[management] Fence peer status updates with a session token (#6193)

* [management] Fence peer status updates with a session token

The connect/disconnect path used a best-effort LastSeen-after-streamStart
comparison to decide whether a status update should land. Under contention
— a re-sync arriving while the previous stream's disconnect was still in
flight, or two management replicas seeing the same peer at once — the
check was a read-then-decide-then-write window: any UPDATE in between
caused the wrong row to be written. The Go-side time.Now() that fed the
comparison also drifted under lock contention, since it was captured
seconds before the write actually committed.

Replace it with an integer-nanosecond fencing token stored alongside the
status. Every gRPC sync stream uses its open time (UnixNano) as its token.
Connects only land when the incoming token is strictly greater than the
stored one; disconnects only land when the incoming token equals the
stored one (i.e. we're the stream that owns the current session). Both
are single optimistic-locked UPDATEs — no read-then-write, no transaction
wrapper.

LastSeen is now written by the database itself (CURRENT_TIMESTAMP). The
caller never supplies it, so the value always reflects the real moment
of the UPDATE rather than the moment the caller queued the work — which
was already off by minutes under heavy lock contention.

Side effects (geo lookup, peer-login-expiration scheduling, network-map
fan-out) are explicitly documented as running after the fence UPDATE
commits, never inside it. Geo also skips the update when realIP equals
the stored ConnectionIP, dropping a redundant SavePeerLocation call on
same-IP reconnects.

Tests cover the three semantic cases (matched disconnect lands, stale
disconnect dropped, stale connect dropped) plus a 16-goroutine race test
that asserts the highest token always wins.

* [management] Add SessionStartedAt to peer status updates

Stored `SessionStartedAt` for fencing token propagation across goroutines and updated database queries/functions to handle the new field. Removed outdated geolocation handling logic and adjusted tests for concurrency safety.

* Rename `peer_status_required_approval` to `peer_status_requires_approval` in SQL store fields

management/server/store/sql_store.go

@@ -498,8 +498,9 @@ func (s *SqlStore) SavePeerStatus(ctx context.Context, accountID, peerID string,
 	peerCopy.Status = &peerStatus
 
 	fieldsToUpdate := []string{
-		"peer_status_last_seen", "peer_status_connected",
-		"peer_status_login_expired", "peer_status_required_approval",
+		"peer_status_last_seen", "peer_status_session_started_at",
+		"peer_status_connected", "peer_status_login_expired",
+		"peer_status_requires_approval",
 	}
 	result := s.db.Model(&nbpeer.Peer{}).
 		Select(fieldsToUpdate).
@@ -516,6 +517,69 @@ func (s *SqlStore) SavePeerStatus(ctx context.Context, accountID, peerID string,
 	return nil
 }
 
