<chapter xmlns="http://docbook.org/ns/docbook"
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         xml:id="chap-installation">

  <title>Installation</title>

  <para>
    This chapter explains how to install Hydra on your own build farm server.
  </para>

  <section>
    <title>Prerequisites</title>
    <para>
      To install and use Hydra you need to have installed the following dependencies:

      <itemizedlist>
        <listitem><para>Nix</para></listitem>
        <listitem><para>PostgreSQL</para></listitem>
        <listitem><para>many Perl packages, notably Catalyst, EmailSender,
        and NixPerl (see the <link
        xlink:href="https://github.com/NixOS/hydra/blob/master/release.nix">Hydra
        expression in Nixpkgs</link> for the complete
        list)</para></listitem>
      </itemizedlist>

      At the moment, Hydra runs only on GNU/Linux
      (<emphasis>i686-linux</emphasis> and
      <emphasis>x86_64_linux</emphasis>).
    </para>

    <para>
      For small projects, Hydra can be run on any reasonably modern
      machine. For individual projects you can even run Hydra on a
      laptop. However, the charm of a buildfarm server is usually that
      it operates without disturbing the developer's working
      environment and can serve releases over the internet. In
      conjunction you should typically have your source code
      administered in a version management system, such as
      subversion. Therefore, you will probably want to install a
      server that is connected to the internet. To scale up to large
      and/or many projects, you will need at least a considerable
      amount of diskspace to store builds. Since Hydra can schedule
      multiple simultaneous build jobs, it can be useful to have a
      multi-core machine, and/or attach multiple build machines in a
      network to the central Hydra server.
    </para>

    <para>
      Of course we think it is a good idea to use the <link
      xlink:href="http://nixos.org/nixos">NixOS</link> GNU/Linux
      distribution for your buildfarm server. But this is not a
      requirement.  The Nix software deployment system can be
      installed on any GNU/Linux distribution in parallel to the
      regular package management system. Thus, you can use Hydra on a
      Debian, Fedora, SuSE, or Ubuntu system.
    </para>

  </section>

  <section>
    <title>Getting Nix</title>

    <para>
      If your server runs NixOS you are all set to continue with
      installation of Hydra. Otherwise you first need to install Nix.
      The latest stable version can be found one <link
      xlink:href="http://nixos.org/nix/download.html">the Nix web
      site</link>, along with a manual, which includes installation
      instructions.
    </para>
  </section>

  <section>
    <title>Installation</title>

<!--
    <para>
      Hydra can be installed using Nixpkgs:

      <screen>
nix-env -f /path/to/nixpkgs -iA hydra</screen>

      This makes the tools available in your Nix user environment,
      <literal>$HOME/.nix-profile</literal> by default.
    </para>
-->

    <para>
      The latest development snapshot of Hydra can be installed
      by visiting the URL <link
      xlink:href="http://hydra.nixos.org/view/hydra/unstable"><literal>http://hydra.nixos.org/view/hydra/unstable</literal></link>
      and using the one-click install available at one of the build
      pages. You can also install Hydra through the channel by
      performing the following commands:

<screen>
nix-channel --add http://hydra.nixos.org/jobset/hydra/master/channel/latest
nix-channel --update
nix-env -i hydra</screen>
    </para>

    <para>
      Command completion should reveal a number of command-line tools
      from Hydra, such as <command>hydra-queue-runner</command>.
    </para>
  </section>

  <section>
    <title>Creating the database</title>
    <para>
      Hydra stores its results in a PostgreSQL database.
    </para>

    <para>
      To setup a PostgreSQL database with <emphasis>hydra</emphasis>
      as database name and user name, issue the following commands on
      the PostgreSQL server:

      <screen>
createuser -S -D -R -P hydra
createdb -O hydra hydra</screen>

      Note that <emphasis>$prefix</emphasis> is the location of Hydra
      in the nix store.
    </para>

    <para>
      Hydra uses an environment variable to know which database should
      be used, and a variable which point to a location that holds
      some state. To set these variables for a PostgreSQL database,
      add the following to the file <filename>~/.profile</filename> of
      the user running the Hydra services.

      <screen>
export HYDRA_DBI="dbi:Pg:dbname=hydra;host=dbserver.example.org;user=hydra;"
export HYDRA_DATA=/var/lib/hydra</screen>

      You can provide the username and password in the file
      <filename>~/.pgpass</filename>, e.g.

      <screen>
dbserver.example.org:*:hydra:hydra:password</screen>

      Make sure that the <emphasis>HYDRA_DATA</emphasis> directory
      exists and is writable for the user which will run the Hydra
      services. 
    </para>

    <para>
      Having set these environment variables, you can now initialise
      the database by doing:
      <screen>
hydra-init</screen>
    </para>

    <para>
      To create projects, you need to create a user with
      <emphasis>admin</emphasis> privileges.  This can be done using
      the command <command>hydra-create-user</command>:

<screen>
$ hydra-create-user alice --full-name 'Alice Q. User' \
    --email-address 'alice@example.org' --password foobar --role admin
</screen>

      Additional users can be created through the web interface.
    </para>

  </section>

  <section>
    <title>Upgrading</title>

    <para>If you're upgrading Hydra from a previous version, you
    should do the following to perform any necessary database schema migrations:
      <screen>
hydra-init</screen>
    </para>

  </section>

  <section>
    <title>Getting Started</title>

    <para>
      To start the Hydra web server, execute:
      <screen>
hydra-server</screen>

      When the server is started, you can browse to
      <ulink>http://localhost:3000/</ulink> to start configuring
      your Hydra instance.
    </para>

    <para>
      The <command>hydra-server</command> command launches the web
      server.  There are two other processes that come into play:

      <itemizedlist>
        <listitem>
          The <emphasis>evaluator</emphasis> is responsible for
          periodically evaluating job sets, checking out their
          dependencies off their version control systems (VCS), and
          queueing new builds if the result of the evaluation changed.
          It is launched by the <command>hydra-evaluator</command>
          command.
        </listitem>
        <listitem>
          The <emphasis>queue runner</emphasis> launches builds (using
          Nix) as they are queued by the evaluator, scheduling them
          onto the configured Nix hosts.  It is launched using the
          <command>hydra-queue-runner</command> command.
        </listitem>
      </itemizedlist>

      All three processes must be running for Hydra to be fully
      functional, though it's possible to temporarily stop any one of
      them for maintenance purposes, for instance.
    </para>

  </section>

</chapter>

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