Resource Requests

Stackable operators handle resource requests in a sligtly different manner than Kubernetes. Resource requests are defined on role or group level. See Roles and role groups for details on these concepts. On a role level this means that e.g. all workers will use the same resource requests and limits. This can be further specified on role group level (which takes priority to the role level) to apply different resources.

This is an example on how to specify CPU and memory resources using the Stackable Custom Resources:

---
apiVersion: example.stackable.tech/v1alpha1
kind: ExampleCluster
metadata:
  name: example
spec:
  workers: # role-level
    config:
      resources:
        cpu:
          min: 300m
          max: 600m
        memory:
          limit: 3Gi
    roleGroups: # role-group-level
      resources-from-role: # role-group 1
        replicas: 1
      resources-from-role-group: # role-group 2
        replicas: 1
        config:
          resources:
            cpu:
              min: 400m
              max: 800m
            memory:
              limit: 4Gi

In this case, the role group resources-from-role will inherit the resources specified on the role level. Resulting in a maximum of 3Gi memory and 600m CPU resources.

The role group resources-from-role-group has maximum of 4Gi memory and 800m CPU resources (which overrides the role CPU resources).

For Java products the actual used Heap memory is lower than the specified memory limit due to other processes in the Container requiring memory to run as well. Currently, 80% of the specified memory limits is passed to the JVM.

For memory only a limit can be specified, which will be set as memory request and limit in the Container. This is to always guarantee a Container the full amount memory during Kubernetes scheduling.

A minimal HA setup consisting of 2 Hive metastore instances has the following resource requirements:

  • 100m CPU request

  • 3000m CPU limit

  • 1280m memory request and limit

Of course, additional services, require additional resources. For Stackable components, see the corresponding documentation on further resource requirements.

Corresponding to the values above, the operator uses the following resource defaults:

metastore:
  roleGroups:
    default:
      config:
        resources:
          requests:
            cpu: "250m"
            memory: "512Mi"
          limits:
            cpu: "1000m"
            memory: "512Mi"

The operator may configure an additional container for log aggregation. This is done when log aggregation is configured as described in Logging. The resources for this container cannot be configured using the mechanism described above. Use podOverrides for this purpose.

You can configure your own resource requests and limits by following the example above.

For more details regarding Kubernetes CPU limits see: Assign CPU Resources to Containers and Pods.