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Volume Eviction

Volume eviction/migration is one of most important funcions in the HwameiStor, especially in the production environment. HwameiStor will keep the data in the volume when migrate it.

Once a Kubernetes node or pod is evicted by the system for any reason, HwameiStor will detect all the volume replicas located on this node, and automatically migrate them to other avaliable nodes. So that, the evicted pods can be rescheduled to another node and continue to run.

Node Eviction

In a Kubernetes cluster, a node can be drained by using the following procedure. So that, all the pods and volume replicas on this node will be evicted, and then continue the services on other avaliable nodes.

kubectl drain k8s-node-1 --ignore-daemonsets=true

Check if all the volumes' migration complete or not by running:

kubectl get LocalStorageNode k8s-node-1 -o yaml

The output may look like:

kind: LocalStorageNode
creationTimestamp: "2022-10-11T07:41:58Z"
generation: 1
name: k8s-node-1
resourceVersion: "6402198"
uid: c71cc6ac-566a-4e0b-8687-69679b07471f
hostname: k8s-node-1
region: default
zone: default
class: HDD
- capacityBytes: 17175674880
devPath: /dev/sdb
state: InUse
type: HDD
freeCapacityBytes: 16101933056
freeVolumeCount: 999
name: LocalStorage_PoolHDD
totalCapacityBytes: 17175674880
totalVolumeCount: 1000
usedCapacityBytes: 1073741824
usedVolumeCount: 1
volumeCapacityBytesLimit: 17175674880
# ** make sure volumes is empty ** #
state: Ready

Check if there is any volume replica still located in the evicted node by running:

kubectl get localvolumereplica

The output may look like:

NAME                                              CAPACITY     NODE         STATE   SYNCED   DEVICE                                                                  AGE
pvc-1427f36b-adc4-4aef-8d83-93c59064d113-957f7g 1073741824 k8s-node-3 Ready true /dev/LocalStorage_PoolHDD-HA/pvc-1427f36b-adc4-4aef-8d83-93c59064d113 20h
pvc-1427f36b-adc4-4aef-8d83-93c59064d113-qlpbmq 1073741824 k8s-node-2 Ready true /dev/LocalStorage_PoolHDD-HA/pvc-1427f36b-adc4-4aef-8d83-93c59064d113 30m
pvc-6ca4c0d4-da10-4e2e-83b2-19cbf5c5e3e4-scrxjb 1073741824 k8s-node-2 Ready true /dev/LocalStorage_PoolHDD/pvc-6ca4c0d4-da10-4e2e-83b2-19cbf5c5e3e4 30m
pvc-f8f017f9-eb09-4fbe-9795-a6e2d6873148-5t782b 1073741824 k8s-node-2 Ready true /dev/LocalStorage_PoolHDD-HA/pvc-f8f017f9-eb09-4fbe-9795-a6e2d6873148 30m

In some cases, user doesn't want to migrate the volumes when draining a node. User can add a label into the node before draining it.

kubectl label node k8s-node-1

Pod Eviction

When a Kubernetes node is overloaded, it will evict some low-priority pods to recycle system's resources to keep other pods safe. HwameiStor will detect the evicted pod and migrate the associated volumes to another available node. So that, the pod can continue to run on it.

Pod Migration

The migration can be pro-actively triggered on the pod and associated HwameiStor volume by using either one of following methods.

  • Method #1

    kubectl label pod mysql-pod
    kubectl delete pod mysql-pod
  • Method #2

    $ cat << EOF | kubectl apply -f -
    kind: LocalVolumeMigrate
    name: migrate-pvc-6ca4c0d4-da10-4e2e-83b2-19cbf5c5e3e4
    sourceNode: k8s-node-1
    - k8s-node-2
    - k8s-node-3
    volumeName: pvc-6ca4c0d4-da10-4e2e-83b2-19cbf5c5e3e4
    migrateAllVols: true

    $ kubectl delete pod mysql-pod