mirror of
https://github.com/privatevoid-net/nix-super.git
synced 2024-11-10 16:26:18 +02:00
116 lines
5.5 KiB
XML
116 lines
5.5 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
|
||
xmlns:xlink="http://www.w3.org/1999/xlink"
|
||
xmlns:xi="http://www.w3.org/2001/XInclude"
|
||
version="5.0"
|
||
xml:id='chap-distributed-builds'>
|
||
|
||
<title>Distributed Builds</title>
|
||
|
||
<para>Nix supports distributed builds, where a local Nix installation can
|
||
forward Nix builds to other machines over the network. This allows
|
||
multiple builds to be performed in parallel (thus improving
|
||
performance) and allows Nix to perform multi-platform builds in a
|
||
semi-transparent way. For instance, if you perform a build for a
|
||
<literal>x86_64-darwin</literal> on an <literal>i686-linux</literal>
|
||
machine, Nix can automatically forward the build to a
|
||
<literal>x86_64-darwin</literal> machine, if available.</para>
|
||
|
||
<para>You can enable distributed builds by setting the environment
|
||
variable <envar>NIX_BUILD_HOOK</envar> to point to a program that Nix
|
||
will call whenever it wants to build a derivation. The build hook
|
||
(typically a shell or Perl script) can decline the build, in which Nix
|
||
will perform it in the usual way if possible, or it can accept it, in
|
||
which case it is responsible for somehow getting the inputs of the
|
||
build to another machine, doing the build there, and getting the
|
||
results back. The details of the build hook protocol are described in
|
||
the documentation of the <link
|
||
linkend="envar-build-hook"><envar>NIX_BUILD_HOOK</envar>
|
||
variable</link>.</para>
|
||
|
||
<example xml:id='ex-remote-systems'><title>Remote machine configuration:
|
||
<filename>remote-systems.conf</filename></title>
|
||
<programlisting>
|
||
nix@mcflurry.labs.cs.uu.nl x86_64-darwin /home/nix/.ssh/id_quarterpounder_auto 2
|
||
nix@scratchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 1 kvm
|
||
nix@itchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 2
|
||
nix@poochie.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 2 kvm perf
|
||
</programlisting>
|
||
</example>
|
||
|
||
<para>Nix ships with a build hook that should be suitable for most
|
||
purposes. It uses <command>ssh</command> and
|
||
<command>nix-copy-closure</command> to copy the build inputs and
|
||
outputs and perform the remote build. To use it, you should set
|
||
<envar>NIX_BUILD_HOOK</envar> to
|
||
<filename><replaceable>prefix</replaceable>/libexec/nix/build-remote</filename>.
|
||
You should also define a list of available build machines and point
|
||
the environment variable <envar>NIX_REMOTE_SYSTEMS</envar> to
|
||
it. <envar>NIX_REMOTE_SYSTEMS</envar> must be an absolute path. An
|
||
example configuration is shown in <xref linkend='ex-remote-systems'
|
||
/>. Each line in the file specifies a machine, with the following
|
||
bits of information:
|
||
|
||
<orderedlist>
|
||
|
||
<listitem><para>The name of the remote machine, with optionally the
|
||
user under which the remote build should be performed. This is
|
||
actually passed as an argument to <command>ssh</command>, so it can
|
||
be an alias defined in your
|
||
<filename>~/.ssh/config</filename>.</para></listitem>
|
||
|
||
<listitem><para>A comma-separated list of Nix platform type
|
||
identifiers, such as <literal>x86_64-darwin</literal>. It is
|
||
possible for a machine to support multiple platform types, e.g.,
|
||
<literal>i686-linux,x86_64-linux</literal>.</para></listitem>
|
||
|
||
<listitem><para>The SSH private key to be used to log in to the
|
||
remote machine. Since builds should be non-interactive, this key
|
||
should not have a passphrase!</para></listitem>
|
||
|
||
<listitem><para>The maximum number of builds that
|
||
<filename>build-remote</filename> will execute in parallel on the
|
||
machine. Typically this should be equal to the number of CPU cores.
|
||
For instance, the machine <literal>itchy</literal> in the example
|
||
will execute up to 8 builds in parallel.</para></listitem>
|
||
|
||
<listitem><para>The “speed factor”, indicating the relative speed of
|
||
the machine. If there are multiple machines of the right type, Nix
|
||
will prefer the fastest, taking load into account.</para></listitem>
|
||
|
||
<listitem><para>A comma-separated list of <emphasis>supported
|
||
features</emphasis>. If a derivation has the
|
||
<varname>requiredSystemFeatures</varname> attribute, then
|
||
<filename>build-remote</filename> will only perform the
|
||
derivation on a machine that has the specified features. For
|
||
instance, the attribute
|
||
|
||
<programlisting>
|
||
requiredSystemFeatures = [ "kvm" ];
|
||
</programlisting>
|
||
|
||
will cause the build to be performed on a machine that has the
|
||
<literal>kvm</literal> feature (i.e., <literal>scratchy</literal> in
|
||
the example above).</para></listitem>
|
||
|
||
<listitem><para>A comma-separated list of <emphasis>mandatory
|
||
features</emphasis>. A machine will only be used to build a
|
||
derivation if all of the machine’s mandatory features appear in the
|
||
derivation’s <varname>requiredSystemFeatures</varname> attribute.
|
||
Thus, in the example, the machine <literal>poochie</literal> will
|
||
only do derivations that have
|
||
<varname>requiredSystemFeatures</varname> set to <literal>["kvm"
|
||
"perf"]</literal> or <literal>["perf"]</literal>.</para></listitem>
|
||
|
||
</orderedlist>
|
||
|
||
You should also set up the environment variable
|
||
<envar>NIX_CURRENT_LOAD</envar> to point at a directory (e.g.,
|
||
<filename>/var/run/nix/current-load</filename>) that
|
||
<filename>build-remote</filename> uses to remember how many builds
|
||
it is currently executing remotely. It doesn't look at the actual
|
||
load on the remote machine, so if you have multiple instances of Nix
|
||
running, they should use the same <envar>NIX_CURRENT_LOAD</envar>
|
||
file. Maybe in the future <filename>build-remote</filename> will
|
||
look at the actual remote load.</para>
|
||
|
||
</chapter>
|