Generic dnsmasq on Alpine image

Sometimes we need to quickly override DNS entries for testing purposes. dnsmasq provides an easy way to override a few DNS records, while still (recursively) resolving any other records.

This container is just Alpine Linux with dnsmasq installed.

Using the Pre-built Image

% docker pull suet/dnsmasq

Building the Image

% git clone https://github.com/su-et/dnsmasq.git
% cd dnsmasq
% docker build -t dnsmasq .

Running

You can either mount a hosts file:

% docker run -v hosts:/etc/hosts.dnsmasq dnsmasq:alpine

or, if you only need a single record, you can pass a host record on the command line:

% docker run dnsmasq:alpine --host-record=www.example.org,example.org,127.0.0.1,60

The --host-record syntax is hostname,ipv4,ipv6,ttl. Multiple hostnames can be specified (separated by commas); ipv4, ipv6, and ttl are all optional, although if no address is specified, the "real" record will be used (if it exists). If either, or both, addresses are specified without ttl, a TTL of 0 will be returned.

Examples:

Without any overrides

% dig +noall +answer @172.17.0.3 example.org
example.org.		4479	IN	A	93.184.216.34

% dig +noall +answer @172.17.0.3 example.org aaaa
example.org.		4481	IN	AAAA	2606:2800:220:1:248:1893:25c8:1946

Replace the IPv6 address and TTL

Replace only the IPv6 address of example.org

docker run dnsmasq:alpine --host-record=example.org,::1,60

% dig +noall +answer @172.17.0.3 example.org
example.org.		4502	IN	A	93.184.216.34
% dig +noall +answer @172.17.0.3 example.org aaaa
example.org.		60	IN	AAAA	::1

Replace the IPv4 address and TTL

Replace only the IPv4 address of example.org

docker run dnsmasq:alpine --host-record=example.org,127.0.0.1,60

% dig +noall +answer @172.17.0.3 example.org
example.org.		60	IN	A	127.0.0.1
% dig +noall +answer @172.17.0.3 example.org aaaa
example.org.		4502	IN	AAAA	2606:2800:220:1:248:1893:25c8:1946

Replace both addresses and TTL

docker run dnsmasq:alpine --host-record=example.org,127.0.0.1,::1,60

% dig +noall +answer @172.17.0.3 example.org
example.org.		60	IN	A	127.0.0.1
% dig +noall +answer @172.17.0.3 example.org aaaa
example.org.		60	IN	AAAA	::1