DSH stands for dancer's shell / distributed shell and is a way to run commands via SSH on many hosts at once.
Since agent forwarding was disabled, this is more of a pain. However, deployers can use:
SSH_AUTH_SOCK=/run/keyholder/proxy.sock dsh -F 20 -M -g mediawiki-installation -r ssh -o -oUser=mwdeploy -- [command]
From a deployment server, to run a command on all MediaWiki boxes.