embed/config.go
func (cfg *Config) UpdateDefaultClusterFromName(defaultInitialCluster string) (string, error) {
	if defaultHostname == "" || defaultHostStatus != nil {
		// update 'initial-cluster' when only the name is specified (e.g. 'etcd --name=abc')
		if cfg.Name != DefaultName && cfg.InitialCluster == defaultInitialCluster {
			cfg.InitialCluster = cfg.InitialClusterFromName(cfg.Name)
		}
		return "", defaultHostStatus
	}

	used := false
	pip, pport := cfg.LPUrls[0].Hostname(), cfg.LPUrls[0].Port()
	if cfg.defaultPeerHost() && pip == "0.0.0.0" {
		cfg.APUrls[0] = url.URL{Scheme: cfg.APUrls[0].Scheme, Host: fmt.Sprintf("%s:%s", defaultHostname, pport)}
		used = true
	}
	// update 'initial-cluster' when only the name is specified (e.g. 'etcd --name=abc')
	if cfg.Name != DefaultName && cfg.InitialCluster == defaultInitialCluster {
		cfg.InitialCluster = cfg.InitialClusterFromName(cfg.Name)
	}

	cip, cport := cfg.LCUrls[0].Hostname(), cfg.LCUrls[0].Port()
	if cfg.defaultClientHost() && cip == "0.0.0.0" {
		cfg.ACUrls[0] = url.URL{Scheme: cfg.ACUrls[0].Scheme, Host: fmt.Sprintf("%s:%s", defaultHostname, cport)}
		used = true
	}
	dhost := defaultHostname
	if !used {
		dhost = ""
	}
	return dhost, defaultHostStatus
}
func (cfg *Config) UpdateDefaultClusterFromName(defaultInitialCluster string) (string, error) {
	if defaultHostname == "" || defaultHostStatus != nil {
		// update 'initial-cluster' when only the name is specified (e.g. 'etcd --name=abc')
		if cfg.Name != DefaultName && cfg.InitialCluster == defaultInitialCluster {
			cfg.InitialCluster = cfg.InitialClusterFromName(cfg.Name)
		}
		return "", defaultHostStatus
	}

	used := false
	pip, pport := cfg.LPUrls[0].Hostname(), cfg.LPUrls[0].Port()
	if cfg.defaultPeerHost() && pip == "0.0.0.0" {
		cfg.APUrls[0] = url.URL{Scheme: cfg.APUrls[0].Scheme, Host: fmt.Sprintf("%s:%s", defaultHostname, pport)}
		used = true
	}
	// update 'initial-cluster' when only the name is specified (e.g. 'etcd --name=abc')
	if cfg.Name != DefaultName && cfg.InitialCluster == defaultInitialCluster {
		cfg.InitialCluster = cfg.InitialClusterFromName(cfg.Name)
	}

	cip, cport := cfg.LCUrls[0].Hostname(), cfg.LCUrls[0].Port()
	if cfg.defaultClientHost() && cip == "0.0.0.0" {
		cfg.ACUrls[0] = url.URL{Scheme: cfg.ACUrls[0].Scheme, Host: fmt.Sprintf("%s:%s", defaultHostname, cport)}
		used = true
	}
	dhost := defaultHostname
	if !used {
		dhost = ""
	}
	return dhost, defaultHostStatus
}
// UpdateDefaultClusterFromName updates cluster advertise URLs with, if available, default host,
// if advertise URLs are default values(localhost:2379,2380) AND if listen URL is 0.0.0.0.
// e.g. advertise peer URL localhost:2380 or listen peer URL 0.0.0.0:2380
// then the advertise peer host would be updated with machine's default host,
// while keeping the listen URL's port.
// User can work around this by explicitly setting URL with 127.0.0.1.
// It returns the default hostname, if used, and the error, if any, from getting the machine's default host.
// TODO: check whether fields are set instead of whether fields have default value