feat: passthrough proxies

internal/proxy/server.go

@@ -157,6 +157,7 @@ func (s *Server) run(parentCtx context.Context, addrs chan net.Addr, errs chan e
 				director.ResponseTransformer(),
 			),
 			proxy.WithReverseProxyFactory(s.createReverseProxy),
+			proxy.WithDefaultHandler(http.HandlerFunc(s.handleDefault)),
 		)
 
 		r.Handle("/*", handler)
@@ -185,12 +186,21 @@ func (s *Server) createReverseProxy(ctx context.Context, target *url.URL) *httpu
 	httpTransport.DialContext = dialer.DialContext
 
 	reverseProxy.Transport = httpTransport
-	reverseProxy.ErrorHandler = s.errorHandler
+	reverseProxy.ErrorHandler = s.handleError
 
 	return reverseProxy
 }
 
-func (s *Server) errorHandler(w http.ResponseWriter, r *http.Request, err error) {
+func (s *Server) handleDefault(w http.ResponseWriter, r *http.Request) {
+	err := errors.Errorf("no proxy target found")
+
+	logger.Error(r.Context(), "proxy error", logger.E(err))
+	sentry.CaptureException(err)
+
+	s.renderErrorPage(w, r, err, http.StatusBadGateway, http.StatusText(http.StatusBadGateway))
+}
+
+func (s *Server) handleError(w http.ResponseWriter, r *http.Request, err error) {
 	err = errors.WithStack(err)
 
 	logger.Error(r.Context(), "proxy error", logger.E(err))