Dockerize an apt-cacher-ng service

Estimated reading time: 4 minutes

Note:

• If you don’t like sudo then see Giving non-root access.
• If you’re using macOS or docker via TCP then you shouldn’t use sudo.

When you have multiple Docker servers, or build unrelated Docker containers which can’t make use of the Docker build cache, it can be useful to have a caching proxy for your packages. This container makes the second download of any package almost instant.

Use the following Dockerfile:

# syntax=docker/dockerfile:1

# Build: docker build -t apt-cacher .
# Run: docker run -d -p 3142:3142 --name apt-cacher-run apt-cacher
#
# and then you can run containers with:
#   docker run -t -i --rm -e http_proxy http://dockerhost:3142/ debian bash
#
# Here, `dockerhost` is the IP address or FQDN of a host running the Docker daemon
# which acts as an APT proxy server.
FROM   ubuntu

VOLUME ["/var/cache/apt-cacher-ng"]
RUN    apt-get update && apt-get install -y apt-cacher-ng

EXPOSE 3142
CMD    chmod 777 /var/cache/apt-cacher-ng && /etc/init.d/apt-cacher-ng start && tail -f /var/log/apt-cacher-ng/*

To build the image using:

$ docker build -t eg_apt_cacher_ng .

Then run it, mapping the exposed port to one on the host

$ docker run -d -p 3142:3142 --name test_apt_cacher_ng eg_apt_cacher_ng

To see the logfiles that are tailed in the default command, you can use:

$ docker logs -f test_apt_cacher_ng

To get your Debian-based containers to use the proxy, you have following options. Replace dockerhost with the IP address or FQDN of the host running the test_apt_cacher_ng container.

1. Add an apt Proxy setting echo 'Acquire::http { Proxy "http://dockerhost:3142"; };' >> /etc/apt/conf.d/01proxy
2. Set an environment variable: http_proxy=http://dockerhost:3142/
3. Change your sources.list entries to start with http://dockerhost:3142/
4. Link Debian-based containers to the APT proxy container using --link
5. Create a custom network of an APT proxy container with Debian-based containers.

Option 1 injects the settings safely into your apt configuration in a local version of a common base:

# syntax=docker/dockerfile:1
FROM ubuntu
RUN echo 'Acquire::http { Proxy "http://dockerhost:3142"; };' >> /etc/apt/apt.conf.d/01proxy
RUN apt-get update && apt-get install -y vim git

# docker build -t my_ubuntu .

Option 2 is good for testing, but breaks other HTTP clients which obey http_proxy, such as curl, wget and others:

$ docker run --rm -t -i -e http_proxy=http://dockerhost:3142/ debian bash

Option 3 is the least portable, but you might need to do it and you can do it from your Dockerfile too.

Option 4 links Debian-containers to the proxy server using following command:

$ docker run -i -t --link test_apt_cacher_ng:apt_proxy -e http_proxy=http://apt_proxy:3142/ debian bash

Option 5 creates a custom network of APT proxy server and Debian-based containers:

$ docker network create mynetwork
$ docker run -d -p 3142:3142 --network=mynetwork --name test_apt_cacher_ng eg_apt_cacher_ng
$ docker run --rm -it --network=mynetwork -e http_proxy=http://test_apt_cacher_ng:3142/ debian bash

Apt-cacher-ng has some tools that allow you to manage the repository, and they can be used by leveraging the VOLUME instruction, and the image we built to run the service:

$ docker run --rm -t -i --volumes-from test_apt_cacher_ng eg_apt_cacher_ng bash

root@f38c87f2a42d:/# /usr/lib/apt-cacher-ng/distkill.pl
Scanning /var/cache/apt-cacher-ng, please wait...
Found distributions:
bla, taggedcount: 0
     1. precise-security (36 index files)
     2. wheezy (25 index files)
     3. precise-updates (36 index files)
     4. precise (36 index files)
     5. wheezy-updates (18 index files)

Found architectures:
     6. amd64 (36 index files)
     7. i386 (24 index files)

WARNING: The removal action may wipe out whole directories containing
         index files. Select d to see detailed list.

(Number nn: tag distribution or architecture nn; 0: exit; d: show details; r: remove tagged; q: quit): q

Finally, clean up after your test by stopping and removing the container, and then removing the image.

$ docker container stop test_apt_cacher_ng
$ docker container rm test_apt_cacher_ng
$ docker image rm eg_apt_cacher_ng