Bring etcd support for bucket DNS federation

- Supports centralized `config.json`
- Supports centralized `bucket` service records
  for client lookups
- implement a new proxy forwarder

cmd/config-current.go

@@ -128,9 +128,9 @@ func (s *serverConfig) GetCacheConfig() CacheConfig {
 }
 
 // Save config.
-func (s *serverConfig) Save() error {
+func (s *serverConfig) Save(configFile string) error {
 	// Save config file.
-	return quick.Save(getConfigFile(), s)
+	return quick.Save(configFile, s)
 }
 
 // Returns the string describing a difference with the given
@@ -230,7 +230,10 @@ func newServerConfig() *serverConfig {
 // found, otherwise use default parameters
 func newConfig() error {
 	// Initialize server config.
-	srvCfg := newServerConfig()
+	srvCfg, err := newQuickConfig(newServerConfig())
+	if err != nil {
+		return err
+	}
 
 	// If env is set override the credentials from config file.
 	if globalIsEnvCreds {
@@ -269,7 +272,29 @@ func newConfig() error {
 	globalServerConfigMu.Unlock()
 
 	// Save config into file.
-	return globalServerConfig.Save()
+	return globalServerConfig.Save(getConfigFile())
+}
+
+// newQuickConfig - initialize a new server config, with an allocated
+// quick.Config interface.
+func newQuickConfig(srvCfg *serverConfig) (*serverConfig, error) {
+	if globalEtcdClient == nil {
+		qcfg, err := quick.NewLocalConfig(srvCfg)
+		if err != nil {
+			return nil, err
+		}
+
+		srvCfg.Config = qcfg
+		return srvCfg, nil
+	}
+
+	qcfg, err := quick.NewEtcdConfig(srvCfg, globalEtcdClient)
+	if err != nil {
+		return nil, err
+	}
+
+	srvCfg.Config = qcfg
+	return srvCfg, nil
 }
 
 // getValidConfig - returns valid server configuration
@@ -279,7 +304,14 @@ func getValidConfig() (*serverConfig, error) {
 		Browser: true,
 	}
 
-	if _, err := quick.Load(getConfigFile(), srvCfg); err != nil {
+	var err error
+	srvCfg, err = newQuickConfig(srvCfg)
+	if err != nil {
+		return nil, err
+	}
+
+	configFile := getConfigFile()
+	if err = srvCfg.Load(configFile); err != nil {
 		return nil, err
 	}