I was moving a Rails 2 app up to Rails 3 and, because I have PostgreSQL installed in a non-standard location on my server, I ran into problems when bundler was trying to install the pg gem. After fiddling about for a bit I ended up with this in my config/deploy.rb:
require 'bundler/capistrano'
task :set_config_for_pg_gem, :roles => [:app, :db] do
run "cd #{current_path} && bundle config build.pg --with-pg-config=/usr/local/pgsql/bin/pg_config --no-rdoc --no-ri"
end
before "bundle:install", :set_config_for_pg_gem
This sets up the appropriate command line flags for the pg gem so that they're in place when Capistrano runs the bundle:install task. The --no-rdoc --no-ri part isn't necessary, but I figured it'll save a second or two. Note that these flags end up in the deploy user's home directory on the server:
$ cat ~/.bundle/config --- BUNDLE_BUILD__PG: --with-pg-config=/usr/local/pgsql/bin/pg_config --no-rdoc --no-ri
Running this task every time you deploy is a little wasteful since it sets the configuration unnecessarily - really you just need it before the first time you deploy. So you could optimize things by touching a file in shared/system/ or some such and checking it as part of this task.