deployment_locking.rb

namespace :deployment do
  desc "Mark the deployment as locked, preventing further deployments (until deployment:unlock)"
  task :lock, :roles => :app do
    run "touch -f #{shared_path}/locked"
  end
  
  desc "Unmark the deployment as locked, allowing further deployments (until deployment:lock)"
  task :unlock, :roles => :app do
    run "rm #{shared_path}/locked"
  end
  
  task :abort_if_locked do
    run "if [ -f #{shared_path}/locked ]; then echo '***** THE PROJECT HAS BEEN LOCKED *****'; false; fi"
  end
end

before "deploy" do
  deployment.abort_if_locked
end