cluster: add cluster package skeleton and LeaderElector interface

cluster/interface.go

@@ -0,0 +1,26 @@
+package cluster
+
+import (
+	"context"
+)
+
+const (
+	// EtcdLeaderElector is the id used when constructing an
+	// etcdLeaderElector instance through the factory.
+	EtcdLeaderElector = "etcd"
+)
+
+// LeaderElector is a general interface implementing basic leader elections
+// in a clustered environment.
+type LeaderElector interface {
+	// Campaign starts a run for leadership. Campaign will block until
+	// the caller is elected as the leader.
+	Campaign(ctx context.Context) error
+
+	// Resign resigns from the leader role, allowing other election members
+	// to take on leadership.
+	Resign() error
+
+	// Leader returns the leader value for the current election.
+	Leader(ctx context.Context) (string, error)
+}

cluster/log.go

@@ -0,0 +1,27 @@
+package cluster
+
+import (
+	"github.com/btcsuite/btclog"
+	"github.com/lightningnetwork/lnd/build"
+)
+
+// Subsystem defines the logging code for this subsystem.
+const Subsystem = "CLUS"
+
+// log is a logger that is initialized with the btclog.Disabled logger.
+var log btclog.Logger
+
+// The default amount of logging is none.
+func init() {
+	UseLogger(build.NewSubLogger(Subsystem, nil))
+}
+
+// DisableLog disables all logging output.
+func DisableLog() {
+	UseLogger(btclog.Disabled)
+}
+
+// UseLogger uses a specified Logger to output package logging info.
+func UseLogger(logger btclog.Logger) {
+	log = logger
+}

log.go

@@ -14,6 +14,7 @@ import (
 	"github.com/lightningnetwork/lnd/chanfitness"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/channelnotifier"
+	"github.com/lightningnetwork/lnd/cluster"
 	"github.com/lightningnetwork/lnd/contractcourt"
 	"github.com/lightningnetwork/lnd/discovery"
 	"github.com/lightningnetwork/lnd/funding"
@@ -157,6 +158,7 @@ func SetupLoggers(root *build.RotatingLogWriter, interceptor signal.Interceptor)
 	AddSubLogger(root, chainreg.Subsystem, interceptor, chainreg.UseLogger)
 	AddSubLogger(root, chanacceptor.Subsystem, interceptor, chanacceptor.UseLogger)
 	AddSubLogger(root, funding.Subsystem, interceptor, funding.UseLogger)
+	AddSubLogger(root, cluster.Subsystem, interceptor, cluster.UseLogger)
 }
 
 // AddSubLogger is a helper method to conveniently create and register the