Having cross-datacenter consistency between WANObjectCache objects is one of the prerequisites for being able to serve MediaWiki from multiple datacenters.
This means basically substituting the current twemproxy solution for aggregating multiple memcached instances in a single cluster with a software that allows to broadcast/replicate writes
To this end, we want to use Facebook's mcrouter T156938
We have debian packages built, and a basic module that supports a single-datacenter installation in deployment-prep. The production installation, though, will need some work on our end.
Specifically, we need to figure out a suitable architecture for cross-dc to work, add proper monitoring of the software, and execute the transition from twemproxy to mcrouter in a secure way.