Run server on multiple ports

[ST-DDT]

grpc/grpc-java#5067

Recently grpc-java added the ability to run a single server on multiple ports (Might be available with grpc 1.19). Should we add support for it in our library as well?

Example use cases might include:

• Use specific access roles based on the used server address. Address A is WWW-public, Address B is only accessible from within the network and thus can be used for privileged operations. (Accessible via Attributes with key TRANSPORT_ATTR_LOCAL_ADDR)

[ST-DDT]

grpc-java v1.19.0

[yidongnan]

Should we add support for it in our library as well?

+1

[ST-DDT]

This is mostly already possible with GrpcServerConfigurer and I want to rething my current design proposal some more, so I move this to the next version v2.5.0. Unless there's an objection

[ST-DDT]

Removed it from the 2.5.0 milestone.
I don't have a good feeling with implementing this just like this.
Waiting for an actual usecase.

[pluttrell]

I think that the originally proposed use case is pretty generic in scope and a very important one to support. If we want to segregate calls to certain APIs, for whatever underlying reason, it should be supported.

As for the underlying reasons, I can see a couple:

• Call Segregation. Some services provide APIs intended for both public and internal consumption. Limiting those intended for internal only consumption to a separate port maps nicely to how many traditional operators deploy services and block access. While it's advised to provide security beyond the network perimeter, not everyone will. And for those who do, it'll provide an additional level of protection knowing that the APIs aren't routable externally.

• Health Checks. If users deploy their APIs publicly, we shouldn't also force them to expose their health checks in the same way. Kubernetes for example can work beautifully with health checks provided on a separate port.