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intermediateceph-mgr-failover~18 min

MGR failover - dashboard and modules temporarily down

Reported symptoms

  • ●Dashboard is unreachable
  • ●Some mgr modules stop responding
  • ●ceph mgr stat reports the active MGR is missing

Evidence

  • · ceph -s reports the cluster is HEALTH_OK (mgr does not gate the cluster)
  • · ceph orch ps shows the standby MGR taking over
  • · ceph mgr module ls reports modules enabled on the new active MGR
Diagnosis and resolutionclick to reveal

Root cause

The active MGR daemon crashed. The standby takes over; the dashboard and modules take a moment to re-register.

Remediation

Wait for the standby to take over (typically < 30s); if the standby fails to take over, ceph orch daemon start mgr.<standby-id>; verify modules re-enable.

Verification

ceph mgr stat reports a healthy active MGR; modules are enabled; the dashboard is reachable.

Prevention

Run standbys on different hosts; monitor the active MGR; rehearse MGR failover quarterly.

Architecture

The student examines the broken architecture diagram and identifies the responsible component. The cluster is running Ceph Tentacle (20.2.x); the incident is one a production operator must diagnose from the evidence presented.

Symptoms

  • Dashboard is unreachable
  • Some mgr modules stop responding
  • ceph mgr stat reports the active MGR is missing

Evidence

  • ceph -s reports the cluster is HEALTH_OK (mgr does not gate the cluster)
  • ceph orch ps shows the standby MGR taking over
  • ceph mgr module ls reports modules enabled on the new active MGR

Student investigation

The student follows the methodology: define the symptom, determine the impact, gather evidence, identify the component, form a hypothesis, test safely, restore, validate.

Progressive hints

  • Hint 1: check the cluster state with ceph -s first.
  • Hint 2: read ceph health detail and identify the affected PGs / OSDs / daemons.
  • Hint 3: use ceph osd tree, ceph pg dump, or ceph mds stat as the next-level diagnostic.
  • Hint 4: the root cause is documented in the frontmatter root_cause field.

Validation

The student runs the verification steps and confirms the symptom cleared.

Root cause

See the frontmatter root_cause field.

Remediation

Apply the fix from the frontmatter remediation field.

Prevention

Apply the prevention measures from the frontmatter prevention field.