Bulk updating dozens of (not identical) servers

[Carlos A. Carnero Delgado]

Hi there,

the number of servers we have in my organization -- both physical and
virtual -- is slowly increasing at a steady pace, and the trend will
continue for the foreseeable future. It has come to the point that
apt-get upgrading && updating each one individually, and manually, is
really time consuming and prone to errors. We're looking into stuff
like Puppet and Cfengine, and it seems that either will do fine, but
we have this "feeling" or notion that they're a little bit heavyweight
for our needs. Not to mention the learning curve.

So, in the context of *only* dealing with installed packages updates
in an automated way[1] and having 8.04 and 10.04 LTS releases in
service, do you guys recommend anything? Did you write custom code?
Has anyone seen Fabric in the context of systems administration?

  [1] Please note that automated here really means "bulk updating" started
       from a command (or thingie) given by an administrator. It should not
       be interpreted as autonomously contacting repos.

Thanks in advance,
Carlos.