fix(dynamic): check all backends for load-balanced servers

Previously, checkServerConnectivity only checked the first backend
address (from ServerInfo.Addr()), which could fail if that specific
backend was unreachable from the proxy's network.

Now checks all backends for load-balanced servers - if ANY backend
is reachable via MC ping, the server is considered ready. This fixes
timeout issues when the first backend is unreachable but others are
available (e.g., remote address fails but localhost succeeds).

For regular (non-load-balanced) servers, behavior is unchanged.

Author: Trirrin

internal/dynamicserver/manager.go

@@ -10,6 +10,7 @@ import (
 	"github.com/go-logr/logr"
 	"go.minekube.com/gate/pkg/edition/java/proxy"
 
+	"github.com/RMS-Server/RMS-Gate/internal/loadbalancer"
 	"github.com/RMS-Server/RMS-Gate/internal/mcsmanager"
 	"github.com/RMS-Server/RMS-Gate/internal/minecraft"
 )
@@ -185,16 +186,14 @@ func (m *Manager) waitForServerReady(serverName, instanceUUID string) bool {
 }
 
 func (m *Manager) checkServerConnectivity(serverName string) bool {
-	pollInterval := time.Duration(m.cfg.PollIntervalSeconds) * time.Second
-	maxAttempts := m.cfg.ConnectivityTimeoutSeconds / m.cfg.PollIntervalSeconds
-
 	server := m.proxy.Server(serverName)
 	if server == nil {
 		m.log.Error(nil, "Server not registered in proxy", "server", serverName)
 		return false
 	}
 
-	addr := server.ServerInfo().Addr()
+	pollInterval := time.Duration(m.cfg.PollIntervalSeconds) * time.Second
+	maxAttempts := m.cfg.ConnectivityTimeoutSeconds / m.cfg.PollIntervalSeconds
 
 	for attempt := 0; attempt < maxAttempts; attempt++ {
 		select {
@@ -203,20 +202,56 @@ func (m *Manager) checkServerConnectivity(serverName string) bool {
 		default:
 		}
 
-		err := minecraft.MCPing(addr, 3*time.Second)
-		if err == nil {
-			m.log.Info("Server is accepting connections (MC ping success)", "server", serverName)
+		// Check connectivity - try all backends if load-balanced
+		if m.checkAnyBackendReachable(server, serverName) {
 			return true
 		}
 
-		m.log.V(1).Info("Server not yet accepting connections", "server", serverName, "attempt", attempt+1, "error", err)
+		m.log.V(1).Info("Server not yet accepting connections", "server", serverName, "attempt", attempt+1)
 		time.Sleep(pollInterval)
 	}
 
 	m.log.Error(nil, "Server connectivity check timed out", "server", serverName)
 	return false
 }
 
+func (m *Manager) checkAnyBackendReachable(server proxy.RegisteredServer, serverName string) bool {
+	serverInfo := server.ServerInfo()
+
+	// Check if this is a load-balanced server with multiple backends
+	type backendProvider interface {
+		Backends() []*loadbalancer.Backend
+	}
+
+	if lbInfo, ok := serverInfo.(backendProvider); ok {
+		// Load-balanced server - check all backends
+		backends := lbInfo.Backends()
+		for _, backend := range backends {
+			addr, err := net.ResolveTCPAddr("tcp", backend.Addr)
+			if err != nil {
+				m.log.V(1).Info("Failed to resolve backend address", "backend", backend.Addr, "error", err)
+				continue
+			}
+
+			if minecraft.MCPing(addr, 3*time.Second) == nil {
+				m.log.Info("Server is accepting connections (MC ping success)",
+					"server", serverName, "backend", backend.Addr)
+				return true
+			}
+		}
+		return false
+	}
+
+	// Regular server - check single address
+	addr := serverInfo.Addr()
+	if minecraft.MCPing(addr, 3*time.Second) == nil {
+		m.log.Info("Server is accepting connections (MC ping success)",
+			"server", serverName, "addr", addr.String())
+		return true
+	}
+	return false
+}
+
 func (m *Manager) IsServerStarting(serverName string) bool {
 	m.mu.Lock()
 	defer m.mu.Unlock()