Rack::CacheBuster

Use to wind down a running app when needed.

Limits the max-age to the contents of the WIND_DOWN file, and salts the ETags to unsure clients see different deployments as having different contents.

Usage:

require "rack/cache_buster"
…
use Rack::CacheBuster, APP_VERSION, WIND_DOWN_TIME

Rails Usage:

require "rack/cache_buster"
…
use Rack::CacheBuster::Rails

Before you deploy (capistrano):

Add this to your deploy.rb:

begin
  gem "rack-cache-buster"
  require 'rack_cache_buster_recipes'
rescue LoadError
  puts "\n\n*** Please gem install rack-cache-buster before trying to deploy.\n\n"
end

# set :wind_down_time, 60*60 # defaults to 1hr

Then:

cap cache:winddown

… wait 1 hr …

cap deploy:migrations

… profit!

Before you deploy (other):

• Find the maximum cache duration for all pages in your app, start this process with at least that amount time before you deploy.

• Create a WIND_DOWN file in the app root of all your app servers.

• Restart all instances (touch tmp/restart.txt will be fine for passenger apps).

• Once all the caches should have expired you can deploy as normal.

Notes

If you are using Rack::Cache, you can safely put the CacheBuster below it in the stack, but only if you clear Rack::Cache's cache upon deploy.

This is actually the recommended approach as it will prevent the increased amount of hits between WIND_DOWN_TIME and your actual deployment from making it through to your app.