cluster: add etcd based leader elector and factory

cluster/factory.go

@@ -0,0 +1,37 @@
+package cluster
+
+import (
+	"context"
+	"fmt"
+)
+
+// leaderElectorFactoryFunc is a LeaderElector factory method type.
+type leaderElectorFactoryFunc func(context.Context, ...interface{}) (
+	LeaderElector, error)
+
+var leaderElectorFactories map[string]leaderElectorFactoryFunc
+
+// RegisterLeaderElectorFactory will register a new LeaderElector factory
+// method corresponding to the passed id.
+func RegisterLeaderElectorFactory(id string, factory leaderElectorFactoryFunc) {
+	if leaderElectorFactories == nil {
+		leaderElectorFactories = make(
+			map[string]leaderElectorFactoryFunc,
+		)
+	}
+
+	leaderElectorFactories[id] = factory
+}
+
+// MakeLeaderElector will constuct a LeaderElector identified by id with the
+// passed arguments.
+func MakeLeaderElector(ctx context.Context, id string, args ...interface{}) (
+	LeaderElector, error) {
+
+	if _, ok := leaderElectorFactories[id]; !ok {
+		return nil, fmt.Errorf("leader elector factory for '%v' "+
+			"not found", id)
+	}
+
+	return leaderElectorFactories[id](ctx, args...)
+}