CFEngine: easy classification of mail reports

Once you have started to manage tens of servers with CFEngine (great!), if you stick to mail reports you will quickly become overwhelmed. To classify them more easily, here is a trick with CFEngine-3.6.

By default the subject is [fqdn/ip], for example (mail headers)

Subject: [debian70.boring/]

Not very easy to filter them through your email client (in case you don’t/can’t use a powerful MDA like procmail) without clashing with others similar subjects.

Here comes the mailsubject option of cf-execd, which allows you to set your own mail subject through body executor control. The cf-execd configuration lies in the /var/cfengine/inputs/controls/ file.

Example from the documentation:

 body executor control
        mailsubject => "CFEngine report ($(sys.fqhost))";

Which gives (mail headers):

Subject: CFEngine report (debian70.boring)

Easier to filter, easy to customize with all the CFEngine variables available, and a little undocumented bonus, an extra X-CFEngine: mail header is added when this option is set:

X-CFEngine: vfqhost="debian71.boring";ip-addresses=" fe80::a00:24fe:9eab:77ba";policyhub="";..."

But this time, no way to customize it.

There is a pull request to add this header even if mailsubject option is not set, if you are interested in, please add a comment to the GitHub entry!

Latest extra, the corresponding procmail rule:

* ^X-CFEngine:

Reporting through mail becomes more inefficient with the increase of managed servers. Consider logging through Syslog for better scalability, here is a great post about it.