I would like to get some advices - I am writing a web application
that will be sending some emails and execute other long running tasks.
Some of these tasks may take some time and I do not want the user
experience to be impacted. I would appreciate any pointers on advices
on these areas:
* how to send emails without making the user wait
* how to execute long running tasks
* The best way to do periodic cron jobs in Rails
Either Thread.new{}, or a plugin called Spawn. You need the latter if your e-mails call templates which in turn call ActiveRecord. A separate thread requires a separate database connection, and Spawn handles this.
* how to execute long running tasks
The threading option has one flaw: If your web server expunges your Passenger module from memory, the thread lapses.
When sending a few emails, if you can't send them before process harvesting time, you have bigger problems than a missing email. Failing that analysis, you need an out-of-process solution like BackgroundRB. It runs in a daemon of its own and communicates with your app thru dRB. In exchange for a fatter and more fragile implementation, you get a process you can control directly. However...
* The best way to do periodic cron jobs in Rails
Create a folder called cron, write (using TDD!) a script that does what you need, and install it into your OS's cron system as the command line script/runner lib/my_script.rb.
If I needed to send e-mails, I would pool them up, then push them out with a cron. The previous two options allow communication back to the user in subsequent controller actions. You probably don't need that, so just configure a cron to run every 90 seconds, and send emails for up to 1 minute. Take a little care to not send the same email twice, and you are set.
For emails, the simplest way is to set up a local MTA (postfix, for
instance) and send the mail to that. The MTA takes care of the hard
part delivering the mail as needed.
For more general things, there are some gems that let you set up cron-
like tasks, or you can just call a rake task from plain old cron.