:
        resource: limits.cpu

containerName: cpu_limit 功能是什么意思

      volumes:
      - downwardAPI:
          defaultMode: 420
          items:
          - path: pod_name
            fieldRef:
              fieldPath: metadata.name
            
          - path: pod_cpu_limit
            resourceFieldRef:
              containerName: cpu_limit
              divisor: "0"
              resource: requests.cpu
        name: podinfo

Information available via resourceFieldRef:

A Container's hugepages limit (providing that the DownwardAPIHugePages feature gate is enabled)
A Container's hugepages request (providing that the DownwardAPIHugePages feature gate is enabled)
A Container's ephemeral-storage limit
A Container's ephemeral-storage request

这些属性只能在env 中引用
status.podIP - the pod's IP address
spec.serviceAccountName - the pod's service account name, available since v1.4.0-alpha.3
spec.nodeName - the node's name, available since v1.4.0-alpha.3
status.hostIP - the node's IP, available since v1.7.0-alpha.1

使用场景

较为典型的是在Pod中运⾏Java应⽤程序时，若未使⽤“-Xmx”选项指
定JVM的堆内存可⽤总量，它默认会设置为主机内存总量的⼀个空间⽐例
（如30%），这会导致容器中的应⽤程序申请内存资源时将会达到上限⽽
转为OOMKilled。另外，即便使⽤了“-Xmx”选项设置其堆内存上限，但它
对于⾮堆内存的可⽤空间不会产⽣任何限制作⽤，结果是仍然存在达到容
器内存资源上限的可能性。
另⼀个颇具代表性的场景是于Pod中运⾏的nginx应⽤，在配置参数
worker_processes的值为“auto”时