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longhorn/enhancements/20230601-forcibly-activate-a-restoring-dr-volume.md
James Lu 115edc0551 feat(dr-volume): force activate a dr volume LEP 
Activate a dr volume as long as there is a ready replica.

Ref: 1512

Signed-off-by: James Lu <james.lu@suse.com>
2023-06-02 14:55:40 +08:00

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Forcibly Activate A Restoring/DR Volume

Summary

When users try to activate a restoring/DR volume with some replicas failed for some reasons, the volume will be stuck in attaching state and users can not do anything except deleting the volume. However the volume still can be rebuilt back to be normal as long as there is a healthy replica.

To improve user experience, Longhorn should forcibly activate a restoring/DR volume if there is a healthy replica and users allow the creation of a degraded volume.

Related Issues

https://github.com/longhorn/longhorn/issues/1512

Motivation

Goals

Allow users to activate a restoring/DR volume as long as there is a healthy replica and the volume works well.

Non-goals [optional]

None

Proposal

Forcibly activate a restoring/DR volume if there is a healthy replica and users enable the global setting allow-volume-creation-with-degraded-availability.

User Stories

Users can activate a restoring/DR volume by the CLI kubectl or Longhorn UI and the volume could work well.

User Experience In Detail

Prerequisites

Set up two Kubernetes clusters. These will be called cluster A and cluster B. Install Longhorn on both clusters, and set the same backup target on both clusters.

  1. In the cluster A, make sure the original volume X has a backup created or has recurring backups scheduled.
  2. In backup page of cluster B, choose the backup volume X, then create disaster recovery volume Y.

Kubectl

User set volume.spec.Standby to false by editing the volume CR or the manifest creating the volume to activate the volume.

Longhorn UI

UI has click Activate Disaster Recovery Volume button in Volume or Volume Details pages to activate the volume.

API changes

None

Design

Implementation Overview

  1. Check if volume.Spec.Standby is set to false
  2. Get the global setting allow-volume-creation-with-degraded-availability
  3. Activate the DR volume if allow-volume-creation-with-degraded-availability is set to true and there are one or more ready replicas.

Test plan

Test Forcibly Activated A Restoring/DR Volume

  1. Create a DR volume
  2. Set the global setting concurrent-replica-rebuild-per-node-limit to be 0
  3. Failed some replicas
  4. Check if there is at least one healthy replica
  5. Call the API activate
  6. The volume could be activated
  7. Attach the volume to a node and check if data is correct

Upgrade strategy

None

Note [optional]

None