Merge pull request #13 from danlsgiga/iptables-listen-destination-port

Add listen port option for NAT routing

README.md

@@ -52,6 +52,14 @@ GoCast supports consul for automatic service discovery and healthchecking. For t
 
 If `gocast_monitor=consul` is specified, then GoCast uses the defined healthchecks in consul as the health monitors for the service.
 
+If `gocast_nat=protocol:listenPort:destinationPort` is specified, then GoCast will create NAT rules, via iptables, and map traffic destined to the assigned VIP and the specified `listenPort` to the physical IP and `destinationPort`.
+
+Example: `gocast_nat=tcp:53:8053` and `gocast_nat=udp:53:8053`
+
+Alternatively, if `gocast_nat=protocol:port` is specified, then GoCast will create NAT rules, via iptables, and map traffic destined to the assigned VIP and the specified `port` to the physical IP and `port`.
+
+Example: `gocast_nat=tcp:53` and `gocast_nat=udp:53`
+
 ## Docker support
 The docker image at mayuresh82/gocast can be used to run GoCast inside a container. In order for GoCast to manipulate the host network stack correctly, the container needs to run with NET_ADMIN capablity and host mode networking. For example:
 ```
@@ -65,7 +73,7 @@ Certain orchestration solutions such as Nomad run the docker containers with pub
 
 - Start the service container in host networking mode OR
 
-- Register NAT rules for your service with GoCast for the required protocol/port(s). GoCast will then create iptables NAT rules that map traffic destined to the assigned VIP to the physical IP address. This is achieved by adding the `nat=protocol:port` tag(s) in consul or the http query.
+- Register NAT rules for your service with GoCast for the required protocol/port(s). GoCast will then create iptables NAT rules that map traffic destined to the assigned VIP to the physical IP address. This is achieved by adding the `nat=protocol:listenPort:destinationPort` in the http query or `gocast_nat=protocol:listenPort:destinationPort` tag(s) in consul, as shown in the Consul integration section above.
 
 **Why not just use ExaBGP or something similar ?**
 

controller/monitor.go

@@ -202,12 +202,18 @@ func (m *MonitorMgr) Remove(appName string) {
 		}
 		for _, nat := range a.app.Nats {
 			parts := strings.Split(nat, ":")
-			if len(parts) != 2 {
+			switch len(parts) {
+			case 3:
+				if err := natRule("D", a.app.Vip.Net.IP, m.ctrl.localIP, parts[0], parts[1], parts[2]); err != nil {
+					glog.Errorf("Failed to remove app: %s: %v", a.app.Name, err)
+				}
+			case 2:
+				if err := natRule("D", a.app.Vip.Net.IP, m.ctrl.localIP, parts[0], parts[1], parts[1]); err != nil {
+					glog.Errorf("Failed to remove app: %s: %v", a.app.Name, err)
+				}
+			default:
 				continue
 			}
-			if err := natRule("D", a.app.Vip.Net.IP, m.ctrl.localIP, parts[0], parts[1]); err != nil {
-				glog.Errorf("Failed to remove app: %s: %v", a.app.Name, err)
-			}
 		}
 	}
 	delete(m.monitors, appName)
@@ -248,12 +254,18 @@ func (m *MonitorMgr) checkCond(am *appMon) error {
 			}
 			for _, nat := range app.Nats {
 				parts := strings.Split(nat, ":")
-				if len(parts) != 2 {
+				switch len(parts) {
+				case 3:
+					if err := natRule("A", app.Vip.Net.IP, m.ctrl.localIP, parts[0], parts[1], parts[2]); err != nil {
+						return err
+					}
+				case 2:
+					if err := natRule("A", app.Vip.Net.IP, m.ctrl.localIP, parts[0], parts[1], parts[1]); err != nil {
+						return err
+					}
+				default:
 					continue
 				}
-				if err := natRule("A", app.Vip.Net.IP, m.ctrl.localIP, parts[0], parts[1]); err != nil {
-					return err
-				}
 			}
 			if err := m.ctrl.Announce(app.Vip); err != nil {
 				return fmt.Errorf("Failed to announce route: %v", err)
@@ -315,10 +327,14 @@ func (m *MonitorMgr) CloseAll() {
 		deleteLoopback(am.app.Vip.Net)
 		for _, nat := range am.app.Nats {
 			parts := strings.Split(nat, ":")
-			if len(parts) != 2 {
+			switch len(parts) {
+			case 3:
+				natRule("D", am.app.Vip.Net.IP, m.ctrl.localIP, parts[0], parts[1], parts[2])
+			case 2:
+				natRule("D", am.app.Vip.Net.IP, m.ctrl.localIP, parts[0], parts[1], parts[1])
+			default:
 				continue
 			}
-			natRule("D", am.app.Vip.Net.IP, m.ctrl.localIP, parts[0], parts[1])
 		}
 	}
 }

controller/system.go

@@ -86,10 +86,10 @@ func deleteLoopback(addr *net.IPNet) error {
 	return nil
 }
 
-func natRule(op string, vip, localAddr net.IP, protocol, port string) error {
+func natRule(op string, vip, localAddr net.IP, protocol, lport, dport string) error {
 	cmd := fmt.Sprintf(
 		"iptables -t nat -%s PREROUTING -p %s -d %s --dport %s -j DNAT --to-destination %s:%s",
-		op, protocol, vip.String(), port, localAddr.String(), port,
+		op, protocol, vip.String(), lport, localAddr.String(), dport,
 	)
 	cmdList := getCmdList(cmd)
 	_, err := exec.Command(execCmd, cmdList...).Output()