Enhance mDNS Functionality

cmd/serf/command/agent/command.go

@@ -88,6 +88,9 @@ func (c *Command) readConfig() *Config {
 		"tag pair, specified as key=value")
 	cmdFlags.StringVar(&cmdConfig.Discover, "discover", "", "mDNS discovery name")
 	cmdFlags.StringVar(&cmdConfig.Interface, "iface", "", "interface to bind to")
+	cmdFlags.StringVar(&cmdConfig.MDNS.Interface, "mdns-iface", "", "interface to use for mDNS")
+	cmdFlags.BoolVar(&cmdConfig.MDNS.DisableIPv4, "mdns-disable-ipv4", false, "disable IPv4 for mDNS")
+	cmdFlags.BoolVar(&cmdConfig.MDNS.DisableIPv6, "mdns-disable-ipv6", false, "disable IPv6 for mDNS")
 	cmdFlags.StringVar(&cmdConfig.TagsFile, "tags-file", "", "tag persistence file")
 	cmdFlags.BoolVar(&cmdConfig.EnableSyslog, "syslog", false,
 		"enable logging to syslog facility")
@@ -176,6 +179,24 @@ func (c *Command) readConfig() *Config {
 		return nil
 	}
 
+	if config.MDNS.Interface != "" {
+		if config.Discover == "" {
+			c.Ui.Error("mDNS interface specified without enabling mDNS discovery")
+			return nil
+		}
+
+		if _, err := net.InterfaceByName(config.MDNS.Interface); err != nil {
+			c.Ui.Error(fmt.Sprintf("Invalid mDNS network interface: %s", err))
+			return nil
+		}
+
+		// Check for a valid mdns ip mode
+		if config.MDNS.DisableIPv4 && config.MDNS.DisableIPv6 {
+			c.Ui.Error("Invalid mDNS configuration: both IPv4 and IPv6 are disabled")
+			return nil
+		}
+	}
+
 	// Backward compatibility hack for 'Role'
 	if config.Role != "" {
 		c.Ui.Output("Deprecation warning: 'Role' has been replaced with 'Tags'")
@@ -432,10 +453,12 @@ func (c *Command) startAgent(config *Config, agent *Agent,
 		local := agent.Serf().Memberlist().LocalNode()
 
 		// Get the bind interface if any
-		iface, _ := config.NetworkInterface()
+		iface, _ := config.MDNSNetworkInterface()
+
+		c.logger.Printf("[INFO] agent: Starting mDNS listener on interface %s", iface.Name)
 
 		_, err := NewAgentMDNS(agent, logOutput, config.ReplayOnJoin,
-			config.NodeName, config.Discover, iface, local.Addr, int(local.Port))
+			config.NodeName, config.Discover, iface, local.Addr, int(local.Port), config.MDNS)
 		if err != nil {
 			c.Ui.Error(fmt.Sprintf("Error starting mDNS listener: %s", err))
 			return nil
@@ -734,7 +757,12 @@ Options:
                            -bind if the interface is known but not the address.
                            If both are provided, then Serf verifies that the
                            interface has the bind address that is provided. This
-                           flag also sets the multicast device used for -discover.
+                           flag also sets the multicast device used for -discover,
+                           if mdns-iface is not specified.
+  -mdns-iface              Network interface to use for mDNS. If not provided, the
+                           -iface value is used.
+  -mdns-disable-ipv4       Disable IPv4 for mDNS.
+  -mdns-disable-ipv6       Disable IPv6 for mDNS.
   -advertise=0.0.0.0       Address to advertise to the other cluster members
   -config-file=foo         Path to a JSON file to read configuration from.
                            This can be specified multiple times.

