Storage and resource configuration

Storage for data volumes

You can mount volumes where data is stored by specifying PersistentVolumeClaims for each individual role group:

brokers:
  roleGroups:
    default:
      config:
        resources:
          storage:
            logDirs:
              capacity: 2Gi

In the above example, all Kafka brokers in the default group store data (the location of the property log.dirs) on a 2Gi volume.

If nothing is configured in the custom resource for a certain role group, then by default each Pod has a 1Gi large local volume mount for the data location.

Resource Requests

Stackable operators handle resource requests in a sligtly different manner than Kubernetes. Resource requests are defined on role or role group level. On a role level this means that by default, 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 a 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 limit 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 Brokers has the following resource requirements:

  • 1200m CPU request

  • 3400m CPU limit

  • 2560Mi memory request and limit

  • 4Gi persistent storage

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:

brokers:
  config:
    resources:
      memory:
        limit: 1Gi
      cpu:
        min: 250m
        max: 1000m
      storage:
        logDirs:
          capacity: 2Gi
  roleGroups:
    default: