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<title>s6: the s6-instance-maker program</title>
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<p>
<a href="index.html">s6</a><br />
<a href="//skarnet.org/software/">Software</a><br />
<a href="//skarnet.org/">skarnet.org</a>
</p>
<h1> The s6-instance-maker program </h1>
<p>
s6-instance-maker creates a <a href="servicedir.html">service directory</a>
implementing an <a href="instances.html">instanced service</a>. Give it a
templated service directory describing how to run an instance of a service,
and it will create a different service directory that can launch and
manage several instances; each of these instances will be running a
copy of the service directory you gave.
</p>
<p>
Alternatively, s6-instance-maker can create source definition directories
for the <a href="//skarnet.org/software/s6-rc/">s6-rc</a> service manager.
</p>
<h2> Interface </h2>
<pre>
s6-instance-maker \
[ -c <em>maxinstances</em> ] \
[ -r <em>service</em>[/<em>logger</em>[/<em>pipeline</em>]] ] \
[ -u <em>user</em> ] \
[ -l <em>loguser</em> ] \
[ -L <em>logdir</em> ] \
[ -t <em>stamptype</em> ] \
[ -n <em>nfiles</em> ] \
[ -s <em>filesize</em> ] \
[ -S <em>maxsize</em> ] \
[ -P <em>prefix</em> ] \
template dir
</pre>
<p>
s6-instance-maker creates a service directory in <em>dir</em> (which must
not already exist). The created service will be a supervisor for a set of
instances — initially empty —
each running a copy of the service directory given in <em>template</em>.
</p>
<p>
s6-instance-maker is an <em>offline</em> tool: it is run before you need
instances. Once the created service directory is live, i.e. there is a
supervisor running on it, then you can create, delete, or control
individual instances via the
<a href="s6-instance-create.html">s6-instance-create</a>,
<a href="s6-instance-delete.html">s6-instance-delete</a> and
<a href="s6-instance-control.html">s6-instance-control</a> <em>online</em>
tools, that work with active services.
</p>
<h2> Exit codes </h2>
<ul>
<li> 0: success </li>
<li> 100: wrong usage </li>
<li> 111: system call failed </li>
</ul>
<h2> Options </h2>
<ul>
<li> <tt>-c</tt> <em>max</em> : Plan for a maximum of <em>max</em>
instances. Default is <strong>500</strong>. You can't set it lower than 2 or
higher than 90000. If your template service directory is logged, it's unadvisable
to set this above the default. </li> <br>
<li> <tt>-r</tt> <em>service</em>[/<em>logger</em>[/<em>pipeline</em>]] :
create <a href="//skarnet.org/software/s6-rc">s6-rc</a> source definition directories.
When this option is given, <em>dir</em> is not created as a service directory, but
as a directory containing at least one service: <em>dir</em>/<em>service</em>.
<em>dir</em> is suitable as a source argument to
<a href="//skarnet.org/software/s6-rc/s6-rc-compile.html">s6-rc-compile</a>. If
a <em>logger</em> part is given, then a second service, <em>dir</em>/<em>logger</em>,
is also created, as a consumer for <em>dir</em>/<em>service</em>, and the <tt>-L</tt>
option must also be used, to provide a directory to store the logs into. If the
<tt>/</tt><em>pipeline</em> part is also given, <em>pipeline</em>
is used as a name for a bundle containing both <em>service</em> and <em>logger</em>.
When the <tt>-r</tt> option is not given at all, <em>dir</em> is a regular service
directory for direct inclusion (or linking) in a host
<a href="scandir.html">scan directory</a>, and if the <tt>-L</tt> option is given
then the logger for the instance supervisor and all its instances is declared in
<em>dir</em><tt>/log</tt>. </li> <br>
<li> <tt>-u</tt> <em>user</em> : run the instance supervisor, and all
of the instances, as user <em>user</em>. This option should only be used when the
supervision tree that will host the instanced service is run as root. The default
is that the service runs as the same user as the host supervision tree. </li> <br>
<li> <tt>-l</tt> <em>loguser</em> : run the logger of the instance
supervisor, if any (see <tt>-L</tt> below) as user <em>loguser</em>. This option
should only be used when the
supervision tree that will host the instanced service is run as root. The default
is that the logger runs as the same user as the host supervision tree. </li> <br>
<li> <tt>-L</tt> <em>logdir</em> : make the service logged via
<a href="s6-log.html">s6-log</a>, and ensure its log messages go into <em>logdir</em>.
