nodes-containers-downward-api-container-resources-plugin.adoc

Consuming container resources using a volume plug-in

When creating pods, you can use the downward API to inject information about computing resource requests and limits using a volume plug-in.

Procedure

To use the Volume Plug-in:

1. When creating a pod configuration, use the spec.volumes.downwardAPI.items field to describe the desired resources that correspond to the spec.resources field:

   ....
   spec:
     containers:
       - name: client-container
         image: gcr.io/google_containers/busybox:1.24
         command: ["sh", "-c", "while true; do echo; if [[ -e /etc/cpu_limit ]]; then cat /etc/cpu_limit; fi; if [[ -e /etc/cpu_request ]]; then cat /etc/cpu_request; fi; if [[ -e /etc/mem_limit ]]; then cat /etc/mem_limit; fi; if [[ -e /etc/mem_request ]]; then cat /etc/mem_request; fi; sleep 5; done"]
         resources:
           requests:
             memory: "32Mi"
             cpu: "125m"
           limits:
             memory: "64Mi"
             cpu: "250m"
         volumeMounts:
           - name: podinfo
             mountPath: /etc
             readOnly: false
     volumes:
       - name: podinfo
         downwardAPI:
           items:
             - path: "cpu_limit"
               resourceFieldRef:
                 containerName: client-container
                 resource: limits.cpu
             - path: "cpu_request"
               resourceFieldRef:
                 containerName: client-container
                 resource: requests.cpu
             - path: "mem_limit"
               resourceFieldRef:
                 containerName: client-container
                 resource: limits.memory
             - path: "mem_request"
               resourceFieldRef:
                 containerName: client-container
                 resource: requests.memory
   ....

   If the resource limits are not included in the container configuration, the downward API defaults to the node’s CPU and memory allocatable values.

2. Create the pod from the volume-pod.yaml file:

   $ oc create -f volume-pod.yaml