nats-io/nats-server · error

cluster name is reserved

Error message

cluster name is reserved

What it means

The peer's advertised cluster name equals the reserved internal value used to denote 'no origin cluster' on leaf node connections; using it explicitly is forbidden, so the connection is rejected with ProtocolViolation. The proto.Cluster value in the handshake is at fault.

Source

Thrown at server/errors.go:201

	// ErrMsgHeadersNotSupported signals the parser detected a message header
	// but they are not supported on this server.
	ErrMsgHeadersNotSupported = errors.New("message headers not supported")

	// ErrNoRespondersRequiresHeaders signals that a client needs to have headers
	// on if they want no responders behavior.
	ErrNoRespondersRequiresHeaders = errors.New("no responders requires headers support")

	// ErrClusterNameConfigConflict signals that the options for cluster name in cluster and gateway are in conflict.
	ErrClusterNameConfigConflict = errors.New("cluster name conflicts between cluster and gateway definitions")

	// ErrClusterNameRemoteConflict signals that a remote server has a different cluster name.
	ErrClusterNameRemoteConflict = errors.New("cluster name from remote server conflicts")

	// ErrClusterNameHasSpaces signals that the cluster name contains spaces, which is not allowed.
	ErrClusterNameHasSpaces = errors.New("cluster name cannot contain spaces")

	// ErrClusterNameReserved signals that the cluster name is reserved for internal protocol use.
	ErrClusterNameReserved = errors.New("cluster name is reserved")

	// ErrMalformedSubject is returned when a subscription is made with a subject that does not conform to subject rules.
	ErrMalformedSubject = errors.New("malformed subject")

	// ErrSubscribePermissionViolation is returned when processing of a subscription fails due to permissions.
	ErrSubscribePermissionViolation = errors.New("subscribe permission violation")

	// ErrNoTransforms signals no subject transforms are available to map this subject.
	ErrNoTransforms = errors.New("no matching transforms available")

	// ErrCertNotPinned is returned when pinned certs are set and the certificate is not in it
	ErrCertNotPinned = errors.New("certificate not pinned")

	// ErrDuplicateServerName is returned when processing a server remote connection and
	// the server reports that this server name is already used in the cluster.
	ErrDuplicateServerName = errors.New("duplicate server name")

	// ErrMinimumVersionRequired is returned when a connection is not at the minimum version required.

View on GitHub (pinned to 3a66a489d2)

Solutions

  1. Choose a different, non-reserved cluster name
  2. Do not copy internal protocol sentinel values into user configuration
Defensive patterns

Strategy: validation

When it happens

Trigger: Thrown at server/errors.go:201 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/2a93ad921bc21ca5. Report an issue: GitHub.