gRPC is a great, but has a ton of small problems including a catastrophic documentation (in some cases we had to read byte code to figure out what to do).

The biggest issue for us was however was that there is no middle server that could handle an route connections to available workers. We were using haproxy which worked ok but far from great. It was very hard to figure out how many servers need to run at any given point and thus a ton of our requests were ending up with UNAVAILABLE response.

Essentially what we needed is a synchronous RPC over PubSub which gRPC doesn't offer.