server/ui: move UI endpoint registration below SQL initialization

HTTP requests are passed through an authentication mux, which checks
that the user is authenticated based on the cookies on the request. To
check authentication, the mux runs SQL to look up a session in the
system.web_sessions table.

Prior to this change, it was possible to hit the cluster with an HTTP
request which would cause the SQL to be run, before the SQL system was
fully initialized -- specifically before the cluster version setting was
initialized. This would crash the node.

This change delays installation of the authentication mux until after
the SQL system has been initialized, removing the possibility of this
crash.

Release note: None

pkg/server/server.go

@@ -1234,21 +1234,6 @@ func (s *Server) Start(ctx context.Context) error {
 	// endpoints.
 	s.mux.Handle(debug.Endpoint, debug.NewServer(s.st))
 
-	// Serve UI assets. This needs to be before the gRPC handlers are registered, otherwise
-	// the `s.mux.Handle("/", ...)` would cover all URLs, allowing anonymous access.
-	maybeAuthMux := newAuthenticationMuxAllowAnonymous(
-		s.authentication, ui.Handler(ui.Config{
-			ExperimentalUseLogin: s.cfg.EnableWebSessionAuthentication,
-			LoginEnabled:         s.cfg.RequireWebSession(),
-			GetUser: func(ctx context.Context) *string {
-				if u, ok := ctx.Value(webSessionUserKey{}).(string); ok {
-					return &u
-				}
-				return nil
-			},
-		}))
-	s.mux.Handle("/", maybeAuthMux)
-
 	// Initialize grpc-gateway mux and context in order to get the /health
 	// endpoint working even before the node has fully initialized.
 	jsonpb := &protoutil.JSONPb{
@@ -1537,16 +1522,6 @@ func (s *Server) Start(ctx context.Context) error {
 
 	s.serveMode.set(modeOperational)
 
-	s.mux.Handle(adminPrefix, authHandler)
-	// Exempt the health check endpoint from authentication.
-	s.mux.Handle("/_admin/v1/health", gwMux)
-	s.mux.Handle(ts.URLPrefix, authHandler)
-	s.mux.Handle(statusPrefix, authHandler)
-	s.mux.Handle(loginPath, gwMux)
-	s.mux.Handle(logoutPath, authHandler)
-	s.mux.Handle(statusVars, http.HandlerFunc(s.status.handleVars))
-	log.Event(ctx, "added http endpoints")
-
 	log.Infof(ctx, "starting %s server at %s (use: %s)",
 		s.cfg.HTTPRequestScheme(), s.cfg.HTTPAddr, s.cfg.HTTPAdvertiseAddr)
 	log.Infof(ctx, "starting grpc/postgres server at %s", s.cfg.Addr)
@@ -1609,6 +1584,33 @@ func (s *Server) Start(ctx context.Context) error {
 	log.Info(ctx, "serving sql connections")
 	// Start servicing SQL connections.
 
+	// Serve UI assets. This needs to be before the gRPC handlers are registered, otherwise
+	// the `s.mux.Handle("/", ...)` would cover all URLs, allowing anonymous access.
+	maybeAuthMux := newAuthenticationMuxAllowAnonymous(
+		s.authentication,
+		ui.Handler(ui.Config{
+			ExperimentalUseLogin: s.cfg.EnableWebSessionAuthentication,
+			LoginEnabled:         s.cfg.RequireWebSession(),
+			GetUser: func(ctx context.Context) *string {
+				if u, ok := ctx.Value(webSessionUserKey{}).(string); ok {
+					return &u
+				}
+				return nil
+			},
+		}),
+	)
+	s.mux.Handle("/", maybeAuthMux)
+
+	s.mux.Handle(adminPrefix, authHandler)
+	// Exempt the health check endpoint from authentication.
+	s.mux.Handle("/_admin/v1/health", gwMux)
+	s.mux.Handle(ts.URLPrefix, authHandler)
+	s.mux.Handle(statusPrefix, authHandler)
+	s.mux.Handle(loginPath, gwMux)
+	s.mux.Handle(logoutPath, authHandler)
+	s.mux.Handle(statusVars, http.HandlerFunc(s.status.handleVars))
+	log.Event(ctx, "added http endpoints")
+
 	// Attempt to upgrade cluster version.
 	s.startAttemptUpgrade(ctx)