nats-io/nats-server · error

Evicted peers %+v, cluster size is now %d

Error message

Evicted peers %+v, cluster size is now %d

What it means

Informational membership event: after a peer-state change, peers absent from the advertised peer list (and not self, and not emptying the group) were evicted via removePeer — marked so they cannot rejoin automatically, with cluster size and quorum adjusted. The new cluster size is logged.

Source

Thrown at server/raft.go:1222

		(slices.Contains(peers, n.membChange.peer) || n.pendingSelfRemoval()) {
		n.revertMembershipChange()
	}
	var evicted []string
	for _, peer := range peers {
		// Never evict ourselves, and never empty out the group.
		if peer == n.id || len(n.peers) <= 1 {
			continue
		}
		if _, ok := n.peers[peer]; !ok {
			continue
		}
		// Marks the peer as removed so it can not rejoin or be re-added
		// automatically, adjusts cluster size and quorum, and persists.
		n.removePeer(peer)
		evicted = append(evicted, peer)
	}
	if len(evicted) > 0 {
		n.warn("Evicted peers %+v, cluster size is now %d", evicted, n.csz)
	}
	return evicted, nil
}

func (n *raft) MembershipChangeInProgress() bool {
	n.RLock()
	defer n.RUnlock()
	return n.membChange != nil
}

// pendingSelfRemoval reports whether we have an uncommitted removal of ourselves.
// We're speculatively dropped from our own peer set at append time, but the meta
// layer can still consider us a member until the removal commits.
// Lock should be held.
func (n *raft) pendingSelfRemoval() bool {
	// A removal tracks the previous membership state, an addition does not.
	return n.membChange != nil && n.membChange.peer == n.id && n.membChange.prev != nil
}

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Verify the eviction was expected (e.g. planned peer removal)
2. Re-add an evicted peer explicitly if it was unintentional
3. Check cluster size remains adequate for quorum after evictions

When it happens

Trigger: Thrown at server/raft.go:1222 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/7fb507df6e9759f0. Report an issue: GitHub.