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<p>Next, when a job is dequeued, we want to log that the worker picked up a job (needed for auditing purposes) and we alter the process name so if a process hangs, we know what that process
was attempting to run. If an unchecked exception occurs in a job, the worker will catch it and log it for us:</p>
<pre class="prettyprint">$worker-&gt;on( dequeue =&gt; sub( $worker, $job ) {
    my $id    = $job-&gt;id;
    my $notes = $job-&gt;info-&gt;{ notes };
    my $title = $notes-&gt;{ title };
    my $guid  = $notes-&gt;{ guid };

    $job-&gt;on( spawn =&gt; sub( $job, $pid ) {  
        $0 = "$title $guid";
        $logger-&gt;info( 
            "$title: Created child process $pid for job $id by parent $$ - $guid");
    });
        
    $job-&gt;on( failed =&gt; sub( $job, $error ) {
        chomp $error;
        $logger-&gt;error( $error );
    });
});</pre>

<p>To help us for future capacity planning, we want our workers to tell us if they are running at peak capacity, so log when this event occurs:</p>
<pre class="prettyprint">$worker-&gt;on( busy =&gt; sub( $worker ) {
    my $max = $worker-&gt;status-&gt;{ jobs };
    $logger-&gt;log( "$0: Running at capacity (performing $max jobs)." );
});</pre>

<p>Now, we apply the configuration (read below) to the worker. When the worker starts, it tells us information about how it was configured (this was really useful during development):</p>
<pre class="prettyprint">my $max_jobs = $hostconfig-&gt;{ max_children };
my @queues   = @{ $hostconfig-&gt;{ queues }};

if( $minion-&gt;has_invalid_queues( @queues ) ){
    print "Invalid job queues specified: " . join( ',', 
        $minion-&gt;get_invalid_queues( @queues ) );
    say ". Aborting!";
    exit 1;
}

say "Starting Job Queue Worker on " . get_hostname();
say "- Configured to run a max of $max_jobs jobs";
say "- Listening for jobs on queues: ", join(', ', @queues );
$worker-&gt;status-&gt;{ jobs }   = $max_jobs;
$worker-&gt;status-&gt;{ queues } = \@queues;
$worker-&gt;run;</pre>

<p>Remember the YAML file we used to configure things up above? This last bit pulls the information for the host this worker is running on (<code>get_hostname()</code> is a home-grown 
hostname function):</p>
<pre class="prettyprint">sub get_hostconfig {
    my $minion_config = 
        MyJob::Config-&gt;new({ filename =&gt; "environments/minions.yml" })-&gt;config;
    my $hostname      = get_hostname();

    if( exists $minion_config-&gt;{ $hostname }) {
        return $minion_config-&gt;{ $hostname };
    } else {
        return $minion_config-&gt;{ default };
    }
}</pre>

<h2><a name="monitoring_the_workers"></a>Monitoring the Workers</h2>

<p>Our Minion dashboard was virtually identical to the one that @preaction posted in <a href="https://mojolicious.io/blog/2018/12/11/who-watches-the-minions/#section-2">Who Watches the Minions?</a>.
If you'd like to know more, I highly recommend reading his article.</p>
<h2><a name="outcome"></a>Outcome</h2>

<p>Within about a two-week timespan, we went from having zero practical knowledge of Minion to having things up and running. We've made some refinements and improvements along the way, but the quick turnaround
is a true testament to the simplicity of working with Minion.</p>
<p>We now have all the necessary pieces in place to scale our XML rendering both horizontally and vertically: thanks to Minion, we can easily run XML jobs across multiple boxes, and can more efficiently run 
more jobs concurrently on the same hardware as before. This setup allows us to grow as quickly as our customer base does.</p>
<h2><a name="author"></a>Author</h2>

<p>This article has been written by Jason Crome (CromeDome) for the Perl Dancer 
Advent Calendar 2018.</p>
<h2><a name="copyright"></a>Copyright</h2>

<p>No copyright retained. Enjoy.</p>
<p>Jason A. Crome</p>
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