Capistrano: How can I trigger a task on ALL hosts if ANY of them is failing a check?

Question

I am using capistrano to deploy a rails application.

I have a challenge of running a check across ALL hosts and then determining if a task should be triggered on ALL hosts, if ANY of them fails the check. The check could e.g. be looking for a file:

desc "Make sure file is on all servers"
  task :do_something do
    on roles(:app) do
      unless test("[ -f /some_dir/the_file.txt ]")
        # Run something on ALL servers if missing on just one of them...
      end
    end
  end
end

I have also considered if it could somehow be done by first running one task on all servers and combining up the result of those and then in a second task run it if the output of the first had the file missing on any of the servers.

Answer 1

I figured it:

task :check_something do
  has_file = []
  on roles(:app) do
    has_file << test("[ -f /some_dir/the_file.txt ]")
  end
  set(:should_run_something, has_file.any?{|file| file == false})
end

task :run_something do
  on roles(:app) do
    if fetch(:should_run_something)
      # Run my command
    end
  end
end
after :check_something, :run_something