A lesson I learnt today is: use promisees in cfengine promises, and you won’t regret it. In fact, I had a proof today that specifying a promisee is a very useful thing.

Let’s take a step back: a promisee is introduced by a -> sign, and according to the documentation the promisee is the abstract object to whom the promise is made. When CFEngine made its way in our trouble ticket, I started including a ticket number as a promisee every time a promise was created to address a reported issue.

Today I found out that, every time I deployed a change that caused firewall rules to be reloaded, ntpd was also restarted. I couldn’t understand why, so I checked the policies and found this:

      "/etc/init.d/ntp" -> "CLO-2313"
	  args       => "restart",
          ifvarclass => "ntp",
	  comment    => "Restart ntpd when the firewall is restarted" ;

CLO-2313 was a resolved ticket, and there I found out why I made such a decision more than one month ago, and why it was a good thing.

So… use promisees!