Capistrano and Rake

Last night I read the chapter on automation in Tom Limoncelli’s book, Time Management for System Administrators. He spent a lot of time extolling the virtues of Make and how useful it can be in automating sysadmin tasks. Rails makes good use of Rake (think ‘ruby-make’) to specify administrative tasks. Make/Rake let you specify dependencies in your tasks and by checking file timestamps you can avoid running tasks unnecessarily. This has given me an idea for a change to the way deprec works.

It would be nice if I could restart mongrel on the server using the same command as I use in Capistrano. I’m not suggesting using Rake from my workstation but rather to have many of deprecs cap tasks call a Rake task on the server. So ‘cap deprec:mongrel:restart’ would call ‘rake deprec:mongrel:restart’ on the server(s).

There would be two main benefits to this.

Firstly, all deprec tasks would be available from the command line on the target host (obviously some bootstrapping would be required to install Rake, Ruby, etc initially). While I prefer not to have to log in manually to each of the servers in a cluster, there are times when I’m logged in and would like to be able to run tasks locally.

A second benefit is that we could take advantage of dependencies. Compiling PHP, after Apache has already been installed, will no longer cause Apache to be recompiled. Installing Subversion, when Apache has not already been installed, will cause it to be installed. This will reduce the amount of time tasks take to run (which is non-trivial when it involves compiling the likes of openssl!)

Back in May 2007, Bradley Taylor of Railsmachine released a nice gem called Machinify. It’s a set of Rake tasks that will install a Rails stack on Ubuntu. It’s very nicely written and quite readable. I considered whether I should make deprec dependent on Machinify but as it lacks some of the tasks I want (install, nginx, postgres, etc) I think it would be better for deprec come with its own Rake tasks.

So, it’s very tempting to re-architect deprec2 but another thing to consider is this: would we be better off with a working deprec2 next week or a re-designed deprec2 at some later point? I think working code is a better result than ideas that won’t get implemented in the available timeframe.

One issue with calling remote rake tasks via Cap is dealing with interactive dialogs. deprec currently deals with this by listening for certain output from the remote call. I can’t see why deprec couldn’t simply call the remote rake task and listen for the same output. This would allow deprec tasks to be extracted into rake tasks.

So my current thinking is to press on with deprec2 development and then extract the tasks into Rake tasks at some future point.