Capistrano 2, Multistage, and Mongrel Clusters

Recently I have been configuring Mongrel and Capistrano for a few apps that I have been working on. I use FastCGI on shared hosts, but if I have a bit more control on a VPS or a dedicated server I prefer to use Mongrel since it is easier to install and configure and it is also more stable. Here is what I do to get a Mongrel cluster up and running using Capistrano and the extension that Jamis Buck also wrote named Multistage.

Make sure you have ruby, rails, capistrano, capistrano-ext, mongrel, palmtree and mongrel_cluster gems installed on your system.

To generate your cluster files you can run the following commands with your specific details of course. 😉

~ $ cd rails_app
~/rails_app $ mongrel_rails cluster::configure -e development -c "/home/www/apps/web2.0app.com" -p 8000 -N 4 -C config/mongrel_development.yaml
~/rails_app $ mongrel_rails cluster::configure -e staging -c "/home/www/apps/web2.0app.com" -p 8010 -N 4 -C config/mongrel_staging.yaml
~/rails_app $ mongrel_rails cluster::configure -e production -c "/home/www/apps/web2.0app.com" -p 8020 -N 4 -C config/mongrel_production.yaml

Now all you need to do is configure Capistrano config/deploy.rb file to make use of these cluster files and the Multistage extension for Capistrano. If you don’t how to setup Multistage, you can do a search for it or read my other post in it.

require 'palmtree/recipes/mongrel_cluster'
set :stages, %w(staging production development)
set :default_stage, "development"
require 'capistrano/ext/multistage'
...
set(:mongrel_conf) { "#{current_path}/config/mongrel_cluster.yml" }
...
deploy.task :after_update_code, :roles => [:web] do
  desc "Copying the right mongrel cluster config for the current stage environment."
  run "cp -f #{release_path}/config/mongrel_#{stage}.yml #{release_path}/config/mongrel_cluster.yml"
end

In order for the correct mongrel cluster to start you will need to have a recipe in your deploy that ensures that the correct cluster file is renamed to the config/mongrel_cluster.yml and then it is used by Capistranos’ mongrel:cluster:restart task.

Admittedly there are many more things that need to be done before and after this little tip, but I thought that this may help someone who may need to bridge their understanding of how easy it is to solve the Mongrel cluster on different stages problem.

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