Applicable versions

All Longhorn versions.

Background

Let’s say you have a cluster of 5 nodes (node-1, node-2, …, node-5). You have some fast disks on node-1, node-2, and node-3 so you want Longhorn to use storage on those nodes only. There are a few ways to do this as below.

Tell Longhorn to create a default disk on a specific set of nodes

• Label node-1, node-2, and node-3 with label node.longhorn.io/create-default-disk=true (e.g., kubectl label nodes node-1 node.longhorn.io/create-default-disk=true)
• Install Longhorn with the setting Create Default Disk on Labeled Nodes set to true.

Result: workloads that use Longhorn volumes can run on any nodes. Longhorn only uses storage on node-1, node-2, and node-3 for replica scheduling.

Create a StorageClass that select a specific set of nodes

• Install Longhorn normally on all nodes
• Go to the node page on Longhorn UI, tag the node node-1, node-2, and node-3 with a tag, e.g., storage
• Create a new StorageClass that have node selector nodeSelector: "storage" . E.g.,

  kind: StorageClass
  apiVersion: storage.k8s.io/v1
  metadata:
    name: my-longhorn-sc
  provisioner: driver.longhorn.io
  allowVolumeExpansion: true
  reclaimPolicy: Delete
  volumeBindingMode: Immediate
  parameters:
    numberOfReplicas: "3"
    staleReplicaTimeout: "2880" # 48 hours in minutes
    fromBackup: ""
    fsType: "ext4"
    nodeSelector: "storage"
  

• Use the StorageClass my-longhorn-sc for the PVCs of workload. E.g.,

  apiVersion: v1
  kind: PersistentVolumeClaim
  metadata:
    name: my-longhorn-volv-pvc
  spec:
    accessModes:
      - ReadWriteOnce
    storageClassName: my-longhorn-s
    resources:
      requests:
        storage: 2Gi
  

Result: workloads that use Longhorn volumes can run on any nodes. Longhorn only schedules replicas of my-longhorn-volv-pvc on the node node-1, node-2, and node-3

Deploy Longhorn components only on a specific set of nodes

• Label node-1, node-2, and node-3 with label storage=longhorn (e.g., kubectl label nodes node-1 storage=longhorn)
• Set node selector for Longhorn components by following the instruction to deploy Longhorn components only on node with label storage=longhorn

Result: Longhorn components are only deployed on node-1, node-2, and node-3. Workloads that use Longhorn volumes can only be scheduled on node-1, node-2, and node-3.