nats-io/nats-server · error

Unsafe quorum rescue applied, quorum lowered %d -> %d for %v

Error message

Unsafe quorum rescue applied, quorum lowered %d -> %d for %v

What it means

An operator-driven RescueQuorum lowered the quorum from the natural value to qn for a bounded rescueQuorumTimeout, allowing elections/commits on a degraded cluster. A timer auto-expires the rescue; while active, recalcQuorum preserves the lowered value. This is deliberately unsafe: commits may lack durable majority.

Source

Thrown at server/raft.go:1361

	// If all servers are empty, this requires a cluster bootstrap.
	if n.pindex == 0 {
		return prev, 0, errRescueEmptyLog
	}

	// Cancel any previous rescue.
	if n.rescue != nil {
		n.rescue.Stop()
	}
	var t *time.Timer
	t = time.AfterFunc(rescueQuorumTimeout, func() {
		n.Lock()
		defer n.Unlock()
		// Read of t must be under the lock.
		n.expireRescueLocked(t)
	})
	n.rescue = t
	n.qn = qn
	n.warn("Unsafe quorum rescue applied, quorum lowered %d -> %d for %v", prev, qn, rescueQuorumTimeout)

	// Make sure an election can happen soon.
	n.resetElect(randCampaignTimeout())
	return prev, qn, nil
}

// expireRescueLocked runs when the rescue timeout fires and restores the natural quorum.
// Lock should be held.
func (n *raft) expireRescueLocked(t *time.Timer) {
	if n.State() == Closed || n.rescue != t {
		return
	}
	// Must clear the timer first, recalcQuorum keeps the rescued quorum
	// while it sees an active rescue.
	n.rescue = nil
	n.recalcQuorum()
	n.warn("Unsafe quorum rescue expired, quorum restored to %d", n.qn)
}

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Restore missing peers before the rescue timeout expires to avoid split-brain risk
2. Back up RAFT state before using rescue on production clusters
3. Monitor for the 'rescue expired' log to know when normal quorum returned

When it happens

Trigger: Thrown at server/raft.go:1361 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/eda15740b72cbda7. Report an issue: GitHub.