added etcd support

pkg/cluster/cluster.go

@@ -8,7 +8,8 @@ import (
 )
 
 type Cluster interface {
-	Start(logr.Logger, *config.Config) error
+	Start(*config.Config) error
+	SetCallbacks(Callbacks) error
 	Stepdown()
 	Stop()
 }
@@ -19,7 +20,13 @@ type KV interface {
 	Delete(k string) error
 }
 
-type Callbacks struct {
-	Leader   func(context.Context, KV)
-	Follower func(context.Context, KV)
+type CallbackContext interface {
+	logr.Logger
+	KV
+	ID() string
+}
+
+type Callbacks struct {
+	Leader   func(context.Context, CallbackContext)
+	Follower func(context.Context, CallbackContext)
 }