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Keeping capistrano in check: ensuring roles are respected in sub-tasks

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Bryan Liles

Posts: 228
Nickname: bryanl
Registered: May, 2008

Bryan Liles is the Principal Web Developer for Sourcefire, Inc.

Keeping capistrano in check: ensuring roles are respected in sub-tasks

Posted: May 20, 2008 8:36 PM

This post originated from an RSS feed registered with Ruby Buzz by Bryan Liles.
Original Post: Keeping capistrano in check: ensuring roles are respected in sub-tasks Feed Title: Smarticus Feed URL: http://smartic.us/feed/atom.xml Feed Description: Ramblings of a ruby hacker	Latest Ruby Buzz Posts Latest Ruby Buzz Posts by Bryan Liles Latest Posts From Smarticus

I’ve been knee deep in capistrano lately, and I’ve come across in interesting behavior:

Say you have the following:

 
role :app, "app"
role :web, "web"

task :run_on_web, :roles => :web do
  do_something_on_server
end

task :run_on_app, :roles => :app do
  do_something_on_server
end

task :do_something_on_server do
  run "/usr/sbin/something"
end

If you run the run_on_web task, it will execute the do_something_on_server task using all roles. This isn’t the behavior you most expected most likely. The secret to making this work is to set ENV[‘HOSTS’] match your the set of hosts you are interested in. After you are done you’ll want to set ENV[‘HOSTS’] hosts back to it’s original contents. I’ve whipped up a quick method to make this even easier.


def with_role(role, &block)
  original, ENV['HOSTS'] = ENV['HOSTS'], find_servers(:roles =>role).map{|d| d.host}.join(",")
  begin
    yield
  ensure
    ENV['HOSTS'] = original 
  end
end

You can call it like this:


role :app, "app"
role :web, "web"

task :run_on_web, :roles => :web do
  with_role :web do
    do_something_on_server
  end
end

task :run_on_app, :roles => :app do
  with_role :app do
    do_something_on_server
  end
end

task :do_something_on_server do
  run "/usr/sbin/something"
end

Hopefully this helps someone.

Read: Keeping capistrano in check: ensuring roles are respected in sub-tasks

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