zuul-merger slows us down, we only have two instances (on contint1001 and contint2001). We should be able to easily add more to scale the merger operations. At first that can probably be done by collocating new instances with the servers, or maybe just use Ganeti VM.
Disk io might be a concern (git)
Instances have to be reachable from WMCS
There is a gotcha when provisioning a new one. Repositories might overlaps each other and prevent the initial git clones.