Merge pull request #1135 from weaveworks/issues/1028-weave-dns-lookup

Implement `weave dns-lookup`

Closes #1028.

prog/weaveexec/Dockerfile

@@ -9,6 +9,7 @@ RUN apk add --update \
     iproute2 \
     util-linux \
     conntrack-tools \
+    bind-tools \
   && rm -rf /var/cache/apk/*
 
 WORKDIR /home/weave

site/features.md

@@ -296,13 +296,9 @@ returned. So now
     host2$ ping 10.2.1.132
 
 will work, and, more interestingly, we can ping our `a1` application
-container, which is residing on `$HOST1`, after finding its IP
-address:
+container, which is residing on `$HOST1`:
 
-    host1$ weave ps a1
-    a1 1e:88:d7:5b:77:68 10.2.1.2/24
-
-    host2$ ping 10.2.1.2
+    host2$ ping $(weave dns-lookup a1)
 
 Multiple subnet addresses can be exposed or hidden with a single
 invocation:
@@ -337,11 +333,8 @@ explained [above](#host-network-integration), i.e.
 Then we add a NAT rule to route from the outside world to the
 destination container service.
 
-    host1$ weave ps a1
-    a1 1e:88:d7:5b:77:68 10.2.1.2/24
-
     host2$ iptables -t nat -A PREROUTING -p tcp -i eth0 --dport 2211 \
-           -j DNAT --to-destination 10.2.1.2:4422
+           -j DNAT --to-destination $(weave dns-lookup a1):4422
 
 Here we are assuming that the "outside world" is connecting to `$HOST2`
 via 'eth0'. We want TCP traffic to port 2211 on the external IPs to be

site/weavedns.md

@@ -16,6 +16,7 @@ hosts.
 * [Load balancing](#load-balancing)
 * [Fault resilience](#fault-resilience)
 * [Adding and removing extra DNS entries](#add-remove)
+* [Resolve weaveDNS entries from host](#resolve-weavedns-entries-from-host)
 * [Hot-swapping service containers](#hot-swapping)
 * [Retaining DNS entries when containers stop](#retain-stopped)
 * [Configuring a custom TTL](#ttl)
@@ -133,7 +134,6 @@ one of the `pingme` containers and re-run the ping tests, eventually
 [cache expiry time](#ttl)) we will only be hitting the address of the
 container that is still alive.
 
-
 ## <a name="add-remove"></a>Adding and removing extra DNS entries
 
 If you want to give the container a name in DNS *other* than its
@@ -157,6 +157,14 @@ $ weave dns-remove 10.2.1.27 $C
 When queried about a name with multiple IPs, weaveDNS returns all IPs
 available in a random order.
 
+## <a name="resolve-weavedns-entries-from-host"></a>Resolve weaveDNS entries from host
+
+You can resolve entries from any host running weaveDNS with `weave
+dns-lookup`:
+
+    host1$ weave dns-lookup pingme
+    10.40.0.1
+
 ## <a name="hot-swapping"></a>Hot-swapping service containers
 
 If you would like to deploy a new version of a service, keep the old

test/250_dns_lookup_test.sh

@@ -0,0 +1,16 @@
+#! /bin/bash
+
+. ./config.sh
+
+C1=10.2.0.78
+
+start_suite "Cross host dns-lookup"
+
+weave_on $HOST1 launch
+weave_on $HOST2 launch $HOST1
+
+start_container $HOST1 $C1/24 --name c1
+
+assert "weave_on $HOST2 dns-lookup c1" $C1
+
+end_suite

weave

@@ -47,6 +47,7 @@ weave attach        [<addr> ...] <container_id>
 weave detach        [<addr> ...] <container_id>
 weave dns-add       <ip_address> [<ip_address> ...] <container_id> [-h <fqdn>]
 weave dns-remove    <ip_address> [<ip_address> ...] <container_id> [-h <fqdn>]
+weave dns-lookup    <unqualified_name>
 weave expose        [<addr> ...] [-h <fqdn>]
 weave hide          [<addr> ...]
 weave ps            [<container_id> ...]
@@ -1334,6 +1335,11 @@ case "$COMMAND" in
             delete_dns_fqdn $CONTAINER "$3" $IP_ARGS
         fi
         ;;
+    dns-lookup)
+        [ $# -eq 1 ] || usage
+        docker_bridge_ip
+        dig @$DOCKER_BRIDGE_IP +short $1
+        ;;
     expose)
         collect_cidr_args "$@"
         shift $CIDR_ARG_COUNT