nw-metallb-operator-setting-pod-priority-affinity.adoc

Configuring pod priority and pod affinity in a MetalLB deployment

You can optionally assign pod priority and pod affinity rules to controller and speaker pods by configuring the MetalLB custom resource. The pod priority indicates the relative importance of a pod on a node and schedules the pod based on this priority. Set a high priority on your controller or speaker pod to ensure scheduling priority over other pods on the node.

Pod affinity manages relationships among pods. Assign pod affinity to the controller or speaker pods to control on what node the scheduler places the pod in the context of pod relationships. For example, you can use pod affinity rules to ensure that certain pods are located on the same node or nodes, which can help improve network communication and reduce latency between those components.

Prerequisites

• You are logged in as a user with cluster-admin privileges.

• You have installed the MetalLB Operator.

• You have started the MetalLB Operator on your cluster.

Procedure

1. Create a PriorityClass custom resource, such as myPriorityClass.yaml, to configure the priority level. This example defines a PriorityClass named high-priority with a value of 1000000. Pods that are assigned this priority class are considered higher priority during scheduling compared to pods with lower priority classes:

   apiVersion: scheduling.k8s.io/v1
   kind: PriorityClass
   metadata:
     name: high-priority
   value: 1000000

2. Apply the PriorityClass custom resource configuration:

   $ oc apply -f myPriorityClass.yaml

3. Create a MetalLB custom resource, such as MetalLBPodConfig.yaml, to specify the priorityClassName and podAffinity values:

   apiVersion: metallb.io/v1beta1
   kind: MetalLB
   metadata:
     name: metallb
     namespace: metallb-system
   spec:
     logLevel: debug
     controllerConfig:
       priorityClassName: high-priority (1)
       affinity:
         podAffinity: (2)
           requiredDuringSchedulingIgnoredDuringExecution:
           - labelSelector:
               matchLabels:
                app: metallb
             topologyKey: kubernetes.io/hostname
     speakerConfig:
       priorityClassName: high-priority
       affinity:
         podAffinity:
           requiredDuringSchedulingIgnoredDuringExecution:
           - labelSelector:
               matchLabels:
                app: metallb
             topologyKey: kubernetes.io/hostname

   1. Specifies the priority class for the MetalLB controller pods. In this case, it is set to high-priority.

   2. Specifies that you are configuring pod affinity rules. These rules dictate how pods are scheduled in relation to other pods or nodes. This configuration instructs the scheduler to schedule pods that have the label app: metallb onto nodes that share the same hostname. This helps to co-locate MetalLB-related pods on the same nodes, potentially optimizing network communication, latency, and resource usage between these pods.

4. Apply the MetalLB custom resource configuration:

   $ oc apply -f MetalLBPodConfig.yaml

Verification

• To view the priority class that you assigned to pods in the metallb-system namespace, run the following command:

  $ oc get pods -n metallb-system -o custom-columns=NAME:.metadata.name,PRIORITY:.spec.priorityClassName

  Example output

  NAME                                                 PRIORITY
  controller-584f5c8cd8-5zbvg                          high-priority
  metallb-operator-controller-manager-9c8d9985-szkqg   <none>
  metallb-operator-webhook-server-c895594d4-shjgx      <none>
  speaker-dddf7                                        high-priority

• To verify that the scheduler placed pods according to pod affinity rules, view the metadata for the pod’s node or nodes by running the following command:

  $ oc get pod -o=custom-columns=NODE:.spec.nodeName,NAME:.metadata.name -n metallb-system