Fetch DNS listen address from daemon

instead of assuming it's on the Docker bridge

Also move DNS address validation into NewDNSServer(),
so we only do it once.

nameserver/dns.go

@@ -90,7 +90,7 @@ type DNSServer struct {
 	ns      *Nameserver
 	domain  string
 	ttl     uint32
-	address string
+	address string // listen address and port, e.g. 1.2.3.4:53
 
 	servers   []*dns.Server
 	upstream  Upstream
@@ -99,6 +99,10 @@ type DNSServer struct {
 }
 
 func NewDNSServer(ns *Nameserver, domain, address string, upstream Upstream, ttl uint32, clientTimeout time.Duration) (*DNSServer, error) {
+	if _, _, err := net.SplitHostPort(address); err != nil {
+		return nil, fmt.Errorf("invalid DNS listen address %q: %v", address, err)
+	}
+
 	s := &DNSServer{
 		ns:        ns,
 		domain:    dns.Fqdn(domain),

nameserver/http.go

@@ -3,6 +3,7 @@ package nameserver
 import (
 	"encoding/json"
 	"fmt"
+	"net"
 	"net/http"
 
 	"github.com/gorilla/mux"
@@ -84,3 +85,13 @@ func (n *Nameserver) HandleHTTP(router *mux.Router, dockerCli *docker.Client) {
 		}
 	})
 }
+
+func (d *DNSServer) HandleHTTP(router *mux.Router) {
+	router.Methods("GET").Path("/dns-address-port").HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, d.address)
+	})
+	router.Methods("GET").Path("/dns-address").HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		host, _, _ := net.SplitHostPort(d.address) // address is validated in NewDNSServer()
+		fmt.Fprint(w, host)
+	})
+}

prog/weaver/main.go

@@ -55,10 +55,7 @@ type dnsConfig struct {
 
 // return the address part of the DNS listen address, without ":53" on the end
 func (c dnsConfig) addressOnly() string {
-	addr, _, err := net.SplitHostPort(c.ListenAddress)
-	if err != nil {
-		Log.Fatalf("Error when parsing DNS listen address %q: %s", c.ListenAddress, err)
-	}
+	addr, _, _ := net.SplitHostPort(c.ListenAddress)
 	return addr
 }
 
@@ -474,6 +471,7 @@ func main() {
 		}
 		if ns != nil {
 			ns.HandleHTTP(muxRouter, dockerCli)
+			dnsserver.HandleHTTP(muxRouter)
 		}
 		router.HandleHTTP(muxRouter)
 		HandleHTTP(muxRouter, version, router, allocator, defaultSubnet, ns, dnsserver, proxy, plugin, &waitReady)

site/tasks/weavedns/weavedns.md

@@ -39,6 +39,10 @@ the same time, the hostname takes precedence. In this circumstance, if
 the hostname is not in the weaveDNS domain, the container is *not*
 registered, but it will still use weaveDNS for resolution.
 
+By default, weaveDNS will listen on port 53 on the address of the
+Docker bridge. To make it listen on a different address or port use
+`weave launch --dns-listen-address <address>:<port>`
+
 To disable an application container's use of weaveDNS, add the
 `--without-dns` option to `weave launch`. To
 disable weaveDNS itself, launch weave with the `--no-dns` option.

weave

@@ -43,6 +43,7 @@ weave launch        [--password <pass>] [--trusted-subnets <cidr>,...]
                     [--host <ip_address>]
                     [--name <mac>] [--nickname <nickname>]
                     [--no-restart] [--resume] [--no-discovery] [--no-dns]
+                    [--dns-listen-address <address>:<port>]
                     [--ipalloc-init <mode>]
                     [--ipalloc-range <cidr> [--ipalloc-default-subnet <cidr>]]
                     [--plugin=false] [--proxy=false]
@@ -775,6 +776,7 @@ dns_args() {
     DNS_DOMAIN=${DNS_DOMAIN:-$(call_weave GET /domain 2>/dev/null)} || retval=$?
     [ "$retval" -eq 4 ] && return 0
     DNS_DOMAIN=${DNS_DOMAIN:-weave.local.}
+    DNS_ADDRESS=${DNS_ADDRESS:-$(call_weave GET /dns-address 2>/dev/null)}
 
     NAME_ARG=""
     HOSTNAME_SPECIFIED=
@@ -803,8 +805,7 @@ dns_args() {
     done
     [ -n "$WITHOUT_DNS" ] && return 0
 
-    [ -n "$DOCKER_BRIDGE_IP" ] || DOCKER_BRIDGE_IP=$(util_op bridge-ip $DOCKER_BRIDGE)
-    DNS_ARGS="--dns=$DOCKER_BRIDGE_IP"
+    DNS_ARGS="--dns=$DNS_ADDRESS"
     if [ -n "$NAME_ARG" -a -z "$HOSTNAME_SPECIFIED" ] ; then
         HOSTNAME="$NAME_ARG.${DNS_DOMAIN%.}"
         if [ ${#HOSTNAME} -gt 64 ] ; then
@@ -1489,8 +1490,8 @@ case "$COMMAND" in
         ;;
     dns-lookup)
         [ $# -eq 1 ] || usage
-        DOCKER_BRIDGE_IP=$(util_op bridge-ip $DOCKER_BRIDGE)
-        dig @$DOCKER_BRIDGE_IP +short $1
+        DNS_ADDRESS=${DNS_ADDRESS:-$(call_weave GET /dns-address-port 2>/dev/null)}
+        dig @${DNS_ADDRESS%:*} -p ${DNS_ADDRESS#*:} +short $1
         ;;
     expose)
         WITHOUT_MASQUERADE=