mw18 (at least) is missing the php5-memcached package:

reedy@fenari:~$ tail -n 1000 /home/wikipedia/syslog/apache.log | grep Memcached
Oct 31 15:36:14 10.0.11.18 apache2[21681]: PHP Fatal error: Class 'Memcached' not found in /usr/local/apache/common-local/php-1.21wmf3/includes/objectcache/MemcachedPeclBagOStuff.php on line 57
reedy@fenari:~$ ssh 10.0.11.18
Linux mw18 2.6.32-41-generic #89-Ubuntu SMP Fri Apr 27 22:18:56 UTC 2012 x86_64 GNU/Linux
Ubuntu 10.04.4 LTS

78 packages can be updated.
64 updates are security updates.

New release 'precise' available.
Run 'do-release-upgrade' to upgrade to it.

The last Puppet run was at Wed Oct 31 15:41:25 UTC 2012 (1 minutes ago).
reedy@mw18:~$ dpkg -l | grep memcached
ii memcached 1.4.2-1ubuntu3 A high-performance memory object caching sys
reedy@mw18:~$ logout
Connection to 10.0.11.18 closed.
reedy@fenari:~$ ssh 10.0.11.17
Linux mw17 2.6.32-33-server #72-Ubuntu SMP Fri Jul 29 21:21:55 UTC 2011 x86_64 GNU/Linux
Ubuntu 10.04.3 LTS

119 packages can be updated.
97 updates are security updates.

New release 'precise' available.
Run 'do-release-upgrade' to upgrade to it.

The last Puppet run was at Wed Oct 31 14:58:51 UTC 2012 (43 minutes ago).
reedy@mw17:~$ dpkg -l | grep memcached
ii libmemcached10 1.0.8-1~wmf+lucid1 C and C++ client library to the memcached se
ii memcached 1.4.2-1ubuntu4 A high-performance memory object caching sys
ii php5-memcached 2.1.0-2~wmf+lucid1 memcached extension module for PHP5, uses li

Going to have a look around and see if it's not anywhere else either...

Version: unspecified
Severity: normal