cmd/serf/command/agent/config.go

@@ -45,6 +45,14 @@ func DefaultConfig() *Config {
 
 type dirEnts []os.FileInfo
 
+type MDNSConfig struct {
+	// Interface is used to provide a binding interface to use for mDNS.
+	// if not set, iface will be used.
+	Interface   string `mapstructure:"interface"`
+	DisableIPv4 bool   `mapstructure:"disable_ipv4"`
+	DisableIPv6 bool   `mapstructure:"disable_ipv6"`
+}
+
 // Config is the configuration that can be set for an Agent. Some of these
 // configurations are exposed as command-line flags to `serf agent`, whereas
 // many of the more advanced configurations can only be set by creating
@@ -154,10 +162,12 @@ type Config struct {
 	// allows Serf agents to join each other with zero configuration.
 	Discover string `mapstructure:"discover"`
 
+	MDNS MDNSConfig `mapstructure:"mdns"`
+
 	// Interface is used to provide a binding interface to use. It can be
 	// used instead of providing a bind address, as Serf will discover the
 	// address of the provided interface. It is also used to set the multicast
-	// device used with `-discover`.
+	// device used with `-discover`, if `mdns-iface` is not set
 	Interface string `mapstructure:"interface"`
 
 	// ReconnectIntervalRaw is the string reconnect interval time. This interval
@@ -292,6 +302,16 @@ func (c *Config) NetworkInterface() (*net.Interface, error) {
 	return net.InterfaceByName(c.Interface)
 }
 
+func (c *Config) MDNSNetworkInterface() (*net.Interface, error) {
+	if c.MDNS.Interface == "" && c.Interface == "" {
+		return nil, nil
+	} else if c.MDNS.Interface != "" {
+		return net.InterfaceByName(c.MDNS.Interface)
+	} else {
+		return net.InterfaceByName(c.Interface)
+	}
+}
+
 // DecodeConfig reads the configuration from the given reader in JSON
 // format and decodes it into a proper Config structure.
 func DecodeConfig(r io.Reader) (*Config, error) {
@@ -436,6 +456,19 @@ func MergeConfig(a, b *Config) *Config {
 	if b.Interface != "" {
 		result.Interface = b.Interface
 	}
+
+	if b.MDNS.Interface != "" {
+		result.MDNS.Interface = b.MDNS.Interface
+	}
+
+	if b.MDNS.DisableIPv4 == true {
+		result.MDNS.DisableIPv4 = true
+	}
+
+	if b.MDNS.DisableIPv6 == true {
+		result.MDNS.DisableIPv6 = true
+	}
+
 	if b.ReconnectInterval != 0 {
 		result.ReconnectInterval = b.ReconnectInterval
 	}

cmd/serf/command/agent/mdns.go

@@ -21,18 +21,21 @@ const (
 // AgentMDNS is used to advertise ourself using mDNS and to
 // attempt to join peers periodically using mDNS queries.
 type AgentMDNS struct {
-	agent    *Agent
-	discover string
-	logger   *log.Logger
-	seen     map[string]struct{}
-	server   *mdns.Server
-	replay   bool
-	iface    *net.Interface
+	agent       *Agent
+	discover    string
+	logger      *log.Logger
+	seen        map[string]struct{}
+	server      *mdns.Server
+	replay      bool
+	iface       *net.Interface
+	ipModes     []string
+	disableIPv4 bool
+	disableIPv6 bool
 }
 
 // NewAgentMDNS is used to create a new AgentMDNS
 func NewAgentMDNS(agent *Agent, logOutput io.Writer, replay bool,
-	node, discover string, iface *net.Interface, bind net.IP, port int) (*AgentMDNS, error) {
+	node, discover string, iface *net.Interface, bind net.IP, port int, MDNSConfig MDNSConfig) (*AgentMDNS, error) {
 	// Create the service
 	service, err := mdns.NewMDNSService(
 		node,
@@ -60,13 +63,15 @@ func NewAgentMDNS(agent *Agent, logOutput io.Writer, replay bool,
 
