Currently libprocess only supports gRPC client for unary gRPC calls through
MESOS-7749. To have full gRPC support to enable V1 gRPC API, we have to lay out the design for:
1. gRPC server support for unary gRPC calls.
2. gRPC server streaming support.
Optionally, we could consider support the following:
3. gRPC client streaming support. Only very few API calls use this so not as important as above.
4. gRPC bidirectional streaming support. Mesos API does not use this pattern currently.