Volume Health Monitoring Feature

Status

Overview

The External Health Monitor is part of Kubernetes implementation of Container Storage Interface (CSI). It was introduced as an Alpha feature in Kubernetes v1.19.

The External Health Monitor is implemented as two components: External Health Monitor Controller and External Health Monitor Agent.

• External Health Monitor Controller:

  • The external health monitor controller will be deployed as a sidecar together with the CSI controller driver, similar to how the external-provisioner sidecar is deployed.
  • Trigger controller RPC to check the health condition of the CSI volumes.
  • The external controller sidecar will also watch for node failure events. This component can be enabled by setting the enable-node-watcher flag to true. This will only have effects on local PVs now. When a node failure event is detected, an event will be reported on the PVC to indicate that pods using this PVC are on a failed node.

• External Health Monitor Agent:

  • The external health monitor agent will be deployed as a sidecar together with the CSI node driver on every Kubernetes worker node.
  • Trigger node RPC to check volume's mounting conditions.

The External Health Monitor needs to invoke the following CSI interfaces

• External Health Monitor Controller:
  • ListVolumes
  • ControllerGetVolume
• External Health Monitor Agent:
  • NodeGetVolumeStats

The External Health Monitor Controller calls either ListVolumes or ControllerGetVolume CSI RPC and reports VolumeConditionAbnormal events with messages on PVCs if abnormal volume conditions are detected.

The External Health Monitor Agent calls NodeGetVolumeStats CSI RPC and reports VolumeConditionAbnormal events with messages on Pods if abnormal volume conditions are detected.

See external-health-monitor-controller.md for more details on the CSI external-health-monitor-controller sidecar.

See external-health-monitor-agent.md for more details on the CSI external-health-monitor-agent sidecar.