Digital Digressions by Stuart Sierra

I decided to run AltLaw.org under a “/v1” URL prefix. It’s still beta, and the URL structure will likely change in the future. I don’t want to break 160,000 links when that day comes. Fortunately, Mongrel makes this pretty easy with the –prefix option to mongrel_rails.

I added --prefix '/v1' to my mongrel_rails command line. After removing absolute URLs (those not using {:controller=>...}) from my views, everything worked great.

The only problem is, this technique prevents Apache from serving static files without hitting the Mongrel server. A typical mod_rewrite directive like this:

RewriteCond %{DOCUMENT_ROOT}%{REQUEST_URI} -f
RewriteRule (.*) $1 [L]

doesn’t work, because the REQUEST_URIs now all start with “/v1” and the files in “MyRailsApp/public” don’t.

Here’s a simple workaround: make a symlink like this:

cd /path/to/MyRailsApp/public
ln -s . v1

That’s right, “v1” is a symlink that points back to the “public” directory. I was afraid this might cause an infinite loop, but it doesn’t. Keeping the same mod_rewrite rule above, Apache will serve the static files under “public” even if the request is prefixed with “/v1”. Pretty cool.

I’ve used Darcs as my only version-control system for a while now. When I got into Rails, I naturally wanted to use Capistrano. Unfortunately, Darcs and Capistrano don’t get along too well. Darcs’ file-based repositories don’t mesh well with Capistrano’s assumption that the repository is accessed through a server, a la Subversion.

I ran into problems with cap deploy:update_code because Darcs couldn’t find the repository. After a discussion on the Capistrano mailing list I decided to go my own route.

I have two Darcs repositories, one on my development machine and one on the server. I darcs push patches from development to the server. Then I have my own custom Capistrano tasks to get the latest code from the server’s copy of the repository. This is adapted from the Capistrano sources:

namespace :deploy do
  task :update_code, :except => { :no_release => true } do
    on_rollback { run "rm -rf #{release_path}; true" }

    run("darcs get --partial /home/myapp/repo --repo-name=#{release_path}")
    run("rm -rf #{release_path}/_darcs")

    finalize_update
  end
end

I also had to write a custom finalize_update task to add the links to the shared Rails directories:

namespace :deploy do
  task :finalize_update, :except => { :no_release => true } do
    run <<-CMD
      ln -s #{shared_path}/log   #{latest_release}/log &&
      ln -s #{shared_path}/tmp   #{latest_release}/tmp &&
      ln -s #{shared_path}/data  #{latest_release}/data &&
      ln -s #{shared_path}/index #{latest_release}/index &&
      ln -s #{shared_path}/config/database.yml #{latest_release}/config/database.yml &&
      ln -s #{shared_path}/public/system #{latest_release}/public/system
     CMD
  end
end

Trying to set up Apache2 as a proxy for mongrel on my new Ruby on Rails server, following the instructions on the mongrel site. I kept getting “403 Forbidden” errors on every request. I found a comment that seemed to describe the same situation. Sure enough, editing /etc/apache2/mods-enabled/proxy.conf to change “Deny” to “Allow” fixed the problem. I kept ProxyRequests turned off, which is supposed to prevent my site from becoming an open proxy, but I’m still nervous about removing that “Deny” directive. I wish there were a more authoritative source of information on this.