:title: Running an apt-cacher-ng service
:description: Installing and running an apt-cacher-ng service
:keywords: docker, example, package installation, networking, debian, ubuntu

.. _running_apt-cacher-ng_service:

Apt-Cacher-ng Service
=====================

.. include:: example_header.inc


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:

.. literalinclude:: apt-cacher-ng.Dockerfile

To build the image using:

.. code-block:: bash

    $ sudo docker build -t eg_apt_cacher_ng .

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

.. code-block:: bash

    $ sudo 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: 

.. code-block:: bash

    $ sudo docker logs -f test_apt_cacher_ng

To get your Debian-based containers to use the proxy, you can do one of three things

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/``

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

.. code-block:: bash

    FROM ubuntu
    RUN  echo 'Acquire::http { Proxy "http://dockerhost:3142"; };' >> /etc/apt/apt.conf.d/01proxy
    RUN apt-get update ; apt-get install vim git

    # docker build -t my_ubuntu .

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

.. code-block:: bash

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

**Option 3** is the least portable, but there will be times when you might need to
do it and you can do it from your ``Dockerfile`` too.

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:

.. code-block:: bash

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

    $$ /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.

.. code-block:: bash

    $ sudo docker stop test_apt_cacher_ng
    $ sudo docker rm test_apt_cacher_ng
    $ sudo docker rmi eg_apt_cacher_ng