how-to? datacenter link break and resume

[justanyone]

Hello! Question about broken replication that is then fixed:

We have 2 datacenters. Our (sharded) data is replicated across them.
If we have a broken data center link, I want both databases (the
primary and the secondary) to remain writable - they would both think
that they are primary, so I can write. to both. This is fine in our
schema; inserts and updates are operating on disparate records/
documents.

But, what happens when the data link between the data centers
returns? Mongo should sync up again and declare one of them the
primary and we continue as normal.

Is this possible in a sort-of-normal deployment, or do I have to
custom script something?

Thanks in advance,
-- Kevin Rice

[A. Jesse Jiryu Davis]

This is not possible: Mongo is designed never to allow multiple primaries in a replica set, and only primaries are writable.