What’s the Difference Between Microservices and APIs?

What’s the Difference Between Microservices and APIs?

Microservices and APIs are two approaches to modular software design. Modular programming aims to design smaller software components that interact with each other to perform complex functions. This is more efficient than designing software as one large codebase for all functions. Microservices are an architectural approach that composes software into small, independent, highly specialized services. Each microservice solves a single problem or performs a specific task. 

In contrast, an API is a contract of communication between two software components. APIs specify the data that the software component needs to perform a function, as well as the expected response. Microservices communicate with each other using APIs. However, developers also use third-party APIs to integrate preexisting functionality into their code.

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How they work: microservices vs. APIs

A microservice contains all the code required for a particular application function. An API is a communication mechanism to access that function. Microservices expose functionality via APIs so other microservices can use them when required. However, developers also use APIs unrelated to microservices, such as APIs from third-party vendors and partners.

Next, we detail how both of them work.

How microservices work

Microservice architecture is the evolution of the service-oriented architecture (SOA). Developers decompose an entire application into individual functions that run as small, standalone programs. The microservices interact with each other to perform more complex tasks.

For example, a ridesharing app could have multiple loosely coupled services, such as ones that retrieve geolocational data, process payments, or send alerts. When a user hails a ride on the app, all the microservices would work together to help the user find a driver and make the payment.

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How APIs work

APIs are an interface that allow any two software components to exchange information. An API specifies the communication contract. Developers use the contract to access specific functionality or data from third-party code.

For example, a ridesharing app could use a payment API by passing customer credit card details to the API. The code behind the API could securely deduct the payment from the card and return a success or failure response to the ridesharing app.

Key differences: microservices vs. APIs

Both microservices and APIs are important tech stacks that help organizations build and scale applications. Microservices are the building blocks of an application. Each service usually contains a database, data access layer, business logic, and API. APIs include programming details such as data format, data exchange expectations, and protocols. 

They support distributed development in different ways. 


The microservices architecture aims to improve software development efficiency by splitting a large code block into multiple smaller services. This way, several developers can work on different microservices simultaneously based on agreed specifications.

The API, meanwhile, connects different functions or services within or beyond an application. The scope of internal APIs is limited to a single application. Meanwhile, a public API can be used to access open-source functionality regardless of which programming languages and tools they were built on. 


Microservices are broadly categorized into stateful and stateless. Stateful microservices remember their past results when they process current requests, while stateless microservices don't retain past memories.

Meanwhile, APIs are categorized by audience, architecture, and protocol. For example, developers use the following types of APIs when they build applications: private, public, partner, microservices, composite, SOAP, and REST APIs.


Microservices provide you with more control over data security and availability, as they are developed and managed by your internal team.

Meanwhile, APIs may or may not be secure depending on who writes the code behind them and what data they ask for. Therefore, developers must be cautious when they use external APIs.


Microservices are difficult to debug because of their distributed architectural style. Moreover, individual microservices might be developed with different programming languages and frameworks and interact in an unpredictable pattern. This complicates the developer's efforts to reproduce the error state, track data movement, monitor programming variables, and identify the root cause.

Unlike the microservices architecture, it’s more straightforward to debug APIs. Developers can take a step-by-step approach to observe the API behavior and identify the root problem. 

When to use microservices vs. APIs

Microservices and APIs are not competing technologies. Instead, both work together to turn business logic into scalable modern applications that meet customer demands. 

Microservices need an API to expose certain functionalities to interact and exchange data with third-party services. With APIs, microservices can share data and help organizations scale applications rapidly.

Combining microservices and APIs is the right choice when a single codebase has become too complex for your team. By switching to a distributed architecture, you can save time and cost when you introduce new features or changes to your applications. 

Challenges at scale: microservices vs. APIs

Both APIs and microservices allow organizations to scale their applications more effectively than traditional software architecture. However, there are still challenges that APIs and microservices face as traffic and application complexity increases.

Eventually, developers must manage, monitor, and troubleshoot thousands of microservices and the APIs they use. They must deploy microservices with the appropriate infrastructure for code maintenance and agile change management.

Managing microservices at scale

Software developers deploy microservices with containers to overcome scalability challenges. Containers are software packages that contain all the resources and the operating environment a microservice needs. Containerization allows microservices to run independently from hardware and operating systems. You can allocate or reduce compute resources to specific microservices to meet changing demands. 

Managing APIs at scale

APIs might experience bottlenecks when they accept too many concurrent API calls. This overwhelms the API server, which causes performance issues and returns error codes to the sender application.

If you use third-party APIs, your application’s performance can be affected by the performance of code that you don’t manage. However, if you use internal APIs, you can use API management tools to monitor and secure multiple APIs at scale.

Summary of differences: microservices vs. APIs





Divide a large application into smaller functional components.

Define a communication contract between two software components.


A microservice contains all the code required for a particular application function. 

An API is communication mechanism to access that function. 


Stateful and stateless microservices.

Categorized by audience, architecture, and protocol.


Controlled internally. Fault-tolerant architecture.

May be dependent on third-party developers.


Challenging because of distributed architecture and complex data path.

Predictable approach to observe, track, and isolate issues.


Use containers to manage at scale.

Use API management tools to manage at scale.

How can AWS help with your microservices and API requirements?

Amazon Web Services (AWS) provides affordable and efficient solutions for deploying, managing, and securing microservices and APIs in the cloud. Organizations use AWS technologies to shift from conventional software architecture and embrace modern web applications. Here are two examples:

With Amazon Elastic Container Service (Amazon ECS), you can easily deploy, manage, and scale microservices-based applications on the cloud. It automatically provisions the underlying infrastructure and connects your application to other AWS resources. 

Amazon API Gateway provides a centralized platform that helps you to build, deploy, maintain, and secure APIs at scale. It allows APIs to send and respond to requests to a particular service with minimum latency and error rates.

Get started with microservices and APIs on AWS by creating an account today.