The terms RESTful API and Microservices go hand-in-hand when building a microservices-based application. Nevertheless, they refer to very different things. The easiest way to understand the difference between RESTful APIs and microservices is like this:

  • Microservices: The individual services and functions – or building blocks – that form a larger microservices-based application.
  • RESTful APIs: The rules, routines, commands, and protocols – or  – that integrates the individual microservices, so they function as a single application.

What is a RESTful API?
Let’s start by defining “API” (application programming interface). An API is a defined set of rules, commands, permissions, or protocols that allow users and applications to interact with – and access data from – a specific application or microservice. When connecting microservices to create a microservices-based application, APIs define the rules that limit and permit certain actions, interactions, commands, and data-sharing between individual services.

The API is an interface, through which many developers interact with the data. A good designed API is always very easy to use and makes the developer’s life very smooth. API is the GUI for developers, if it is confusing or not verbose, then the developer will start finding the alternatives or stop using it. Developers’ experience is the most important metric to measure the quality of the APIs.

One of the most popular types of APIs for building microservices applications is known as “RESTful API” or “REST API.” REST API is a popular standard among developers because it uses HTTP commands, which most developers are familiar with and have an easy time using. Here are the defining characteristics of RESTful API:

An API that uses the REST (representational state transfer) model.
Relies on HTTP coding which is familiar to web developers.
Uses SSL (Secure Sockets Layer) encryption.
Language agnostic in that you can use to connect apps and microservices written in different programming languages.
REST APIs allow you to create a web application with CRUD operations (create, retrieve, update, delete).
The commands – or “verbs” – common to REST API include: 

Developers use these RESTful API commands to perform actions on different “resources” within an application or service. Those resources could be data in a database that pertains to employees, accounting details, medical records, or many other things. In addition to resources, RESTful APIs use URLs (Uniform Resource Locators), which allow you to locate and indicate the resource you want to perform an action on.

The familiarity and reliability of RESTful API commands, rules, and protocols make it easier to develop applications that integrate with applications that have an associated API. This is especially true when a company like Instagram, Twitter, Salesforce, or Facebook want to make their services available to integrate with third-party applications.

The Facebook Messenger Platform is an excellent example of RESTful APIs in action. Messenger is comprised of a variety of microservices – such as “Send” for sending messages and “Attachment” for attaching and sending files. To help third-party developers create applications that integrate with these and other messenger services, Facebook has published several RESTful APIs. 

The Messenger Platform provides a set of REST APIs that give you the tools you need to create awesome Messenger experiences. From sending rich messages, to finding your existing customers on Messenger, to customizing your bot and more, our APIs are the primary way you will work with the Messenger Platform.

Here are three REST APIs available for the Messenger Platform:

Send API: Serves as the primary way for apps to integrate with the Messenger Platform. The Send API allows developers to create third-party applications that log into an account on Facebook Messenger and send and receive text messages and file attachments. This allows developers to build auto-response bots, chatbots, and other services that integrate with the Messenger platform.
Attachment Upload API: Allows your app to upload and send images, audio, videos, and files through messenger. This API also makes uploaded assets reusable, so you don’t have to keep uploading files that you send repeatedly.
Messaging Insights API: Allows your app to retrieve Page Insights related to your Facebook page. This makes different Facebook metrics available to your app – particularly those related to conversation numbers, responsiveness, block rate, and more.
RESTful APIs for Facebook, Salesforce, and countless other cloud-based applications and microservices have empowered app developers to connect and integrate their applications with the widest array of platforms and services. This gives platform developers greater power, flexibility, extensibility, and reach – and it encourages innovation in ways the original platform developers may not have imagined.

What Are Microservices?
The best way to explain microservices – and microservices-based applications – is to start with a description of monolithic applications. 

Enterprises have long relied on monolithic applications to run their operations and provide different functions and services to their customers. All the code for a monolithic application’s services and functions is found within the same piece of programming.

Monolithic software is designed to be self-contained; components of the program are interconnected and interdependent rather than loosely coupled as is the case with modular software programs. In a tightly-coupled architecture, each component and its associated components must be present in order for code to be executed or compiled.

Furthermore, if any program component must be updated, the whole application has to be rewritten, whereas in a modular application, any separate module (such as a microservice) can be changed without affecting other parts of the program. 

A monolithic application architecture makes sense when an enterprise is first starting out, but eventually, enterprises will need to upgrade and scale their monoliths as their businesses and customer-bases grow. This can be challenging because the code for the monolith’s services and functions is tightly-coupled and highly interdependent. 

The more developers bolt new services and functions onto the monolith, the more difficult it becomes to untangle the code for future upgrades. Eventually, it’s virtually impossible to change even a small part of the monolith without refactoring the entire application. Moreover, scaling a monolithic application is also inefficient because developers have to scale the whole application – instead of simply scaling an individual function or service.

The upgrading and scaling challenges of monolithic applications eventually led developers to create the microservices-based application architecture. The microservices architectural style breaks the monolith into its component functions and services. Then it develops and runs each service as a small, autonomous, independent application, i.e., microservice. Finally, it loosely connects these microservices – usually with RESTful APIs – so they work together to form the larger application.

Microservices is the idea of offering a broader platform, application or service as a collection of combined services. These microservices provide specialized, fine-grained cooperation that makes up the more comprehensive architecture model.

The use of microservices in apps can be structured in many different ways. Within the application, a microservice does one defined job – for example, authenticating users, generating a particular data model or creating a particular report. The idea is that these microservices, which are often language-agnostic, can fit into any type of app and communicate or cooperate with each other to achieve the overall goal.