 	// Initialize the AgentMDNS
 	m := &AgentMDNS{
-		agent:    agent,
-		discover: discover,
-		logger:   log.New(logOutput, "", log.LstdFlags),
-		seen:     make(map[string]struct{}),
-		server:   server,
-		replay:   replay,
-		iface:    iface,
+		agent:       agent,
+		discover:    discover,
+		logger:      log.New(logOutput, "", log.LstdFlags),
+		seen:        make(map[string]struct{}),
+		server:      server,
+		replay:      replay,
+		iface:       iface,
+		disableIPv4: MDNSConfig.DisableIPv4,
+		disableIPv6: MDNSConfig.DisableIPv6,
 	}
 
 	// Start the background workers
@@ -123,9 +128,11 @@ func (m *AgentMDNS) run() {
 // poll is invoked periodically to check for new hosts
 func (m *AgentMDNS) poll(hosts chan *mdns.ServiceEntry) {
 	params := mdns.QueryParam{
-		Service:   mdnsName(m.discover),
-		Interface: m.iface,
-		Entries:   hosts,
+		Service:     mdnsName(m.discover),
+		Interface:   m.iface,
+		Entries:     hosts,
+		DisableIPv4: m.disableIPv4,
+		DisableIPv6: m.disableIPv6,
 	}
 	if err := mdns.Query(&params); err != nil {
 		m.logger.Printf("[ERR] agent.mdns: Failed to poll for new hosts: %v", err)

go.mod

@@ -8,7 +8,7 @@ require (
 	github.com/hashicorp/go-msgpack/v2 v2.1.2
 	github.com/hashicorp/go-syslog v1.0.0
 	github.com/hashicorp/logutils v1.0.0
-	github.com/hashicorp/mdns v1.0.4
+	github.com/hashicorp/mdns v1.0.5
 	github.com/hashicorp/memberlist v0.5.1
 	github.com/mitchellh/cli v1.1.5
 	github.com/mitchellh/mapstructure v1.5.0

go.sum

@@ -72,8 +72,8 @@ github.com/hashicorp/golang-lru v1.0.2 h1:dV3g9Z/unq5DpblPpw+Oqcv4dU/1omnb4Ok8iP
 github.com/hashicorp/golang-lru v1.0.2/go.mod h1:iADmTwqILo4mZ8BN3D2Q6+9jd8WM5uGBxy+E8yxSoD4=
 github.com/hashicorp/logutils v1.0.0 h1:dLEQVugN8vlakKOUE3ihGLTZJRB4j+M2cdTm/ORI65Y=
 github.com/hashicorp/logutils v1.0.0/go.mod h1:QIAnNjmIWmVIIkWDTG1z5v++HQmx9WQRO+LraFDTW64=
-github.com/hashicorp/mdns v1.0.4 h1:sY0CMhFmjIPDMlTB+HfymFHCaYLhgifZ0QhjaYKD/UQ=
-github.com/hashicorp/mdns v1.0.4/go.mod h1:mtBihi+LeNXGtG8L9dX59gAEa12BDtBQSp4v/YAJqrc=
+github.com/hashicorp/mdns v1.0.5 h1:1M5hW1cunYeoXOqHwEb/GBDDHAFo0Yqb/uz/beC6LbE=
+github.com/hashicorp/mdns v1.0.5/go.mod h1:mtBihi+LeNXGtG8L9dX59gAEa12BDtBQSp4v/YAJqrc=
 github.com/hashicorp/memberlist v0.5.1 h1:mk5dRuzeDNis2bi6LLoQIXfMH7JQvAzt3mQD0vNZZUo=
 github.com/hashicorp/memberlist v0.5.1/go.mod h1:zGDXV6AqbDTKTM6yxW0I4+JtFzZAJVoIPvss4hV8F24=
 github.com/huandu/xstrings v1.3.1/go.mod h1:y5/lhBue+AyNmUVz9RLU9xbLR0o4KIIExikq4ovT0aE=