weavedns

README

Weave DNS server

The Weave DNS server answers name queries in a Weave network. It is run per-host, to be supplied as the nameserver for containers on that host. It is then told about hostnames for the local containers. For other names it will ask the other weave hosts, or fall back to using the host's configured name server.

Use

The Weave DNS container should be started after the Weave router -- i.e., after running weave launch -- and joined to the Weave network.

In general, it should be given an IP in the same subnet as the router. To watch for container events it must have the docker socker mounted.

$ weave launch 10.0.0.1/16
$ weave run 10.0.0.2/16 --name=weavedns -v /var/run/docker.sock:/var/run/docker.sock zettio/weavedns

The docker IP for the container can then be provided as the --dns value for other containers:

$ dns_ip=$(docker inspect --format='{{ .NetworkSettings.IPAddress }}' weavedns)
$ shell1=$(weave run 10.0.1.2/24 -h shell.weave.local --dns=$dns_ip -t ubuntu /bin/bash)

To associate a hostname with an IP, use an HTTP PUT to the DNS server:

$ shell1_ip=$(docker inspect --format='{{ .NetworkSettings.IPAddress }}' $shell1)
$ curl -X PUT "http://$dns_ip:6785/name/$shell1/10.0.1.2?fqdn=shell1.weave.local&routing_prefix=24&local_ip=$shell1_ip"

You should now be able to look up the name:

$ dig @$dns_ip +short shell1.weave.local

By default, the server will also watch docker events and remove entries for any containers that die. You can tell it not to by adding --watch=false to the container args:

$ weave run 10.0.0.2/16 --name=weavedns -v /var/run/docker.sock:/var/run/docker.sock zettio/weavedns --watch=false

Present limitations

• The server will not know about restarted containers, unless you re-PUT the name.
• The server will forget names if it is itself restarted.
• The server may give unreachable IPs as answers, since it doesn't try to filter by subnet yet.
• We use UDP broadcast to find out about remote names (from Weave DNS servers on other hosts); this likely won't scale well beyond a certain point T.B.D., so we'll have to come up with another scheme.