In gRPC, a unary RPC is the simplest and most common pattern for remote communication. With unary RPCs, a client sends a single request message to the server and receives a single response message in return. This one-to-one interaction closely resembles a typical function call, making it easy to understand and implement.

When you use unary RPCs, the client constructs a request object containing all necessary input data and sends it to the server. The server receives the request, processes it—often by performing business logic, querying a database, or invoking other services—and then returns a response object. Both the request and response are strongly typed, defined in advance using Protocol Buffers, which ensures clear contracts and minimizes errors.

The workflow for implementing a unary RPC in a gRPC service involves several practical steps. First, you define the service and its methods in a .proto file, specifying the request and response message types. After generating code from this definition, you implement the server-side logic by writing a method that takes a request object and returns a response. On the client side, you call the method as if it were a local function, passing the request data and handling the response.

Unary RPCs are widely used for operations such as retrieving a specific record, creating a new resource, or executing a calculation where a single response suffices. This pattern is efficient and straightforward, allowing you to build reliable, high-performance APIs that are easy to reason about and maintain.