gRPC is a popular framework for creating high-performance remote procedure call-based microservices.
OSGi Remote Services is a transport-agnostic specification for creating dynamic, versionable, modular, remote services.
The ECF project provides an open implementation of the OSGi Remote Services spec, and has a provider implementation based-upon gRPC. What this means is that gRPC can be used to create and run as an OSGi remote service, with all the support for service dynamics (particularly important for network-based services), versioning, and other features provided by OSGi remote services.
The architectural fit between gRPC and OSGi Remote Services is very good, since gRPC is concerned with transport-level efficiency (i.e. http/2, binary serialization format), and OSGi Remote Services are completely transport-agnostic, and focuses instead upon service-level concerns (e.g. dynamics, versioning, and service discovery).
gRPC offers support for server and client-based streaming. In ECF's implementation, streaming rpcs are mapped to the reactivex api. This means that consumers and implementers of a streaming rpc can simply call methods and provide callbacks (using Flowable), and non-blocking streaming calls will be made. In addition, the use of reactivex and backpressure will result in transport-level flow control for these streaming APIs!
Another advantage of gRPC for OSGi remote services is it's polyglot nature. This means that if (for example) a gRPC remote service is run as an OSGi/Java server, clients can be easily implemented in any of the languages supported by gRPC. As well, servers written in some other language can easily created and accessed from OSGi consumers. An example of this is the ECF etcd3 discovery provider, which communicates with an etcd server (written in Go) to publish and discover OSGi remote services.
Finally, with bndtools (an Eclipse plugin for OSGi bundle development), ECF Remote Service workspace template, and it's support for generating code as part of Eclipse's incremental build, gRPC code generation can be seemlessly integrated into the Eclipse development environment so that gRPC code generation, compile, and bundle packaging can happen immediately and continuously as part of gRPC remote service development. For a video tutorial demonstrating this, please see here.
