Improve Node Failure Handling By Automatically Force Delete Terminating Pods of StatefulSet/Deployment On Downed Node

  1. Setup a cluster of 3 worker nodes
  2. Install Longhorn and set Default Replica Count = 2 (because we will turn off one node)
  3. Create a StatefulSet with 2 pods using the command: 
    kubectl create -f https://raw.githubusercontent.com/longhorn/longhorn/master/examples/statefulset.yaml
  4. Create a volume + pv + pvc named vol1 and create a deployment(1 pod) of default ubuntu named shell with the usage of pvc vol1 mounted under /mnt/vol1
  5. Find the node which contains one pod of the StatefulSet/Deployment. Power off the node

StatefulSet

if NodeDownPodDeletionPolicy is set to do-nothing | delete-deployment-pod
  • wait till the pod.deletionTimestamp has passed
  • verify no replacement pod generated, the pod is stuck at terminating forever.
if NodeDownPodDeletionPolicy is set to delete-statefulset-pod | delete-both-statefulset-and-deployment-pod
  • wait till pod’s status becomes terminating and the pod.deletionTimestamp has passed (around 7 minutes)
  • verify that the pod is deleted and there is a new running replacement pod.
  • Verify that you can access/read/write the volume on the new pod

Deployment

if NodeDownPodDeletionPolicy is set to do-nothing | delete-statefulset-pod
  • wait till the pod.deletionTimestamp has passed
  • replacement pod will be stuck in Pending state forever
  • force delete the terminating pod
  • wait till replacement pod is running
  • verify that you can access vol1 via the shell replacement pod under /mnt/vol1 once it is in the running state
if NodeDownPodDeletionPolicy is set to delete-deployment-pod | delete-both-statefulset-and-deployment-pod
  • wait till the pod.deletionTimestamp has passed
  • verify that the pod is deleted and there is a new running replacement pod.
  • verify that you can access vol1 via the shell replacement pod under /mnt/vol1

Other kinds

  • Verify that Longhorn never deletes any other pod on the downed node.

Test example

One typical scenario when the enhancement has succeeded is as below. When a node (say node-x) goes down (assume using Kubernetes’ default settings and user allows Longhorn to force delete pods):

Time Event
0m:00s node-xgoes down and stops sending heartbeats to Kubernetes Node controller
0m:40s Kubernetes Node controller reports node-x is NotReady.
5m:40s Kubernetes Node controller starts evicting pods from node-x using graceful termination (set DeletionTimestamp and deletionGracePeriodSeconds = 10s/30s)
5m:50s/6m:10s Longhorn forces delete the pod of StatefulSet/Deployment which uses Longhorn volume
[Edit]