gRPC - General Purpose Remote Procedure Call

Google has developed gRPC in 2015 and released it for the world to use. gRPC has been evolved from Stubby,  which Google has been using for all internal communication. 

gRPC is open-sourced high-performance RPC framework. It efficiently connects services across machines with pluggable support for load balancing, authentication, monitoring. It supports a wide range of programming language and it can be developed and deployed fast. Microservices architecture does support gRPC communication over service mesh and pretty efficient over REST. 

• Client libraries in 10 programming languages. gRPC Languages
• Bidirectional streaming and http/2 supported.
• pluggable load balancing, auth and monitoring. 
• Request response and streaming support are available.
• Strongly typed message definition using Protobuf. 

gRPC work like a client-server model. The client will call the framework generated stub (client) to make a service request on a different machine. The server will take the request, execute the service code to handle the request and send back the response object. All this data comes in binary coded and proven to be efficient. 

Reference: grpc.io

gRPC uses IDL (interface definition language) using protobuf. Protobub is Google developed serializing framework.  Check here protocol-buffers. A .proto file will be generated to define message and service. Once generated we need to generate server and client code in our preferred language using protoc compiler. Compilers will generate client stub and server code in your prefered language and you can define service from there. 

Sample greeting.proto file 

// The greeter service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

Implementation Types:

1. Unary RPC

This work like a simple client request-response model. The client sends a request and server send the response and closes the RPC call. 

  rpc SayHello (HelloRequest) returns (HelloReply) {}




2. Server Streaming RPC

The client sends a request and the server will send a list of responses. The server will end the RPC call with metadata. Order of response will be maintained for a single RPC call. 

  rpc ListofHelloReplies(HelloRequest) returns (stream HelloReply) {}




3. Client Streaming RPC

The client will be sending multiple request messages to the server and once requests are exhausted, the server will be sending a single response for it. 

  rpc ListofHelloMessages (stream HelloRequest) returns (HelloReply) {}




4. Bidirectional streaming RPC

The client will be sending multiple request messages to the server and the server can choose to start responding or it can wait for all the request. In response to a series of request, the server will also be sending a series of response messages. 

  rpc BidirectionHelloMessageandReply (stream HelloRequest) returns (stream HelloReply) {}




Synchronous and Asynchronous: A service request call wait for the response and does nothing is an asynchronous call. An asynchronous call, the client will not be waiting for the response and will start working on other calls. Both the flavours can be implemented based on the requirement.