diff --git a/go/base/context.go b/go/base/context.go
index 36e279d..0ccffab 100644
--- a/go/base/context.go
+++ b/go/base/context.go
@@ -122,6 +122,7 @@ type MigrationContext struct {
 	InitiallyDropOldTable        bool
 	InitiallyDropGhostTable      bool
 	CutOverType                  CutOver
+	ReplicaServerId              uint
 
 	Hostname                               string
 	AssumeMasterHostname                   string
diff --git a/go/binlog/gomysql_reader.go b/go/binlog/gomysql_reader.go
index 6d338ca..7b57a99 100644
--- a/go/binlog/gomysql_reader.go
+++ b/go/binlog/gomysql_reader.go
@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"sync"
 
+	"github.com/github/gh-ost/go/base"
 	"github.com/github/gh-ost/go/mysql"
 	"github.com/github/gh-ost/go/sql"
 
@@ -17,10 +18,6 @@ import (
 	"github.com/siddontang/go-mysql/replication"
 )
 
-const (
-	serverId = 99999
-)
-
 type GoMySQLReader struct {
 	connectionConfig         *mysql.ConnectionConfig
 	binlogSyncer             *replication.BinlogSyncer
@@ -28,6 +25,7 @@ type GoMySQLReader struct {
 	currentCoordinates       mysql.BinlogCoordinates
 	currentCoordinatesMutex  *sync.Mutex
 	LastAppliedRowsEventHint mysql.BinlogCoordinates
+	MigrationContext         *base.MigrationContext
 }
 
 func NewGoMySQLReader(connectionConfig *mysql.ConnectionConfig) (binlogReader *GoMySQLReader, err error) {
@@ -37,7 +35,10 @@ func NewGoMySQLReader(connectionConfig *mysql.ConnectionConfig) (binlogReader *G
 		currentCoordinatesMutex: &sync.Mutex{},
 		binlogSyncer:            nil,
 		binlogStreamer:          nil,
+		MigrationContext:        base.GetMigrationContext(),
 	}
+
+	serverId := uint32(binlogReader.MigrationContext.ReplicaServerId)
 	binlogReader.binlogSyncer = replication.NewBinlogSyncer(serverId, "mysql")
 
 	return binlogReader, err
diff --git a/go/cmd/gh-ost/main.go b/go/cmd/gh-ost/main.go
index bccef88..bc6697a 100644
--- a/go/cmd/gh-ost/main.go
+++ b/go/cmd/gh-ost/main.go
@@ -104,6 +104,8 @@ func main() {
 	flag.StringVar(&migrationContext.HooksPath, "hooks-path", "", "directory where hook files are found (default: empty, ie. hooks disabled). Hook files found on this path, and conforming to hook naming conventions will be executed")
 	flag.StringVar(&migrationContext.HooksHintMessage, "hooks-hint", "", "arbitrary message to be injected to hooks via GH_OST_HOOKS_HINT, for your convenience")
 
+	flag.UintVar(&migrationContext.ReplicaServerId, "replica-server-id", 99999, "server id used by gh-ost process. Default: 99999")
+
 	maxLoad := flag.String("max-load", "", "Comma delimited status-name=threshold. e.g: 'Threads_running=100,Threads_connected=500'. When status exceeds threshold, app throttles writes")
 	criticalLoad := flag.String("critical-load", "", "Comma delimited status-name=threshold, same format as --max-load. When status exceeds threshold, app panics and quits")
 	flag.Int64Var(&migrationContext.CriticalLoadIntervalMilliseconds, "critical-load-interval-millis", 0, "When 0, migration immediately bails out upon meeting critical-load. When non-zero, a second check is done after given interval, and migration only bails out if 2nd check still meets critical load")
@@ -113,8 +115,13 @@ func main() {
 	stack := flag.Bool("stack", false, "add stack trace upon error")
 	help := flag.Bool("help", false, "Display usage")
 	version := flag.Bool("version", false, "Print version & exit")
+	checkFlag := flag.Bool("check-flag", false, "Check if another flag exists/supported. This allows for cross-version scripting. Exits with 0 when all additional provided flags exist, nonzero otherwise. You must provide (dummy) values for flags that require a value. Example: gh-ost --check-flag --cut-over-lock-timeout-seconds --nice-ratio 0")
+
 	flag.Parse()
 
+	if *checkFlag {
+		return
+	}
 	if *help {
 		fmt.Fprintf(os.Stderr, "Usage of gh-ost:\n")
 		flag.PrintDefaults()