Ruby on rails application with daily db:migrate:rebuild

Question

We have a ruby on rails app with a postgres database. As the data is ever changing we need to run a daily db:migrate:rebuild.

Currently when we run these tasks the site is taken down for a number of hours, and the passenger queue fills up on the server which takes down the other apps on the server. Looking for the most cost effective way of resolving this

My plan to stop this is to

• Create a secondary database server
• Configure a postgres replication from the master to the secondary slave.
• Configure the db:migrate:rebuild to run on the slave server
• Replicate the new db back to a new database on the master server, and update the database.yml file to point to the new database
• Restart nginx

A few questions:

How easy is it to configure the db:migrate to happen on the other db server? Do I just create a new rails environment called for example replica with the database details in? Then run

RAILS_ENV=replica bundle exec db:migrate:rebuild

Also will this still cause the passenger queue to fill up still?

Trying to avoid horizontal scaling of the web servers etc, as budget is still limited.

Here is the rake task definition:-

namespace :db do
namespace :migrate do
 desc "Run custom sql scripts"
 task :sql => :environment do
   ['helpers', 'mviews', 'plpgsql'].each do |dir|
     files = Dir.glob(Rails.root.join("db/#{dir}/*.sql"))
     files.sort.each do |file|
       puts file
       ActiveRecord::Base.connection.execute(File.read(file))
     end
   end
 end
 desc "Rebuild all computed values"
 task :rebuild => :migrate do
   Sapi.rebuild
 end
 end

Thanks!