title: Postgres in Docker persistent data
body: <p>I'm running postgres inside a docker container to limit the amount of system resources it has access to.  I'm having some trouble understanding how to make the data persistent.  I've read the following articles:</p>
  
  <p><a href="https://www.andreagrandi.it/2015/02/21/how-to-create-a-docker-image-for-postgresql-and-persist-data/" rel="nofollow">https://www.andreagrandi.it/2015/02/21/how-to-create-a-docker-image-for-postgresql-and-persist-data/</a></p>
  
  <p><a href="http://container42.com/2013/12/16/persistent-volumes-with-docker-container-as-volume-pattern/" rel="nofollow">http://container42.com/2013/12/16/persistent-volumes-with-docker-container-as-volume-pattern/</a></p>
  
  <p>Which suggest using a data only container, and then having my postgres container link to it.  What I'm failing to understand is; what's the advantage to this?  As far as I can tell, if for some reason the docker-machine shut down (for example; moving it to a different physical machine), the data only container stops running, and all of it's contents are lost?  I've tried creating a volume in the postgres container, but it doesn't actually seem to save anything to the disk.</p>
  
  <p>Here's my docker file.  What am I doing wrong?</p>
  
  <pre><code>FROM ubuntu
  MAINTAINER Andrew Broadbent &lt;andrew.broadbent@manchester.ac.uk&gt;
  
  # Add the PostgreSQL PGP key to verify their Debian packages.
  # It should be the same key as https://www.postgresql.org/media/keys/ACCC4CF8.asc
  RUN apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys B97B0AFCAA1A47F044F244A07FCC7D46ACCC4CF8
  
  # Add PostgreSQL's repository. It contains the most recent stable release
  #     of PostgreSQL, ``9.3``.
  RUN echo "deb http://apt.postgresql.org/pub/repos/apt/ precise-pgdg main" &gt; /etc/apt/sources.list.d/pgdg.list
  
  # Install ``python-software-properties``, ``software-properties-common`` and PostgreSQL 9.3
  #  There are some warnings (in red) that show up during the build. You can hide
  #  them by prefixing each apt-get statement with DEBIAN_FRONTEND=noninteractive
  RUN apt-get update &amp;&amp; apt-get install -y python-software-properties software-properties-common postgresql-9.3 postgresql-client-9.3 postgresql-contrib-9.3
  
  # Note: The official Debian and Ubuntu images automatically ``apt-get clean``
  # after each ``apt-get``
  
  # Run the rest of the commands as the ``postgres`` user created by the ``postgres-9.3`` package when it was ``apt-get installed``
  USER postgres
  
  # Create a PostgreSQL role named ``docker`` with ``docker`` as the password and
  # then create a database `docker` owned by the ``docker`` role.
  # Note: here we use ``&amp;&amp;\`` to run commands one after the other - the ``\``
  #       allows the RUN command to span multiple lines.
  RUN    /etc/init.d/postgresql start &amp;&amp;\
      psql --command "CREATE USER docker WITH SUPERUSER PASSWORD 'docker';" &amp;&amp;\
      createdb -O docker docker
  
  # Complete configuration
  USER root
  RUN echo "host all  all    0.0.0.0/0  md5" &gt;&gt; /etc/postgresql/9.3/main/pg_hba.conf
  RUN echo "listen_addresses='*'" &gt;&gt; /etc/postgresql/9.3/main/postgresql.conf
  
  # Expose the PostgreSQL port
  EXPOSE 5432
  
  # Add VOLUMEs to allow backup of config, logs and databases
  RUN mkdir -p /var/run/postgresql &amp;&amp; chown -R postgres /var/run/postgresql
  VOLUME  ["/etc/postgresql", "/var/log/postgresql", "/var/lib/postgresql"]
  
  # Set the default command to run when starting the container
  USER postgres
  CMD ["/usr/lib/postgresql/9.3/bin/postgres", "-D", "/var/lib/postgresql/9.3/main", "-c", "config_file=/etc/postgresql/9.3/main/postgresql.conf"]
  </code></pre>