Running Rails 3.1.1 on Heroku

Heroku officially supports rails 3.1.1 on their Cedar stack now, unfortunately, you may still fail on deploy. The trouble maker is the assets:precompile rake task in rails 3.1. Heroku runs 'rake assets:precompile' for you when deploy, at a time many application dependencies, e.g. database server, redis, are NOT ready, so if there's any database/redis/any-other-not-ready-dependency use in your rails initialization process, assets:precompile will fail.

The tricky thing is, even you know the underlying theory, it's hard to find the exact place caused the problem, because heroku deployment do not use '--trace' flag when running precompile task, the limited error output is almost useless; and rails initialization process walks through so many files it's stupid to check them one by one.

For example, this is the error I got today when I deploy to heroku:

rake aborted!
bad URI(is not URI?):

Can you spot the broken code with so few information? I can't ... Fortunately, we can ask rake to give detail error stack without passing it '--trace' option, by adding this line in your Rakefile:

Rake.application.options.trace = true if %w(staging production).include?(Rails.env)

Then another problem pops up, I now found the broken code, how to fix it? Since the broken code uses something that is not ready when assets:precompile task running, an easy way would be:

# in Rakefile
if %w(staging production).include? Rails.env
$heroku_deploying = true if File.basename($0) == 'rake' && ARGV.include?('assets:precompile')
end

# in some initializers:
# reference to UsersController will trigger operation on database
provider :identity, :fields => [:name, :email, :nickname], :on_failed_registration => UsersController.action(:new) unless $heroku_deploying

With this duct tape kind fix, you may have $heroku_deploying scattered in your code .. it's ugly but works. Let me know if you have better idea :-)