6.2. Estimating the number of pods your OpenShift Container Platform nodes can hold

Run the following command:

$ ./cluster-capacity --kubeconfig <path-to-kubeconfig> \ 1
    --podspec <path-to-pod-spec> 2

You can also add the --verbose option to output a detailed description of how many pods can be scheduled on each node in the cluster:

$ ./cluster-capacity --kubeconfig <path-to-kubeconfig> \
    --podspec <path-to-pod-spec> --verbose

small-pod pod requirements:
	- CPU: 150m
	- Memory: 100Mi

The cluster can schedule 52 instance(s) of the pod small-pod.

Termination reason: Unschedulable: No nodes are available that match all of the
following predicates:: Insufficient cpu (2).

Pod distribution among nodes:
small-pod
	- 192.168.124.214: 26 instance(s)
	- 192.168.124.120: 26 instance(s)

In the above example, the number of estimated pods that can be scheduled onto the cluster is 52.

Create the cluster role:

$ cat << EOF| oc create -f -

kind: ClusterRole
apiVersion: v1
metadata:
  name: cluster-capacity-role
rules:
- apiGroups: [""]
  resources: ["pods", "nodes", "persistentvolumeclaims", "persistentvolumes", "services"]
  verbs: ["get", "watch", "list"]
EOF

Create the service account:

$ oc create sa cluster-capacity-sa

Add the role to the service account:

$ oc adm policy add-cluster-role-to-user cluster-capacity-role \
    system:serviceaccount:default:cluster-capacity-sa

Define and create the Pod spec:

apiVersion: v1
kind: Pod
metadata:
  name: small-pod
  labels:
    app: guestbook
    tier: frontend
spec:
  containers:
  - name: php-redis
    image: gcr.io/google-samples/gb-frontend:v4
    imagePullPolicy: Always
    resources:
      limits:
        cpu: 150m
        memory: 100Mi
      requests:
        cpu: 150m
        memory: 100Mi

The cluster capacity analysis is mounted in a volume using a ConfigMap object named cluster-capacity-configmap to mount input pod spec file pod.yaml into a volume test-volume at the path /test-pod.

If you haven’t created a ConfigMap object, create one before creating the job:

$ oc create configmap cluster-capacity-configmap \
    --from-file=pod.yaml=pod.yaml

Create the job using the below example of a job specification file:

apiVersion: batch/v1
kind: Job
metadata:
  name: cluster-capacity-job
spec:
  parallelism: 1
  completions: 1
  template:
    metadata:
      name: cluster-capacity-pod
    spec:
        containers:
        - name: cluster-capacity
          image: openshift/origin-cluster-capacity
          imagePullPolicy: "Always"
          volumeMounts:
          - mountPath: /test-pod
            name: test-volume
          env:
          - name: CC_INCLUSTER 1
            value: "true"
          command:
          - "/bin/sh"
          - "-ec"
          - |
            /bin/cluster-capacity --podspec=/test-pod/pod.yaml --verbose
        restartPolicy: "Never"
        serviceAccountName: cluster-capacity-sa
        volumes:
        - name: test-volume
          configMap:
            name: cluster-capacity-configmap

Run the cluster capacity image as a job in a pod:

$ oc create -f cluster-capacity-job.yaml

Check the job logs to find the number of pods that can be scheduled in the cluster:

$ oc logs jobs/cluster-capacity-job

small-pod pod requirements:
        - CPU: 150m
        - Memory: 100Mi

The cluster can schedule 52 instance(s) of the pod small-pod.

Termination reason: Unschedulable: No nodes are available that match all of the
following predicates:: Insufficient cpu (2).

Pod distribution among nodes:
small-pod
        - 192.168.124.214: 26 instance(s)
        - 192.168.124.120: 26 instance(s)