Extension to https://github.com/engineyard/ey-cloud-recipes/tree/master/cookbooks/env_vars to enable custom unicorn config file as per https://support.cloud.engineyard.com/entries/20996656-Customize-Unicorn

default.rb

#
# Cookbook Name:: env_vars
# Recipe:: default
#

if ['solo', 'app', 'app_master', 'util'].include?(node[:instance_role])

  execute "reload-nginx" do
    action :nothing
    command "/etc/init.d/nginx reload"
  end

  node[:applications].each do |app_name, data|
    template "/data/#{app_name}/shared/config/env.custom" do
      source "env.custom.erb"
      owner node[:users].first[:username]
      group node[:users].first[:username]
      mode 0744
      variables({
          :app_name => app_name,
          :env_vars => node[:env_vars]
      })
    end

    case node[:environment][:stack]
    when /nginx_passenger/i
      template "/data/#{app_name}/shared/bin/ruby_wrapper" do
        source "ruby_wrapper.erb"
        owner node[:users].first[:username]
        group node[:users].first[:username]
        mode 0755
        variables({
            :app_name => app_name
        })
      end

      execute "update-nginx-passenger-ruby" do
        command "echo 'passenger_ruby /data/#{app_name}/shared/bin/ruby_wrapper;' >> /etc/nginx/stack.conf"
        not_if "grep passenger_ruby /etc/nginx/stack.conf"
        notifies :run, resources(:execute => "reload-nginx")
      end
    end

  end

end

env_vars.rb

# Specify environment variables for Unicorn or Passenger here
default[:env_vars] = {
  :UNICORN_CONF => "/data/#{@app_name}/shared/config/custom_unicorn.rb"
}