Microservices vs API – What is the Difference?

Marlena Walburg
Microservices vs API - What is the Difference?

APIs and microservices are very important in software development today. Nevertheless, they may sound a bit mysterious to the uninitiated. Some people, in turn, sometimes confuse these concepts, and there are specific reasons for this, which we will explain soon. When planning the development of a custom application, it is good to know these concepts, recognize the differences between microservices and APIs and their use cases. A better understanding of how the application that you are developing works is extremely relevant to your business and delivering value.

What are microservices?

Microservices is a type of service-oriented architecture structural style that organizes an application as a collection of individual services. The microservices architecture is characterized by certain service attributes such as organization around business opportunities, independent deployment and development using different technologies depending on the best solution, small size, messaging, context-limited and decentralized, and fine-grained.

Microservices are most often compared to monolithic architecture, which is the default approach to building an application. It assumes that the application is a single and indivisible entity, has one large codebase, and no single modules. Microservices, on the other hand, are distinguished by flexibility. Instead of a single, monolithic code, they propose to build the application as a set of services. In this architecture, all functionality is divided into independently deployable modules that communicate with each other using defined methods called APIs. Each service has its scope and can be updated, deployed and scaled independently of the others.

What is an API?

API stands for the application programming interface. It is a set of rules that strictly describes how programs communicate with each other and determines the interactions between multiple software intermediaries. An API is a set of specially defined methods of communication between different components. It explains the kinds of connections or requests that can be made and how to perform them. It is defined at the source code level for software components – libraries, applications, etc. The task of the API is to provide the relevant specifications of subroutines, data structures, object classes and the required communication protocols. Modern APIs adhere to standards such as HTTP and REST, which are very widely used and available. They are more standardized, have much stronger security and management discipline, and are monitored and managed for efficiency and size.

What is the difference between Microservices and API?

Microservices and APIs are often stacked and confused with each other. The main reason for it is that APIs are an essential part of microservices architecture. Both concepts deal with the structure and interaction of software. Microservices are sometimes misinterpreted as an endpoint that provides an API. However, microservices have much more flexibility and capabilities. Each of them will have its API. The API sits in front of the microservice and allows various components of that architecture to communicate with each other. Individually, microservices can draw on their functions to have a more controlled operation. It can be simply said that microservices are a whole, complex architecture, and APIs are one of its elements.

What are APIs used for?

The specificity of the API allows developers to interact with the application. Broadly speaking, APIs allow internal and external developers to access application data or use its features. This is how applications or websites are connected to communicate and collaborate. Thanks to APIs, it is possible to perform several different actions that you do not even think about – using a social account, accessing the map from another application, displaying widgets on the home screen, etc. Technically, APIs usually work by sending data via HTTP requests. They return a message, usually in JSON format, which developers use as needed. API design style types include REST, SOAP, GraphQL, and more. The growing popularity of microservices has led to an increasing number of private APIs as a lightweight solution for creating a communication framework for individual microservices. In building an application, an API simplifies programming by extracting the underlying implementation and providing only the objects or actions that the developer needs.

What are REST APIs? 

Let’s start with explaining what REST itself is. Representative state transfer (REST) ​​is a software architecture style that uses a subset of the HTTP protocol. It is commonly used to create interactive applications that use web services. A web service that follows these guidelines is called RESTful. Such a web service must expose its web resources in text form and be readable and modifiable through a stateless protocol and a predefined set of operations. This approach enables interoperability between the computer systems on the Internet that provide these services. REST was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation. By using a stateless protocol and standard operations, RESTful systems aim at rapid performance, reliability, and development capability by reusing components that can be managed and updated without affecting the system as a whole, even while it is running.

Hence, REST API is a universal HTTP interface for communication between client software and server over the network. REST APIs are currently the most popular type of API for cross-platform integrations and are also used in microservices. Web service APIs that conform to REST architectural constraints are called RESTful APIs. REST defines a set of restrictions on creating APIs that make them safe and efficient. REST APIs work by filling HTTP requests and returning the response in JSON format. HTTP is the standard protocol for transferring data over the network.

Can a Microservice have multiple APIs?

Microservices assume a specific architectural approach that divides individual application functions (services) into modular, stand-alone programs. While microservices and APIs are not the same, they are connected in some way by using APIs to communicate with each other. Just like an application uses a public API to integrate with another application, one microservice component uses a private API to access another component of the same microservice. Within a microservice, each service has its own API that determines what requests it can receive and how it responds. These APIs typically follow REST policies.

Is API gateway a Microservice?

API Gateway is a kind of entry point. Its role is to separate the rest of microservices from issues related to handling inquiries from client applications, so it will redirect inquiries from the client to the appropriate services. API Gateway is like the entrance door to the system and is not a microservice itself. However, API gateways are used in microservice-based applications to facilitate access to individual services.

How do I test the Microservices API?

In many ways, testing a microservice application is no different from testing an application built with any other architecture. However, the challenge with microservices is the sheer number of services that make up the application, along with the number of dependencies between the services. The most important thing is to define a thoughtful testing strategy that includes functional and non-functional testing, adherence to QA best practices and selecting the right team.

How do API gateways work?

An API Gateway is an API management tool that sits between the client and the set of backend services. It accepts all API calls from clients and then routes them to the appropriate microservice with request routing, composition, and protocol translation. It typically handles the request by invoking multiple microservices and aggregating the results to determine the best path. API gateways often handle common tasks used throughout the API service system, such as user authentication and statistics.

Which API Gateway is best for Microservices?

There are quite a few important players that offer API Gateways. Which one to choose will largely depend on your design needs, budget, etc. Take a look at a few of the most recognizable ones.


The first proposed API gateway, Kong, is open source and based on NGINX, the popular HTTP proxy. While the core functionality is open source, many features such as the admin interface, developer portal, and security are only available with an enterprise license. Out of the box, Kong provides many of the expected API Management features. It is modern, designed to manage microservices, has moderate implementation complexity and wide possibilities.

Amazon AWS API Gateway

Amazon AWS is the largest cloud provider and also offers AWS API Gateway. AWS API Gateway is fully managed and can be very quickly deployed on the AWS portal. Functionally, it is comparable to Kong but a little less recognizable and can be deployed solely on the cloud. It has many solutions that support building microservice platforms. 

Azure API Gateway

Azure API Gateway is another solution that is quite similar to the Amazon solution. It offers various payment plans with customized features like autoscaling, WebSocket and HTTP / 2 protocol traffic, multi-site hosting, etc. Like the previous options, it facilitates and supports the creation of microservices.

Do Microservices have to be RESTful?

REST APIs are often a good option for microservices-based applications because communication between microservices and client applications has to be fast with little network latency. If a microservice has a real need to respond synchronously, or if it needs to receive a response itself synchronously, then REST might be a good approach. However, the decision depends mostly on the requirements of the software you want to develop. Moreover, developing a microservices-based platform requires a lot of experience to be well-optimized, secure and efficient. Hence, have in mind that not only choosing a type of API for your microservices-based software is a challenge, and you will need real experts to develop it.


We hope that now you understand a little better what APIs and microservices are and how they work together. Microservices have been adopted by many global companies such as Netflix or Spotify, which is why familiarizing yourself with their concept is even more important from a business point of view.

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