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Golang / GoLang System Architecture and Testing Interview Questions

Compare REST/JSON with gRPC/Protocol Buffers. When would you choose gRPC for a Go microservice?

REST and gRPC solve the same problem — remote procedure calls — but make very different trade-offs. Understanding these trade-offs is central to microservice architecture decisions.

REST/JSON vs gRPC/Protobuf
AspectREST / JSONgRPC / Protobuf
ProtocolHTTP/1.1 or HTTP/2HTTP/2 (mandatory)
SerialisationJSON: text, ~30 bytes/field, human-readableProtobuf: binary, ~3-5 bytes/field, 5-10× smaller
SchemaOptional (OpenAPI), not enforced at compile timeRequired (.proto file), compile-time checked
Code generationOptionalRequired (protoc + language plugins)
Browser supportNativeNeeds grpc-web proxy layer
StreamingWorkarounds: SSE, WebSocketsBuilt-in: unary, server, client, bidirectional
LatencyHigher (text parsing overhead)Lower (binary + HTTP/2 multiplexing)
Best forPublic APIs, browser clients, simple integrationsInternal service-to-service, high-throughput, typed contracts
// user.proto
syntax = "proto3";
package user;

service UserService {
    rpc GetUser(GetUserRequest) returns (User);           // unary
    rpc StreamUsers(Empty) returns (stream User);         // server streaming
    rpc BatchCreate(stream CreateUserRequest)             // client streaming
        returns (BatchCreateResponse);
    rpc Chat(stream Message) returns (stream Message);    // bidirectional
}

message GetUserRequest { int64 id = 1; }
message User {
    int64  id    = 1;
    string name  = 2;
    string email = 3;
}

// Generate Go code:
// protoc --go_out=. --go-grpc_out=. user.proto

Why Go excels at gRPC: Go's goroutine model maps naturally to gRPC's concurrent streaming model. Each RPC handler runs in its own goroutine; the Go runtime multiplexes thousands of concurrent streams efficiently. Protobuf's generated Go code is idiomatic and integrates with Go's type system. Go's standard net/http and context packages align with gRPC's design.

Decision guide: choose gRPC for internal service-to-service calls where typed contracts, performance, and streaming matter. Use REST/JSON for public APIs consumed by browsers or third parties where human readability and broad tooling matter.

What serialisation format does gRPC use and what is its primary advantage over JSON?
Which gRPC streaming mode allows both the client and server to send multiple messages on a single connection?

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