The number of pod replicas for a specific deployment can be increased or decreased to meet your needs. Despite the ReplicaSet and ReplicationController resources, the number of replicas needed for an application is typically defined in a deployment resource. A replica set or replication controller (managed by a deployment) guarantees that the specified number of replicas of a pod are running at all times. The replica set or replication controller can add or remove pods as necessary to conform to the desired replica count.
Deployment resources contain:
- The desired number of replicas
- A selector for identifying managed pods
- A pod definition, or template, for creating a replicated pod (including labels to apply to the pod)
Create a new project for this guided exercise named schedule-scale.
oc new-project schedule-scale
Deploy a test application for this exercise which explicitly requests container resources for CPU and memory.
oc apply -f 01-deployment.yaml -n schedule-scale
Verify that your application pod has a status of Running. You might need to run the oc get pods command multiple times.
oc get pods
Verify that your application pod specifies resource limits and requests.
oc describe pod/pod | grep -A2 -E "Limits|Requests"
Manually scale the deployment by first increasing and then decreasing the number of running pods.
Scale the deployment up to five pods.
oc scale --replicas 5 deployment/scale
Verify that all five application pods are running. You might need to run the oc get pods command multiple times.
Scale the deployment back down to one pod.
oc scale --replicas 1 deployment/scale
Configure the application to automatically scale based on load, and then test the application by applying load.
Create a horizontal pod autoscaler that ensures the loadtest application always has 2 application pods running; that number can be increased to a maximum of 10 pods when CPU load exceeds 50%.
oc autoscale deployment/scale --min 2 --max 10 --cpu-percent 50
Wait until the loadtest horizontal pod autoscaler reports usage in the TARGETS column.
oc get hpa/scale
watch "oc get po;oc adm top po --use-protocol-buffers;oc get hpa"
oc delete project schedule-scale