docker-devdns

DNS server resolving .dev domain against docker container names

Use case

Make docker containers discoverable via DNS for development environments, like when running a bunch of containers on your laptop.

This does not use any etcd/zookeeper backend or registrator process but maintains it's own container name cache

See etcd/skydns for a more complete solution.

Names, unlike skydock/progrium-registrator are short: it's $CONTAINER_NAME.dev. If a container name contains dots that will form subdomains.

Design

Listens to container creation events and maintains a name<->ip cache.

Requests for a special toplevel domain (default .dev) tries to match any running docker container with the same name.

Requests for other domains are resolved by the operating system resolver, This is so that we can cooperate with other special DNS server solutions installed in your development environment, like VPN-assigned DNS-servers, vagrant landrush DNS servers etc.

Usage

There are two cases:

1. Containers trying to resolve each other
2. Non-containers trying to resolve container names

For outside resolving, on OSX:

create a file /etc/resolver/dev:

nameserver <listen addr of docker-devdns>

outside resolving, other OS:

use a dns server which can selectively forward requests for the .dev domain to this server. For example dnsmasq.

for container-to-container resolving, add the following to your docker daemon options:

--dns <listen addr of docker-devdns> --dns-search dev

by default we listen to port 53, since this is the easiest to make containers use.

DO NOT point /etc/resolv.conf of your docker host to this server. It will cause a resolver error since we try to look up any request for other names by gethostbyname() which creates a loop. We try to detect this misconfiguration on startup.

If you only want .dev names to be resolvable, you can disable this behavior by using

-local-resolver=false

No upstream server can be configured (yet).

Flags

-docker-host="tcp://docker:2375": docker host url, or set DOCKER_HOST
-domain="dev": domain
-listen-addr=":53": Listen address for DNS
-local-resolver=true: Perform local gethostbyname queries for other domains

Performance

Listens to container creation events and maintains a local cache based on that

Limitations

We only respond properly to A and AAAA queries.