It occurred to me that many Rails/Passenger/Apache applications may have caching set up in a way that it appears to be caching, when it is not actually caching.

Specify these gem versions in your Gemfile:

gem 'cucumber', '~> 1.3.0'
gem 'cucumber-rails', '= 0.3.2' # max version for Rails 2
gem 'capybara', '< 2' # capybara 2+ requires Rails 3
gem 'mime-types', '< 2' # dependeny of capybara

...

There are a bunch of basic functional elements to building out a popular Rails app that I've never really seen explained in one place, but we had to learn the hard way while building Posterous.

Learn everything you need to know about Scaling your Rails app through 13 informative Screencasts produced by Gregg Pollack with the support of New Relic.

dusen 0.4.8 and edge_rider 0.2.3 no longer depend on Rails (they still depend on ActiveRecord). That means you can use them e.g. with Sinatra.

Recently, we had an interesting lunch-break with the rails 3.1. asset-pipeline in production mode. Daniel Zahn made a blogpost about our journey, precompiling assets, fingerprinting, Haml, Sass & Compass and what he calls "the dark heinous hutch".

Expiration of Rails sessions

By default Rails sessions expire when the user closes her browser window.

To change this edit your config/initializers/session_store.rb like this:

ActionController::Base.session = ...

Proxy caching is a good feature to serve your publicly visible application content faster and reduce load on your servers. It is e.g. available in nginx, but also affects proxies delivered by ISPs.

Unfortunately, there is a little problem in Rail...

Find conditions for scopes can be given either as an array (:conditions => ['state = ?', 'draft']) or a hash (:conditions => { 'state' => 'draft' }). The later is nicer to read, but has horrible security implications in some versions of Ru...

General

Programatically invoke Rails generators
: Require the generator, instantiate it and invoke it (because generators are Thor::Groups, you need to invoke them with invoke_all). Example:

    require 'generators/wheelie/haml/...