Kubernetes Using Container fields as values for environment variables

Use Container fields as values for environment variables

In this exercise, you use Container fields as the values for environment variables. Here is the configuration file for a Pod that has one container:

pradeep@learnk8s$ cat resourcefieldref-demo.yaml
apiVersion: v1
kind: Pod
metadata:
  name: resourcefieldref-demo
spec:
  containers:
    - name: resourcefieldref-demo
      image: k8s.gcr.io/busybox:1.24
      command: [ "sh", "-c"]
      args:
      - while true; do
          echo -en '\n';
          printenv MY_CPU_REQUEST MY_CPU_LIMIT;
          printenv MY_MEM_REQUEST MY_MEM_LIMIT;
          sleep 10;
        done;
      resources:
        requests:
          memory: "32Mi"
          cpu: "125m"
        limits:
          memory: "64Mi"
          cpu: "250m"
      env:
        - name: MY_CPU_REQUEST
          valueFrom:
            resourceFieldRef:
              containerName: resourcefieldref-demo
              resource: requests.cpu
        - name: MY_CPU_LIMIT
          valueFrom:
            resourceFieldRef:
              containerName: resourcefieldref-demo
              resource: limits.cpu
        - name: MY_MEM_REQUEST
          valueFrom:
            resourceFieldRef:
              containerName: resourcefieldref-demo
              resource: requests.memory
        - name: MY_MEM_LIMIT
          valueFrom:
            resourceFieldRef:
              containerName: resourcefieldref-demo
              resource: limits.memory
  restartPolicy: Never

pradeep@learnk8s$ kubectl create -f resourcefieldref-demo.yaml
pod/resourcefieldref-demo created

pradeep@learnk8s$ kubectl get pods -o wide
NAME                    READY   STATUS    RESTARTS   AGE   IP               NODE           NOMINATED NODE   READINESS GATES
fieldref-demo           1/1     Running   0          11m   10.244.205.195   minikube-m02   <none>           <none>
resourcefieldref-demo   1/1     Running   0          65s   10.244.205.196   minikube-m02   <none>           <none>

pradeep@learnk8s$ kubectl logs resourcefieldref-demo

1
1
33554432
67108864

1
1
33554432
67108864

1
1
33554432
67108864

1
1
33554432
67108864

1
1
33554432
67108864

1
1
33554432
67108864

1
1
33554432
67108864

1
1
33554432
67108864

pradeep@learnk8s$ kubectl describe pods resourcefieldref-demo
Name:         resourcefieldref-demo
Namespace:    default
Priority:     0
Node:         minikube-m02/192.168.177.32
Start Time:   Mon, 04 Apr 2022 22:14:44 +0530
Labels:       <none>
Annotations:  cni.projectcalico.org/containerID: bb3594009ddd4bcac025336e96167c14f49b273a6ceaf4106fb5b22d574a04a9
              cni.projectcalico.org/podIP: 10.244.205.196/32
              cni.projectcalico.org/podIPs: 10.244.205.196/32
Status:       Running
IP:           10.244.205.196
IPs:
  IP:  10.244.205.196
Containers:
  resourcefieldref-demo:
    Container ID:  docker://7de83ba72972e4bb7d9d769d80e0f2171d1e65e90ecd289f886acdd599ec9f05
    Image:         k8s.gcr.io/busybox:1.24
    Image ID:      docker-pullable://k8s.gcr.io/busybox@sha256:4bdd623e848417d96127e16037743f0cd8b528c026e9175e22a84f639eca58ff
    Port:          <none>
    Host Port:     <none>
    Command:
      sh
      -c
    Args:
      while true; do echo -en '\n'; printenv MY_CPU_REQUEST MY_CPU_LIMIT; printenv MY_MEM_REQUEST MY_MEM_LIMIT; sleep 10; done;
    State:          Running
      Started:      Mon, 04 Apr 2022 22:15:06 +0530
    Ready:          True
    Restart Count:  0
    Limits:
      cpu:     250m
      memory:  64Mi
    Requests:
      cpu:     125m
      memory:  32Mi
    Environment:
      MY_CPU_REQUEST:  1 (requests.cpu)
      MY_CPU_LIMIT:    1 (limits.cpu)
      MY_MEM_REQUEST:  33554432 (requests.memory)
      MY_MEM_LIMIT:    67108864 (limits.memory)
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-kqs2m (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  kube-api-access-kqs2m:
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   Burstable
Node-Selectors:              <none>
Tolerations:                 node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                             node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  2m7s  default-scheduler  Successfully assigned default/resourcefieldref-demo to minikube-m02
  Normal  Pulling    2m5s  kubelet            Pulling image "k8s.gcr.io/busybox:1.24"
  Normal  Pulled     106s  kubelet            Successfully pulled image "k8s.gcr.io/busybox:1.24" in 18.709565279s
  Normal  Created    106s  kubelet            Created container resourcefieldref-demo
  Normal  Started    106s  kubelet            Started container resourcefieldref-demo