Introduction to gRPC

gRPC (Google Remote Procedure Call) is an open-source, high-performance RPC (Remote Procedure Call) framework initially developed by Google. It employs the efficient binary data format Protocol Buffers (Protobuf) to carry data and supports many languages, making it ideal for polyglot microservices architectures.

Table of Contents:

• What is gRPC?
• Terminology in gRPC
• Protocol Buffers and Proto Files
• Communication Modes in gRPC
• Use-cases for gRPC
• Conclusion

What is gRPC?

gRPC is a high-performance, open-source universal remote procedure call (RPC) framework. Google originally developed it, and the Cloud Native Computing Foundation maintains it. The acronym gRPC stands for Google Remote Procedure Call, reflecting its origins.

gRPC allows developers to define services and specify how their methods can be called, including details about the parameters and return types. gRPC is an excellent choice for designing consistent service-to-service communication and APIs.

Using Protobuf, the interface definition language (IDL), services, and message types are defined in .proto files. gRPC lets you write applications where a client application can invoke methods on a server application. The ability to directly invoke methods on a server makes it easier to create distributed applications and services.

Terminology in gRPC

Understanding gRPC necessitates familiarity with some key terms:

• Service: Defined in a .proto file, it’s a collection of RPCs that a client can call.
• RPC: Remote Procedure Call. A client invokes a method on a server.
• Message: Structured data is serialized using the protobuf data format.
• Channel: A logical connection to an endpoint. Channels are key abstractions for connecting to a gRPC service.
• Stub: A client-side representation of a gRPC service.

Protocol Buffers and Proto Files

Protocol Buffers, known as Protobuf, is Google’s language-neutral, platform-neutral, extensible mechanism for serializing structured data. For example, in gRPC, you define message types and services in a .proto file, then compile it using the Protobuf compiler protoc to generate data access classes in your chosen language. This mechanism is more efficient and faster compared to JSON or XML.

Here’s a basic example of a .proto file:

syntax = "proto3";

package helloworld;

service Greeter {
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

message HelloRequest {
  string name = 1;
}

message HelloReply {
  string message = 1;
}

The above code is a Protobuf service definition for a simple gRPC service. The syntax = "proto3"; instruction defines the syntax "proto3", the latest version of Protocol Buffers (Protobuf) language.

The definition starts with the package helloworld; declaration. Packages help to prevent name clashes between different services.

Next, a service called Greeter is defined. This service exposes a method named SayHello. The rpc keyword defines a remote procedure call (RPC) method. This SayHello method takes a single argument, HelloRequest, and returns a HelloReply. HelloRequest and HelloReply are message types defined in the same file.

The HelloRequest message type has a single field, name, of type string. The number 1 is the field number used to identify your fields in the binary message format.

Similarly, the HelloReply message type has a single field message of type string with field number 1.

In essence, this service accepts a request with a name and replies with a message. The service’s implementation will define the actual contents of the request and reply and the action the SayHello method takes.

Communication Modes in gRPC

gRPC supports four types of communication:

1. Unary RPC: The most common type, where the server returns a single response to the client request.
2. Server streaming RPC: The server returns a stream of responses to a single client request.
3. Client streaming RPC: The client sends the server a stream of messages.
4. Bidirectional streaming RPC: The client and server send messages using a read-write stream.

gRPC supports multiple communication patterns, such as unary (simple request-response), server streaming, client streaming, and bidirectional streaming. This makes it a versatile choice for various use cases.

Furthermore, gRPC uses HTTP/2 as its transport protocol, allowing for benefits like multiplexing, flow control, header compression, and the ability to send multiple amounts of data in both directions. It also supports various types of authentication, such as SSL/TLS and token-based authentication.

Use-cases for gRPC

gRPC is especially suited for the following scenarios:

• Microservices architectures: gRPC, with its support for multiple languages, is ideal for communication between services in a microservices architecture.
• Low latency, high throughput scenarios: gRPC’s Protobuf serialization and support for HTTP/2 make it a good choice for systems requiring low latency and high throughput.
• Point-to-point real-time communication: The different gRPC communication modes can effectively handle real-time communication.

Conclusion

gRPC is a robust, efficient, and versatile RPC framework. Its use of Protobuf and support for numerous languages and communication modes make it a valuable tool for many scenarios, especially in building scalable microservices. In addition, familiarizing yourself with gRPC concepts and mastering Protobuf can significantly boost your distributed systems.