+// MarkPeerConnectedIfNewerSession is an atomic optimistic-locked update.
+// The peer is marked connected with the given session token only when
+// the stored SessionStartedAt is strictly smaller than the incoming
+// one — equivalently, when no newer stream has already taken ownership.
+// The sentinel zero (set on peer creation or after a disconnect) counts
+// as the smallest possible token. This is the write half of the
+// fencing protocol described on PeerStatus.SessionStartedAt.
+//
+// The post-write side effects in the caller — geo lookup,
+// schedulePeerLoginExpiration, checkAndSchedulePeerInactivityExpiration,
+// OnPeersUpdated — all run AFTER this method returns and are deliberately
+// outside the database write so they cannot extend the row-lock window.
+//
+// LastSeen is set to the database's clock (CURRENT_TIMESTAMP) at the
+// moment the row is written. The caller never supplies LastSeen because
+// the value would otherwise drift under lock contention — a Go-side
+// time.Now() taken before the write can land minutes later than the
+// actual UPDATE under load, which previously caused real ordering bugs.
+func (s *SqlStore) MarkPeerConnectedIfNewerSession(ctx context.Context, accountID, peerID string, newSessionStartedAt int64) (bool, error) {
+	result := s.db.WithContext(ctx).
+		Model(&nbpeer.Peer{}).
+		Where(accountAndIDQueryCondition, accountID, peerID).
+		Where("peer_status_session_started_at < ?", newSessionStartedAt).
+		Updates(map[string]any{
+			"peer_status_connected":          true,
+			"peer_status_last_seen":          gorm.Expr("CURRENT_TIMESTAMP"),
+			"peer_status_session_started_at": newSessionStartedAt,
+			"peer_status_login_expired":      false,
+		})
+	if result.Error != nil {
+		return false, status.Errorf(status.Internal, "mark peer connected: %v", result.Error)
+	}
+	return result.RowsAffected > 0, nil
+}
+
+// MarkPeerDisconnectedIfSameSession is an atomic optimistic-locked update.
+// The peer is marked disconnected only when the stored SessionStartedAt
+// matches the incoming token — meaning the stream that owns the current
+// session is the one ending. If a newer stream has already replaced the
+// session, the update is skipped. LastSeen is set to CURRENT_TIMESTAMP at
+// write time; see MarkPeerConnectedIfNewerSession for the rationale.
+//
+// A zero sessionStartedAt is rejected at the call site; the underlying
+// WHERE on equality would otherwise match every never-connected peer.
+func (s *SqlStore) MarkPeerDisconnectedIfSameSession(ctx context.Context, accountID, peerID string, sessionStartedAt int64) (bool, error) {
+	if sessionStartedAt == 0 {
+		return false, nil
+	}
+	result := s.db.WithContext(ctx).
+		Model(&nbpeer.Peer{}).
+		Where(accountAndIDQueryCondition, accountID, peerID).
+		Where("peer_status_session_started_at = ?", sessionStartedAt).
+		Updates(map[string]any{
+			"peer_status_connected":          false,
+			"peer_status_last_seen":          gorm.Expr("CURRENT_TIMESTAMP"),
+			"peer_status_session_started_at": int64(0),
+		})
+	if result.Error != nil {
+		return false, status.Errorf(status.Internal, "mark peer disconnected: %v", result.Error)
+	}
+	return result.RowsAffected > 0, nil
+}
+
 func (s *SqlStore) SavePeerLocation(ctx context.Context, accountID string, peerWithLocation *nbpeer.Peer) error {
 	// To maintain data integrity, we create a copy of the peer's location to prevent unintended updates to other fields.
 	var peerCopy nbpeer.Peer
@@ -1723,9 +1787,10 @@ func (s *SqlStore) getPeers(ctx context.Context, accountID string) ([]nbpeer.Pee
 	inactivity_expiration_enabled, last_login, created_at, ephemeral, extra_dns_labels, allow_extra_dns_labels, meta_hostname,
 	meta_go_os, meta_kernel, meta_core, meta_platform, meta_os, meta_os_version, meta_wt_version, meta_ui_version,
 	meta_kernel_version, meta_network_addresses, meta_system_serial_number, meta_system_product_name, meta_system_manufacturer,
-	meta_environment, meta_flags, meta_files, meta_capabilities, peer_status_last_seen, peer_status_connected, peer_status_login_expired,
-	peer_status_requires_approval, location_connection_ip, location_country_code, location_city_name,
-	location_geo_name_id, proxy_meta_embedded, proxy_meta_cluster, ipv6 FROM peers WHERE account_id = $1`
+	meta_environment, meta_flags, meta_files, meta_capabilities, peer_status_last_seen, peer_status_session_started_at,
+	peer_status_connected, peer_status_login_expired, peer_status_requires_approval, location_connection_ip,
+	location_country_code, location_city_name, location_geo_name_id, proxy_meta_embedded, proxy_meta_cluster, ipv6
+	FROM peers WHERE account_id = $1`
 	rows, err := s.pool.Query(ctx, query, accountID)
 	if err != nil {
 		return nil, err
@@ -1738,6 +1803,7 @@ func (s *SqlStore) getPeers(ctx context.Context, accountID string) ([]nbpeer.Pee
 			lastLogin, createdAt                                                                            sql.NullTime
 			sshEnabled, loginExpirationEnabled, inactivityExpirationEnabled, ephemeral, allowExtraDNSLabels sql.NullBool
 			peerStatusLastSeen                                                                              sql.NullTime
+			peerStatusSessionStartedAt                                                                      sql.NullInt64
 			peerStatusConnected, peerStatusLoginExpired, peerStatusRequiresApproval, proxyEmbedded          sql.NullBool
 			ip, extraDNS, netAddr, env, flags, files, capabilities, connIP, ipv6                            []byte
 			metaHostname, metaGoOS, metaKernel, metaCore, metaPlatform                                      sql.NullString
@@ -1752,8 +1818,9 @@ func (s *SqlStore) getPeers(ctx context.Context, accountID string) ([]nbpeer.Pee
 			&allowExtraDNSLabels, &metaHostname, &metaGoOS, &metaKernel, &metaCore, &metaPlatform,
 			&metaOS, &metaOSVersion, &metaWtVersion, &metaUIVersion, &metaKernelVersion, &netAddr,
 			&metaSystemSerialNumber, &metaSystemProductName, &metaSystemManufacturer, &env, &flags, &files, &capabilities,
-			&peerStatusLastSeen, &peerStatusConnected, &peerStatusLoginExpired, &peerStatusRequiresApproval, &connIP,
-			&locationCountryCode, &locationCityName, &locationGeoNameID, &proxyEmbedded, &proxyCluster, &ipv6)
+			&peerStatusLastSeen, &peerStatusSessionStartedAt, &peerStatusConnected, &peerStatusLoginExpired,
+			&peerStatusRequiresApproval, &connIP, &locationCountryCode, &locationCityName, &locationGeoNameID,
+			&proxyEmbedded, &proxyCluster, &ipv6)
 
 		if err == nil {
 			if lastLogin.Valid {
@@ -1780,6 +1847,9 @@ func (s *SqlStore) getPeers(ctx context.Context, accountID string) ([]nbpeer.Pee
 			if peerStatusLastSeen.Valid {
 				p.Status.LastSeen = peerStatusLastSeen.Time
 			}
+			if peerStatusSessionStartedAt.Valid {
+				p.Status.SessionStartedAt = peerStatusSessionStartedAt.Int64
+			}
 			if peerStatusConnected.Valid {
 				p.Status.Connected = peerStatusConnected.Bool
 			}