feat(auto-scale-up): add fake online, server status cache, and seamless connection during scale-up

cmd/mc-router/main.go

@@ -71,6 +71,12 @@ type Config struct {
 
 	SimplifySRV bool `default:"false" usage:"Simplify fully qualified SRV records for mapping"`
 
+	FakeOnline     bool   `default:"false" usage:"Enable fake online MOTD when backend is offline and auto-scale-up is enabled"`
+	FakeOnlineMOTD string `default:"Server is sleeping\nJoin to wake it up" usage:"Custom MOTD to show when backend is offline and auto-scale-up is enabled"`
+
+	CacheStatus         bool   `default:"false" usage:"Cache status response for backends"`
+	CacheStatusInterval string `default:"30s" usage:"Interval to update the status cache"`
+
 	Webhook WebhookConfig `usage:"Webhook configuration"`
 }
 
@@ -138,7 +144,6 @@ func main() {
 	// Only one instance should be created
 	server.DownScaler = server.NewDownScaler(ctx, downScalerEnabled, downScalerDelay)
 
-
 	c := make(chan os.Signal, 1)
 	signal.Notify(c, syscall.SIGINT, syscall.SIGTERM)
 
@@ -167,7 +172,21 @@ func main() {
 		trustedIpNets = append(trustedIpNets, ipNet)
 	}
 
-	connector := server.NewConnector(metricsBuilder.BuildConnectorMetrics(), config.UseProxyProtocol, config.ReceiveProxyProtocol, trustedIpNets, config.RecordLogins, autoScaleAllowDenyConfig)
+	fakeOnlineEnabled := config.FakeOnline && config.AutoScale.Up && (config.InKubeCluster || config.KubeConfig != "")
+
+	connectorConfig := server.ConnectorConfig{
+		SendProxyProto:             config.UseProxyProtocol,
+		ReceiveProxyProto:          config.ReceiveProxyProtocol,
+		TrustedProxyNets:           trustedIpNets,
+		RecordLogins:               config.RecordLogins,
+		AutoScaleUpAllowDenyConfig: autoScaleAllowDenyConfig,
+		AutoScaleUp:                config.AutoScale.Up,
+		FakeOnline:                 fakeOnlineEnabled,
+		FakeOnlineMOTD:             config.FakeOnlineMOTD,
+		CacheStatus:                config.CacheStatus,
+	}
+
+	connector := server.NewConnector(metricsBuilder.BuildConnectorMetrics(), connectorConfig)
 
 	clientFilter, err := server.NewClientFilter(config.ClientsToAllow, config.ClientsToDeny)
 	if err != nil {
@@ -184,6 +203,15 @@ func main() {
 			server.NewWebhookNotifier(config.Webhook.Url, config.Webhook.RequireUser))
 	}
 
+	var cacheInterval time.Duration
+	if config.CacheStatus {
+		cacheInterval, err = time.ParseDuration(config.CacheStatusInterval)
+		if err != nil {
+			logrus.WithError(err).Fatal("Unable to parse cache status interval")
+		}
+		logrus.WithField("interval", config.CacheStatusInterval).Info("Using cache status interval")
+	}
+
 	if config.NgrokToken != "" {
 		connector.UseNgrok(config.NgrokToken)
 	}
@@ -240,6 +268,15 @@ func main() {
 		logrus.WithError(err).Fatal("Unable to start metrics reporter")
 	}
 
+	if config.CacheStatus {
+		logrus.Info("Starting status cache updater")
+		connector.StatusCache.StartUpdater(connector, cacheInterval, func() map[string]string {
+			mappings := server.Routes.GetMappings()
+			logrus.WithField("mappings", mappings).Debug("Status cache updater")
+			return mappings
+		})
+	}
+
 	// wait for process-stop signal
 	<-c
 	logrus.Info("Stopping. Waiting for connections to complete...")

