TUN-6617: Dont fallback to http2 if QUIC conn was successful.

cloudflared falls back aggressively to HTTP/2 protocol if a connection
attempt with QUIC failed. This was done to ensure that machines with UDP
egress disabled did not stop clients from connecting to the cloudlfare
edge. This PR improves on that experience by having cloudflared remember
if a QUIC connection was successful which implies UDP egress works. In
this case, cloudflared does not fallback to HTTP/2 and keeps trying to
connect to the edge with QUIC.

supervisor/conn_aware_logger.go

@@ -12,9 +12,9 @@ type ConnAwareLogger struct {
 	logger  *zerolog.Logger
 }
 
-func NewConnAwareLogger(logger *zerolog.Logger, observer *connection.Observer) *ConnAwareLogger {
+func NewConnAwareLogger(logger *zerolog.Logger, tracker *tunnelstate.ConnTracker, observer *connection.Observer) *ConnAwareLogger {
 	connAwareLogger := &ConnAwareLogger{
-		tracker: tunnelstate.NewConnTracker(logger),
+		tracker: tracker,
 		logger:  logger,
 	}
 

supervisor/supervisor.go

@@ -19,6 +19,7 @@ import (
 	"github.com/cloudflare/cloudflared/retry"
 	"github.com/cloudflare/cloudflared/signal"
 	tunnelpogs "github.com/cloudflare/cloudflared/tunnelrpc/pogs"
+	"github.com/cloudflare/cloudflared/tunnelstate"
 )
 
 const (
@@ -88,7 +89,9 @@ func NewSupervisor(config *TunnelConfig, orchestrator *orchestration.Orchestrato
 	}
 
 	reconnectCredentialManager := newReconnectCredentialManager(connection.MetricsNamespace, connection.TunnelSubsystem, config.HAConnections)
-	log := NewConnAwareLogger(config.Log, config.Observer)
+
+	tracker := tunnelstate.NewConnTracker(config.Log)
+	log := NewConnAwareLogger(config.Log, tracker, config.Observer)
 
 	var edgeAddrHandler EdgeAddrHandler
 	if isStaticEdge { // static edge addresses
@@ -106,6 +109,7 @@ func NewSupervisor(config *TunnelConfig, orchestrator *orchestration.Orchestrato
 		credentialManager: reconnectCredentialManager,
 		edgeAddrs:         edgeIPs,
 		edgeAddrHandler:   edgeAddrHandler,
+		tracker:           tracker,
 		reconnectCh:       reconnectCh,
 		gracefulShutdownC: gracefulShutdownC,
 		connAwareLogger:   log,

supervisor/tunnel.go

@@ -26,6 +26,7 @@ import (
 	"github.com/cloudflare/cloudflared/signal"
 	"github.com/cloudflare/cloudflared/tunnelrpc"
 	tunnelpogs "github.com/cloudflare/cloudflared/tunnelrpc/pogs"
+	"github.com/cloudflare/cloudflared/tunnelstate"
 )
 
 const (
@@ -191,6 +192,7 @@ type EdgeTunnelServer struct {
 	edgeAddrs         *edgediscovery.Edge
 	reconnectCh       chan ReconnectSignal
 	gracefulShutdownC <-chan struct{}
+	tracker           *tunnelstate.ConnTracker
 
 	connAwareLogger *ConnAwareLogger
 }
@@ -273,6 +275,12 @@ func (e EdgeTunnelServer) Serve(ctx context.Context, connIndex uint8, protocolFa
 			return err
 		}
 
+		// If a single connection has connected with the current protocol, we know we know we don't have to fallback
+		// to a different protocol.
+		if e.tracker.HasConnectedWith(e.config.ProtocolSelector.Current()) {
+			return err
+		}
+
 		if !selectNextProtocol(
 			connLog.Logger(),
 			protocolFallback,
@@ -462,6 +470,7 @@ func serveTunnel(
 		nil,
 		gracefulShutdownC,
 		config.GracePeriod,
+		protocol,
 	)
 
 	switch protocol {