Implement `translate_wan_addrs` config option

This knob tells consul whether it should prefer the WAN address (if set)
when making service lookups in remote datacenters. This enables
reachability for remote services which are behind a NAT.

command/agent/config.go

@@ -189,6 +189,10 @@ type Config struct {
 	// Serf WAN IP. If not specified, the general advertise address is used.
 	AdvertiseAddrWan string `mapstructure:"advertise_addr_wan"`
 
+	// TranslateWanAddrs controls whether or not Consul should prefer
+	// the AdvertiseAddrWan address when doing lookups in remote datacenters.
+	TranslateWanAddrs bool `mapstructure:"translate_wan_addrs"`
+
 	// Port configurations
 	Ports PortConfig
 
@@ -968,6 +972,9 @@ func MergeConfig(a, b *Config) *Config {
 	if b.AdvertiseAddrWan != "" {
 		result.AdvertiseAddrWan = b.AdvertiseAddrWan
 	}
+	if b.TranslateWanAddrs == true {
+		result.TranslateWanAddrs = true
+	}
 	if b.AdvertiseAddrs.SerfLan != nil {
 		result.AdvertiseAddrs.SerfLan = b.AdvertiseAddrs.SerfLan
 		result.AdvertiseAddrs.SerfLanRaw = b.AdvertiseAddrs.SerfLanRaw

command/agent/dns.go

@@ -524,9 +524,15 @@ RPC:
 	// Perform a random shuffle
 	out.Nodes.Shuffle()
 
+	// Determine whether we should use the WAN address or not
+	var useWan bool
+	if d.agent.config.TranslateWanAddrs && datacenter != d.agent.config.Datacenter {
+		useWan = true
+	}
+
 	// Add various responses depending on the request
 	qType := req.Question[0].Qtype
-	d.serviceNodeRecords(out.Nodes, req, resp, ttl)
+	d.serviceNodeRecords(out.Nodes, req, resp, ttl, useWan)
 
 	if qType == dns.TypeSRV {
 		d.serviceSRVRecords(datacenter, out.Nodes, req, resp, ttl)
@@ -620,9 +626,15 @@ RPC:
 		return
 	}
 
+	// Determine whether we should use the WAN address or not
+	var useWan bool
+	if d.agent.config.TranslateWanAddrs && datacenter != d.agent.config.Datacenter {
+		useWan = true
+	}
+
 	// Add various responses depending on the request.
 	qType := req.Question[0].Qtype
-	d.serviceNodeRecords(out.Nodes, req, resp, ttl)
+	d.serviceNodeRecords(out.Nodes, req, resp, ttl, useWan)
 	if qType == dns.TypeSRV {
 		d.serviceSRVRecords(datacenter, out.Nodes, req, resp, ttl)
 	}
@@ -646,18 +658,22 @@ RPC:
 }
 
 // serviceNodeRecords is used to add the node records for a service lookup
-func (d *DNSServer) serviceNodeRecords(nodes structs.CheckServiceNodes, req, resp *dns.Msg, ttl time.Duration) {
+func (d *DNSServer) serviceNodeRecords(nodes structs.CheckServiceNodes, req, resp *dns.Msg, ttl time.Duration, useWan bool) {
 	qName := req.Question[0].Name
 	qType := req.Question[0].Qtype
 	handled := make(map[string]struct{})
 	for _, node := range nodes {
-		// Avoid duplicate entries, possible if a node has
+		// Prefer the Service Address or WAN Address over the
-		// the same service on multiple ports, etc.
+		// Node Address when configured
 		addr := node.Node.Address
 		if node.Service.Address != "" {
 			addr = node.Service.Address
+		} else if useWan == true && node.Node.WanAddress != "" {
+			addr = node.Node.WanAddress
 		}
 
+		// Avoid duplicate entries, possible if a node has
+		// the same service on multiple ports, etc.
 		if _, ok := handled[addr]; ok {
 			continue
 		}

command/agent/local.go

@@ -526,7 +526,7 @@ func (l *localState) syncService(id string) error {
 		Datacenter:   l.config.Datacenter,
 		Node:         l.config.NodeName,
 		Address:      l.config.AdvertiseAddr,
-		WanAddress:   l.config.ConsulConfig.SerfWANConfig.MemberlistConfig.AdvertiseAddr,
+		WanAddress:   l.config.AdvertiseAddrWan,
 		Service:      l.services[id],
 		WriteRequest: structs.WriteRequest{Token: l.serviceToken(id)},
 	}
@@ -584,7 +584,7 @@ func (l *localState) syncCheck(id string) error {
 		Datacenter:   l.config.Datacenter,
 		Node:         l.config.NodeName,
 		Address:      l.config.AdvertiseAddr,
-		WanAddress:   l.config.ConsulConfig.SerfWANConfig.MemberlistConfig.AdvertiseAddr,
+		WanAddress:   l.config.AdvertiseAddrWan,
 		Service:      service,
 		Check:        l.checks[id],
 		WriteRequest: structs.WriteRequest{Token: l.checkToken(id)},