Scheduled tasks using BackgrounDRb

A project I am working on required a background process to check and update subscriptions nightly, and send out billing emails to users with expiring subscriptions. I decided to use BackgrounDRb, a plugin perfectly suited for this task.

Setting up:
BackgronDRb runs as a separate server, but is just a process with access to all your Rails models.

<br /><br />
# Generate a worker model:<br /><br />
script/generate worker billing<br /><br />

This generates a worker called BillingWorker in lib/workers. My billing_worker.rb goes like this:

<br /><br />
class BillingWorker < BackgrounDRb::MetaWorker</p><br />
<p>set_worker_name :billing_worker</p><br />
<p>def create(args=nil)</p><br />
<p>end</p><br />
<p>def do_nightly_updates<br /><br />
Subscription.run_notify<br /><br />
end</p><br />
<p>

</p><br />
<p>#In subscription.rb:<br /><br />
class Subscription < ActiveRecord::Base<br /><br />
def notify!<br /><br />
UserMailer.deliver_expiring_subscription_notification(subscription)<br /><br />
end</p><br />
<p>def self.run_notify<br /><br />
find( :all, :conditions =&amp;amp;amp;amp;gt; ['send_notice=?', true] ).each(&amp;amp;amp;amp;amp;:notify!)<br /><br />
end<br /><br />
end<br /><br />

To trigger the worker process to perform its task at 12:01 a.m. every day, my background.yml reads:

<br /><br />
:backgroundrb:<br /><br />
:ip: 0.0.0.0<br /><br />
:port: 11006<br /><br />
:schedules:<br /><br />
:billing_worker:<br /><br />
:do_nightly_updates:<br /><br />
# Trigger this action at 12:01 a.m. every day<br /><br />
:trigger_args: 0 1 0 * * * *<br /><br />

Re the BackgrounDRb cron trigger, here’s a snippet from the plugin docs :

Note that the initial field in the BackgrounDRb cron trigger specifies seconds, not minutes as with Unix-cron. The fields (which can be an asterisk, meaning all valid patterns) are:

<br /><br />
sec[0,59] min[0,59], hour[0,23], day[1,31], month[1,12], weekday[0,6], year</p><br />
<p># The syntax pretty much follows Unix-cron. The following will trigger on the first hour and the thirtieth minute every day:<br /><br />
0 30 1 * * * *</p><br />
<p># The following will trigger the specified method every 10 seconds:<br /><br />
*/10 * * * * * *</p><br />
<p># The following will trigger the specified method every 1 hour:<br /><br />
0 0 * * * * *<br /><br />

(Aside) If you’re developing on a Mac like I am, you may want to use

</p><br />
<p>:ip: 0.0.0.0</p><br />
<p># instead of<br /><br />
:ip: localhost<br /><br />

for things to run smoothly

Run it!
Fire up two Terminal windows, one to start and stop the BackgrounDRb server, and the other one to monitor the log file:

<br /><br />
script/backgroundrb start<br /><br />

Everything is hunky-dory right now, I just need to do two further tasks:

1. Write specs for my worker model – I can’t seem to mock my model correctly, I keep getting undefined constants errors when running autotest.

2. Have a BackgrounDRb process upload images to S3 in the background using Paperclip.