go.mod

@@ -23,6 +23,7 @@ require (
 )
 
 require (
+	github.com/Raqbit/mc-pinger v0.2.4 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/containerd/log v0.1.0 // indirect
@@ -50,6 +51,7 @@ require (
 	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/common v0.62.0 // indirect
 	github.com/prometheus/procfs v0.15.1 // indirect
+	github.com/sethvargo/go-retry v0.3.0 // indirect
 	github.com/x448/float16 v0.8.4 // indirect
 	go.opentelemetry.io/auto/sdk v1.1.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.47.0 // indirect

mcproto/types.go

@@ -84,3 +84,30 @@ type ByteReader interface {
 const (
 	PacketLengthFieldBytes = 1
 )
+
+type StatusResponse struct {
+	Version     StatusVersion `json:"version"`
+	Players     StatusPlayers `json:"players"`
+	Description StatusText    `json:"description"`
+	Favicon     string        `json:"favicon,omitempty"`
+}
+
+type StatusVersion struct {
+	Name     string `json:"name"`
+	Protocol int    `json:"protocol"`
+}
+
+type StatusPlayers struct {
+	Max    int           `json:"max"`
+	Online int           `json:"online"`
+	Sample []PlayerEntry `json:"sample,omitempty"`
+}
+
+type PlayerEntry struct {
+	Name string `json:"name"`
+	ID   string `json:"id"`
+}
+
+type StatusText struct {
+	Text string `json:"text"`
+}

mcproto/write.go

@@ -0,0 +1,41 @@
+package mcproto
+
+import (
+	"encoding/json"
+	"io"
+)
+
+func WriteStatusResponse(w io.Writer, status *StatusResponse) error {
+	data, err := json.Marshal(status)
+	if err != nil {
+		return err
+	}
+
+	jsonLen := encodeVarInt(len(data))
+	payload := append(jsonLen, data...)
+	return WritePacket(w, 0x00, payload)
+}
+
+func WritePacket(w io.Writer, packetID int, data []byte) error {
+	packet := append(encodeVarInt(packetID), data...)
+	length := encodeVarInt(len(packet))
+	_, err := w.Write(append(length, packet...))
+	return err
+}
+
+// encodeVarInt encodes an int as a Minecraft VarInt.
+func encodeVarInt(value int) []byte {
+	var buf []byte
+	for {
+		temp := byte(value & 0x7F)
+		value >>= 7
+		if value != 0 {
+			temp |= 0x80
+		}
+		buf = append(buf, temp)
+		if value == 0 {
+			break
+		}
+	}
+	return buf
+}

server/allow_deny_list.go

@@ -8,11 +8,11 @@ import (
 
 type AllowDenyLists struct {
 	Allowlist []PlayerInfo
-	Denylist []PlayerInfo
+	Denylist  []PlayerInfo
 }
 
 type AllowDenyConfig struct {
-	Global AllowDenyLists
+	Global  AllowDenyLists
 	Servers map[string]AllowDenyLists
 }
 
@@ -35,7 +35,7 @@ func entryMatchesPlayer(entry *PlayerInfo, userInfo *PlayerInfo) bool {
 	if entry.Name == "" && entry.Uuid == uuid.Nil {
 		return false
 	}
-	
+
 	if entry.Name != "" && entry.Uuid != uuid.Nil {
 		return *entry == *userInfo
 	}

server/allow_deny_list_test.go

@@ -10,7 +10,7 @@ import (
 func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 	type args struct {
 		serverAddress string
-		userInfo *PlayerInfo
+		userInfo      *PlayerInfo
 	}
 	validUserInfo := &PlayerInfo{
 		Name: "player_name",
@@ -27,20 +27,20 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 		want            bool
 	}{
 		{
-			name: "nil config",
+			name:            "nil config",
 			allowDenyConfig: nil,
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: true,
 		},
 		{
-			name: "empty config",
+			name:            "empty config",
 			allowDenyConfig: &AllowDenyConfig{},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: true,
 		},
@@ -58,7 +58,7 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 			},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: false,
 		},
@@ -73,7 +73,7 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 			},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: true,
 		},
@@ -88,7 +88,7 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 			},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: false,
 		},
@@ -103,7 +103,7 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 			},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: false,
 		},
@@ -121,7 +121,7 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 			},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: true,
 		},
@@ -138,7 +138,7 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 			},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: true,
 		},
@@ -155,7 +155,7 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 			},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: false,
 		},
@@ -172,7 +172,7 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 			},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: false,
 		},
@@ -194,7 +194,7 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 			},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: true,
 		},
@@ -216,7 +216,7 @@ func Test_allowDenyConfig_ServerAllowsPlayer(t *testing.T) {
 			},
 			args: args{
 				serverAddress: "server.my.domain",
-				userInfo: validUserInfo,
+				userInfo:      validUserInfo,
 			},
 			want: true,
 		},