Introduction to REST

The REST acronym stands for Representational State Transfer. It's an architectural style and a design for network-based software. It describes how one system can communicate a state with another. This fits perfectly well into the microservice world. As you will remember from Chapter 3, Working with Microservices, the software applications based on the microservices architecture is a bunch of separated, independent services talking to each other.

There are some concepts in REST that we need to understand, before we go further:

• resource: This is the main concept in the REST architecture. Any information can be a resource. A bank account, a person, an image, a book. A representation of a resource must be stateless
• representation: A specific way a resource can be represented. For example, a bank account resource can be represented using JSON, XML, or HTML. Different clients might request different representations of the resource, one can accept JSON, while others will be expecting XML
• server: A service provider. It exposes services which can be consumed by clients
• client: A service consumer. This could be another microservice, application, or just a user's web browser running an Angular application, for example

As the definition says, REST is being used to transport those resource representations over the network. The representation itself is being created via some media type. Media types can be different. Some examples of media types include JSON, XML, or RDF. The JSON media type is widely accepted and probably the most often used. In our examples, we will also use JSON to communicate with our service. Of course, REST is not the only option for microservices communication; there are others, such as Google's very good gRPC, for example, which brings a lot of advantages such as HTTP/2 and protobuff. In the REST architecture, resources are manipulated by components. In fact, these components are our microservices. Components request and manipulate resources via a standard uniform interface. REST is not tied to any specific protocol; however, REST calls are most often being made using the most popular HTTP or HTTPS protocol. In the case of HTTP, this uniform interface consists of standard HTTP methods such as GET, PUT, POST, and DELETE.

Before we start implementing our service that will respond to HTTP calls, it's worth knowing about the HTTP methods we are going to use. We are going to focus on them a little bit closer now.