Error messages from the instance supervisor as well as from every instance will
be logged to <em>logdir</em>. If this option is not given, these error messages
will fall through to the host supervision tree's catch-all logger, if any,
or standard error otherwise. <br>
The options listed below are only used to configured the logger and are meaningless
if <tt>-L</tt> is not given. </li> <br>
<li> <tt>-t</tt> <em>stamptype</em> : how
logs are timestamped in <em>logdir</em>. 0 means no timestamp, 1 means
<a href="https://cr.yp.to/libtai/tai64.html">external TAI64N format</a>,
2 means
<a href="https://www.iso.org/iso/home/standards/iso8601.htm">ISO 8601 format</a>,
and 3 means both. Default is <strong><tt>1</tt></strong>. </li> <br>
<li> <tt>-n</tt> <em>nfiles</em> : maximum number of archive files
in <em>logdir</em>. Default is <strong><tt>10</tt></strong>. </li> <br>
<li> <tt>-s</tt> <em>filesize</em> : maximum size of the <tt>current</tt>
file (and archive files) in <em>logdir</em>. Default is <strong><tt>1000000</tt></strong>. </li> <br>
<li> <tt>-S</tt> <em>maxsize</em> : maximum total size of the
archives in <em>logdir</em>. Default is <strong><tt>0</tt></strong>,
meaning no limits apart from those enforced by the <tt>-n</tt> and
<tt>-s</tt> options. </li> <br>
<li> <tt>-P</tt> <em>prefix</em> : when logging to <em>logdir</em>,
prefix logged lines with the <em>prefix</em> string. Default is no prefix. </li>
</ul>
<h2> The templated service directory </h2>
<p>
<em>template</em> should be a directory that looks exactly like a service
directory. It will not be live, i.e. at no point will <em>template</em>
itself be supervised; instead, a copy of it is stored under <em>dir</em>
(and a copy of that copy will be used for every instance of the service).
You can safely move or delete <em>template</em> after running
s6-instance-maker.
</p>
<p>
To differentiate between instances, the <tt>run</tt> and <tt>finish</tt>
script in <em>template</em> should take one additional argument (the
first argument for <tt>run</tt> and the third argument for <tt>finish</tt>).
This argument will be the name of the instance, as provided by the
<a href="s6-instance-create.html">s6-instance-create</a> invocation.
</p>
<h2> Logging </h2>
<p>
The service is logged: its stderr and stdout are piped to an
<a href="s6-log.html">s6-log</a> process running as <em>loguser</em> and
writing to the <em>logdir</em> directory. This logger is the catch-all logger
for the supervision tree owned by <em>user</em>; it is recommended to make
<em>loguser</em> distinct from <em>user</em>, and to have <em>logdir</em>
in a place that is <strong>not</strong> under the control of <em>user</em>.
If <em>user</em> wants to keep control of their logs, they can declare a
logger for each of their services.
</p>
<p>
If <em>template</em> has a <em>log</em> subdirectory, then each instance
will have its own dedicated logger. The <tt>run</tt> and <tt>finish</tt>
scripts for the logger of an instance named <em>name</em> will be called
with an additional argument of <tt><em>name</em>/log</tt>. They should
make use of this, to ensure loggers are properly differentiated between
instances: for instance, it is not possible to run several
<a href="s6-log.html">s6-log</a> processes on the same log directory,
so an instance logger script containing an invocation of s6-log on a fixed
logdir will fail as soon as there are 2 instances.
</p>
<h2> Notes </h2>
<ul>
<li> s6-instance-maker makes use of the fact that
<a href="//skarnet.org/software/execline/">execline</a> scripts are much
easier to generate programmatically and to harden than shell scripts, so it is only
built if s6 is built with <a href="//skarnet.org/software/execline/">execline</a>
support - i.e. the <tt>--disable-execline</tt> switch has <em>not</em> been given
to configure. </li>
<li> If s6-instance-maker encounters failure (and exits 111), it does not clean up
the directories it created. Make sure to always test s6-instance-maker's return code
and clean up after it if needed. </li>
</ul>
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