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 schedulers, 2 workers and 2 webservers has the following resource requirements:

  • 3500m CPU request

  • 8600m CPU limit

  • 10156Mi memory request and limit

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

spec:
  schedulers:
    config:
      resources:
        cpu:
          min: 100m
          max: 400m
        memory:
          limit: 512Mi
  workers:
    config:
      resources:
        cpu:
          min: 200m
          max: 800m
        memory:
          limit: 1750Mi
  webservers:
    config:
      resources:
        cpu:
          min: 100m
          max: 400m
        memory:
          limit: 2Gi