This was a for-fun project I did as a counterpart to a websocket based, asynchronous browser event distribution platform.
This implementation uses grpc streams and illustrates how to use the streaming server to do this. Since the gRPC call
for Subscribe is called in the gRPC code from a goroutine Subscribe has to capture that goroutine and hold the server
instance which can then deliver messages that come in out-of-band to the client. If Subscribe returns, the context
is closed.
This method is a bit cleaner and easier that the websocket design but undoubtedly uses more memory but not sure how much more or if that matters a ton. Sometimes the context closes well after a tab closes and depending on the browser, but it eventually does. Websocket version closes instantly on client hangup. In reality this would still need a side channel distribution network like redis or maybe RabbitMQ (AMQP).
Since we are using gRPC-web a proxy is required, so an Envoy instance is included but any proxy should work that supports gRPC-web.
brew install go-grpc protoc-gen-go-grpc protoc-gen-grpc-web
#In different terminals
make run-proxy
make run-server
make run-client
The main is set up to profile. Long story short is most of the memory is allocated in the Subscribe function where the client channel is allocated. I was able to serve 250K clients in under 1GB.
go tool pprof --pdf server/server server/profiles/<profile>.pprof > <profile>.pdf