Introduction

What is Goa?

Goa is a Go framework for writing microservices that promotes best practice by providing a single source of truth from which server code, client code, and documentation is derived. The code generated by Goa follows the clean architecture pattern where composable modules are generated for the transport, endpoint, and business logic layers. The Goa package contains middleware, plugins, and other complementary functionality that can be leveraged in tandem with the generated code to implement complete microservices in an efficient manner. By using goa for developing microservices, implementers don’t have to worry about the documentation getting out of sync as Goa takes care of generating OpenAPI specifications for HTTP based services and gRPC protocol buffer files for gRPC based services (or both if the service supports both transports). Reviewers and consumers can also rest assured that the implementation follows the documentation as the code is generated from the same source.

Separation of Concerns

The DSL in goa v2 makes it possible to describe the services in a transport agnostic way. The service methods DSLs each describe the method input and output types. Transport specific DSL then describe how the method input is built from incoming data and how the output is serialized. For example, a method may specify that it accepts an object composed of two fields as input then the HTTP specific DSL may specify that one of the attributes is read from the incoming request headers while the others from the request body.

This clean decoupling means that the same service implementation can expose endpoints accessible via multiple transports such as HTTP or gRPC. Goa takes care of generating all the transport specific code including encoding, decoding and validations. User code only has to focus on the actual service method implementations.

Basic Data Types

The primitive types include Int, Int32, Int64, UInt UInt32, UInt64, Float32, Float64 and Bytes. This makes it possible to support transports such as gRPC but also makes HTTP interface definitions crisper than what JSON allows for.

Composable Code Generation

Code generation now follows a 2-phase process where the first phase produces a set of writers each exposing templates that can be further modified before running the last phase which generates the final artifacts. This makes it possible for plugins to alter the code generated by the built-in code generators.

How is Goa v2 different from v1?

• Goa v2 is composable. The package, code generation algorithms, and generated code are all more modular and make fewer assumptions than Goa v1 did.
• A microservice designed by Goa v2 is transport-agnostic. The decoupling of transport layer from the actual service implementation means that the same service can expose endpoints accessible via multiple transports such as HTTP and/or gRPC. Goa v2 takes care of generating all the transport-specific code including encoding, decoding, and validating requests and responses. Goa v1 produces code for HTTP transport only.
• The generated code follows a strict separation of concern where the actual service implmentation is isolated from the transport code. User code only has to focus on the actual service method implementations.
• Goa v2 generates code that relies mostly on Go standard library types making it easier to interface with external code.
• The goa-kit plugin makes it possible to generate go-kit microservices from Goa designs.