docker-dns

Automatic container DNS for Docker in a single Python file.

Note that docker-dns-rest expands on this, adding a REST API to add and remove domain names dynamically, allowing multiple domain names to be associated with containers, either by name or container ID. It also includes support for wildcards.

Usage

Run some containers:

% docker run -d --name foo ubuntu bash -c "sleep 600"

Start up dockerdns:

% docker run -d --name dns -v /var/run/docker.sock:/docker.sock phensley/docker-dns \
    --domain example.com

If your Docker instance uses TLS:

% docker run --name dns -e DOCKER_HOST=https://<host>:<port> --rm phensley/docker-dns --domain example.com

Start more containers:

% docker run -d --name bar ubuntu bash -c "sleep 600"

Check dockerdns logs:

% docker logs dns
2014-10-08T20:45:37.349161 [dockerdns] table.add dns.example.com -> 172.17.0.3
2014-10-08T20:45:37.351574 [dockerdns] table.add foo.example.com -> 172.17.0.2
2014-10-08T20:45:37.351574 [dockerdns] table.add bar.example.com -> 172.17.0.4

Query for the containers by hostname:

% host foo.example.com 172.17.0.3
Using domain server:
Name: 172.17.0.3
Address: 172.17.0.3#53
Aliases:

foo.example.com has address 172.17.0.2

Query by IP address:

% host 172.17.0.2 172.17.0.3
Using domain server:
Name: 172.17.0.3
Address: 172.17.0.3#53
Aliases:

2.0.17.172.in-addr.arpa domain name pointer bar.example.com.
2.0.17.172.in-addr.arpa domain name pointer 5046e96685a2.example.com.

Use dns container as a resolver inside a container:

% docker run -it --dns $(docker inspect -f '{{.NetworkSettings.IPAddress}}' dns) \
    --dns-search example.com ubuntu bash

💡 Tip：As we don't add -d option, we will login this docker container. And the following steps are done in this docker container.

root@95840788bf08:/# cat /etc/resolv.conf
nameserver 172.17.0.3
search example.com

root@95840788bf08:/# ping foo
PING foo.example.com (172.17.0.2) 56(84) bytes of data.
64 bytes from 172.17.0.2: icmp_seq=1 ttl=64 time=0.112 ms
64 bytes from 172.17.0.2: icmp_seq=2 ttl=64 time=0.112 ms

Names not rooted in example.com will be resolved recursively using Google's resolver 8.8.8.8 by default:

root@95840788bf08:/# ping github.com
PING github.com (192.30.252.128) 56(84) bytes of data.
64 bytes from 192.30.252.128: icmp_seq=1 ttl=61 time=21.3 ms

To disable recursive resolution, use the --no-recursion flag:

% docker run --name dns -v /var/run/docker.sock:/docker.sock phensley/docker-dns \
    --domain example.com --no-recursion

Now names not rooted in example.com will fail to resolve:

% docker run -it --dns $(docker inspect -f '{{.NetworkSettings.IPAddress}}' dns) \
    --dns-search example.com ubuntu bash
root@4d15342387b0:/# ping github.com
ping: unknown host github.com

Pointing a subdomain to some IP

% docker run --name dns -v /var/run/docker.sock:/docker.sock phensley/docker-dns \
    --domain example.com --record localhost:127.0.0.1

# This will cause localhost.example.com to resolve to 127.0.0.1

Pointing all subdomains to some IP

% docker run --name dns -v /var/run/docker.sock:/docker.sock phensley/docker-dns \
    --domain example.com --record *:172.18.0.4

# This makes everything not explicitly set as a subdomain to resolve to 172.18.0.4.
# Useful when your reverse proxy is there.

You can also blacklist specific networks (space-separated) from the resolution table:

% docker run --name dns -v /var/run/docker.sock:/docker.sock \
    -e NETWORK_BLACKLIST="172.18.0.0/16 172.19.0.0/16" phensley/docker-dns \
    --domain example.com

# Useful when your network topology or firewall prevents clients from accessing some addresses.

License

Copyright (c) 2014 Patrick Hensley

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.