Fix: Add a way to differentiate between bind and local address

Signed-off-by: Knut Ahlers <knut@ahlers.me>

README.md

@@ -63,28 +63,34 @@ healthCheck:
     path: /healthz
     tls: true
 
-# Local Address and Port describes the IP and Port to bind the service
-# to. The Address given is used for the SNAT and therefore should for
-# example be the public IP of the machine
-localAddr: 203.0.113.1
-localPort: 443
+# Bind Address and Port describes the IP and Port to bind the service
+# to.
+bindAddr: 203.0.113.1
+bindPort: 443
+
+# Proto describes which protocol should be routed (defaults to tcp)
+proto: tcp
 
 # Targets is a list of routing targets which are checked for their
 # liveness status and if they are live, they are included in the NAT
 # rulesets.
-# Each target consists of an Address, a Port and a Weight. The weight
+# Each target consists of two Addresses, a Port and a Weight. The weight
 # is defined as an integer and increases / decreases the percentage
 # of the traffic that specific target will receive. (For example
 # setting all weights to 1 will distribute the traffic equally between
 # them, setting one to 2 will double the traffic to that target.)
+# The localAddr is used for the SNAT to map the source IP.
 targets:
   - addr: 10.1.2.4
+    localAddr: 10.1.2.1
     port: 443
     weight: 1
   - addr: 10.1.2.5
+    localAddr: 10.1.2.1
     port: 443
     weight: 1
   - addr: 10.1.2.6
+    localAddr: 10.1.2.1
     port: 443
     weight: 1
 ```

pkg/config/config.go

@@ -23,9 +23,9 @@ type (
 	Service struct {
 		Name        string             `yaml:"name"`
 		HealthCheck ServiceHealthCheck `yaml:"healthCheck"`
-		LocalAddr   string             `yaml:"localAddr"`
-		LocalPort   int                `yaml:"localPort"`
-		LocalProto  string             `yaml:"localProto"`
+		BindAddr    string             `yaml:"bindAddr"`
+		BindPort    int                `yaml:"bindPort"`
+		Proto       string             `yaml:"proto"`
 		Targets     []Target           `yaml:"targets"`
 	}
 
@@ -40,9 +40,10 @@ type (
 	// Target represents a load-balancing target to route the traffic
 	// to in case it is deemed alive
 	Target struct {
-		Addr   string `yaml:"addr"`
-		Port   int    `yaml:"port"`
-		Weight int    `yaml:"weight"`
+		Addr      string `yaml:"addr"`
+		LocalAddr string `yaml:"localAddr"`
+		Port      int    `yaml:"port"`
+		Weight    int    `yaml:"weight"`
 	}
 )
 
@@ -73,12 +74,12 @@ func Load(fn string) (cf File, err error) {
 	return cf, nil
 }
 
-// Proto evaluates the LocalProto and returns tcp if empty
-func (s Service) Proto() string {
-	if s.LocalProto == "" {
+// Protocol evaluates the Proto and returns tcp if empty
+func (s Service) Protocol() string {
+	if s.Proto == "" {
 		return "tcp"
 	}
-	return s.LocalProto
+	return s.Proto
 }
 
 func (t Target) String() string { return fmt.Sprintf("%s:%d", t.Addr, t.Port) }

pkg/iptables/iptables.go

@@ -34,8 +34,9 @@ type (
 	// with random distribution and given probability
 	NATTarget struct {
 		Addr      string
+		BindAddr  string
+		BindPort  int
 		LocalAddr string
-		LocalPort int
 		Port      int
 		Proto     string
 		Weight    float64
@@ -182,8 +183,8 @@ func (c *Client) buildServiceTable(service string, cType chainType) (rules [][]s
 				"--probability", strconv.FormatFloat(nt.Weight/weightLeft, 'f', probPrecision, probBitsize),
 
 				"-p", nt.Proto,
-				"-d", nt.LocalAddr,
-				"--dport", strconv.Itoa(nt.LocalPort),
+				"-d", nt.BindAddr,
+				"--dport", strconv.Itoa(nt.BindPort),
 
 				"-j", "DNAT",
 				"--to-destination", fmt.Sprintf("%s:%d", nt.Addr, nt.Port),

pkg/servicemonitor/monitor.go

@@ -67,11 +67,12 @@ func (m Monitor) updateRoutingTargets(checker healthcheck.Checker) (err error) {
 
 			tgt := iptables.NATTarget{
 				Addr:      t.Addr,
-				LocalAddr: m.svc.LocalAddr,
-				LocalPort: m.svc.LocalPort,
+				BindAddr:  m.svc.BindAddr,
+				BindPort:  m.svc.BindPort,
+				LocalAddr: t.LocalAddr,
 				Port:      t.Port,
 				Weight:    float64(t.Weight),
-				Proto:     m.svc.Proto(),
+				Proto:     m.svc.Protocol(),
 			}
 
 			if err := checker.Check(m.svc.HealthCheck.Settings, t); err != nil {