Running the same command on many machines at once

A simple problem with so many self-scripted solutions is logging in to multiple boxes in parallel, executing the same command on every box at once. No matter whether you want to check the status of a certain service or look at some critical system data on all boxes, being able to log in to many servers in parallel can save you a lot of time and hassle (imagine forgetting one of your seven web servers when disabling the basic authentication for your website).

How to do it...

Let's try to execute a few simple commands on multiple servers in parallel:

1. Retrieve the status of the nginx processes from all your web servers (assuming you have at least one host up and running, which has the role web_server):

   mma@laptop:~/chef-repo $ knife ssh 'role:web_server' 'sudo sv status nginx'
   

   www1.prod.example.com run: nginx: (pid 12356) 204667s; run: log: (pid 1135) 912026s
   www2.prod.example.com run: nginx: (pid 19155) 199923s; run: log: (pid 1138) 834124s
   www...