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)
+}