Example of environment / URI driven database.yml

database.yml.erb

<%
  if ENV['DATABASE_URL']
    db_uri = URI.parse(ENV['DATABASE_URL'])  %>
production:
  adapter: <%= db_uri.scheme) %>
  database: <%= db_uri.path %>
  username: <%= db_uri.username %>
  <% if db_uri.password %>
  password: <%= db_uri.password %>
  <% end %>
  host: <%= db_uri.host %>
  <% if db_uri.port %>
  port: <%= db_uri.port %>
  <% end %>
<% else %>
production:
  adapter: mysql2
  database: XXX
  username: XXX
  password: XXX
  host: localhost
<% end %>