chore: add test for coord rolling restart (#14680)

Closes https://github.com/coder/team-coconut/issues/50

---------

Co-authored-by: Ethan Dickson <ethan@coder.com>

coderd/coderd.go

@@ -1485,9 +1485,6 @@ func (api *API) Close() error {
 	default:
 		api.cancel()
 	}
-	if api.derpCloseFunc != nil {
-		api.derpCloseFunc()
-	}
 
 	wsDone := make(chan struct{})
 	timer := time.NewTimer(10 * time.Second)
@@ -1513,11 +1510,16 @@ func (api *API) Close() error {
 		api.updateChecker.Close()
 	}
 	_ = api.workspaceAppServer.Close()
+	_ = api.agentProvider.Close()
+	if api.derpCloseFunc != nil {
+		api.derpCloseFunc()
+	}
+	// The coordinator should be closed after the agent provider, and the DERP
+	// handler.
 	coordinator := api.TailnetCoordinator.Load()
 	if coordinator != nil {
 		_ = (*coordinator).Close()
 	}
-	_ = api.agentProvider.Close()
 	_ = api.statsReporter.Close()
 	_ = api.NetworkTelemetryBatcher.Close()
 	_ = api.OIDCConvertKeyCache.Close()

coderd/tailnet.go

@@ -75,7 +75,8 @@ func NewServerTailnet(
 	// given in this callback, it's only valid while connecting.
 	if derpServer != nil {
 		conn.SetDERPRegionDialer(func(_ context.Context, region *tailcfg.DERPRegion) net.Conn {
-			if !region.EmbeddedRelay {
+			// Don't set up the embedded relay if we're shutting down
+			if !region.EmbeddedRelay || ctx.Err() != nil {
 				return nil
 			}
 			logger.Debug(ctx, "connecting to embedded DERP via in-memory pipe")