Kopongo

I just ran into a neat little capistrano trick. I have been making some changes to an app, and knew it had been a while since I had made a release to one of the apps I am working on. But which version do I have installed?

I tried the cap diff_from_last_deploy, but it was a little too much information. I ran into capistrano's stream command, and that proved to be just right:

    desc "Find out svn version on server"
    task :what_version, :roles => [:app] do
        stream <<-CMD
            svn info #{current_path}/app
        CMD
    end

It's also useful for those one-off commands you might want to run on your server, like seeing how many users registered at your site:

    desc "Find out how many users are registered"
    task :how_many_users, :roles => [:app] do
        stream <<-CMD
            psql -U user -d yourapp_production -c 'select count(login) from users'
        CMD
    end

If you are using google maps in your apps, you get special key from them that works for the URL where you want to use the maps (ie www.yoursite.com). Since you probably test your code on localhost before you deploy it, you have a problem. The key they give you only works at that URL. What you need to do is get another key that works with your testing on your localhost, for example for localhost:3000.

What this means that when you deploy, you have to switch them. Of course, you do not want to do this by hand.

Here's a simple way to do this with capistrano:

    task :after_update_code, :roles => [:app, :db, :web] do

       layout_file = File.read('app/views/layouts/standard.rhtml')
       google_map_key = File.read("config/google_map_key.txt")
       layout_file.sub!(/file=api&v=2&key=(\w+)/, "file=api&v=2&key=#{google_map_key}")
       put(layout_file,
           "#{release_path}/app/views/layouts/standard.rhtml",
           :mode => 0444)
    end

So, what's going on?

First, save the production key on some file, like config/googlemapkey.txt. Don't think that is is like saving database passwords in SVN, since this key appears on all your webpages anyway.

I put my key in the site layout I use, standard.rhtml. By default, you want to keep development version of the key in there. When we deploy, we read the key from googlemapkey.txt, use a regexp to switch the development key with the production key. Then we send that file over with the put command.

You could be more clever by changing the file that's already on the server, instead of changing the local file and sending it over, but this works well enough.