Chef: download a gem file and install it during compile phase.

default.rb

chef_gem "my_gem"
  source "#{Chef::Config[:file_cache_path]}/my.gem"
  # only do anything if we are notified
  action :nothing
end

remote_file "#{Chef::Config[:file_cache_path]}/my.gem" do
  source "http://example.com/my.gem"
  checksum "deadbeefdeadbeefdeadbeef"

  notifies :install, "chef_gem[my_gem]", :immediately
  action :nothing
end.run_action(:create)