In this article, we’ll cover the key differences between APIs and microservices as answered by our contributors consisting of senior decision-makers and CTOs from technology companies around the world.

APIs Defined

One of the most popular ways to consume data from a web service is through a web application programming interface (API). By interface, we are referring to an agreement, or schema, that anyone using this API must abide by.

Tools such as Swagger can be used to generate documentation from your APIs schema, which can then be shared by other third-party applications for improved interoperability.

By defining what is and is not acceptable, we avoid nasty bugs and exploits caused by misuse.

A web API is one of many inter-process communication (IPC) strategies used for communicating between systems or to handle requests from the internet.

Typically, modern web APIs follow the RESTful architectural design style that is loosely based on HTTP methods.

Erik Wilde, Digital Transformation Catalyst & leading API implementation at Axway provides helpful clarification on APIs in his comment below:

“An API is an agreement that provides direction for a consumer to use the service.”
“At a fundamental level, APIs can be compared to languages: It’s a communications mechanism that allows applications to communicate.”
“Much of the value of APIs is based on this “language nature” of APIs: If the only thing that two applications need to collaborate is to agree on a language, then there is much more freedom for these components than in more tightly coupled scenarios, where agreement may also cover aspects of how applications are implemented, or where they are run.
“The “API language” is designed by developers and consumed by developers.”
“Basically, an API serves as a contract for interactions within the microservices, allowing interaction between the two.”

Microservices Defined

Microservices may choose to use APIs as their choice of IPC, but they also serve a far greater role in software design.

As applications grow in complexity, technical debt begins to grow with it. As more features are added, the codebase becomes what is referred to as a “big ball of mud”, which makes the application difficult to maintain and adapt.

Monolithic applications such as these are fragile; if a fatal bug occurs, causing your application to restart or become unresponsive, the business risk can be huge.

Microservice architecture (MSA) attempts to solve this problem by breaking down your monolithic application’s logic into small chunks (i.e. services).

If a bug occurs in one microservice, you don’t lose the entire functionality of your application. For example, if your shopping cart microservice were to fail, customers can still browse products by interacting with the product catalogue microservice.

The only downside to MSA is that it requires more careful design considerations, such as how to fulfil requests that require the cooperation of multiple microservices, or what IPC best suits a given use-case.

Different microservices tend to require different levels of resources, such as memory usage and CPU power.

By breaking down functionality into multiple microservices, you are able to deploy them separately and allocate resources more efficiently.

Load balancing can also be controlled on a per-microservice basis for improved scalability. Some microservices will receive far greater levels of network traffic than others or play a more critical role in your business, and so these will need to distribute the workload between more worker nodes.

Erik also provides feedback on the core attributes of microservices, he continues:

“Microservices are a design that are separated into quantities of a usually large application into smaller, independent services.”
“An API is an agreement that provides direction for a consumer to use the service. Microservices serve more than just being an API for a system.”
“An entire application can embody a sequence of microservices that use their own APIs for interacting with one another.”
“Furthermore, microservices individually are able to draw from their own functions to have a more controllable operation.”
“Early service-oriented architecture allowed access to monoliths (large codebases with very complex release and deployment dances) via SOAP, providing value through API access, but did nothing about the tightly coupled code.”
“Microservices are simply service-oriented architecture done right: as decoupled implementations.”

Microservices vs APIs: The Key Differences

Kin Lane, Chief Evangelist at Postman summarised the main top-level difference between these services in his response;

“Microservices are an organizational-wide architectural style-defining how teams will design and deliver application infrastructure as a set of small, single-purpose web services that are part of a holistically planned business domain strategy.”
“Whereas application programming interfaces, or APIs, are the resulting menu of digital resources and capabilities that are used as the interface to connect applications and integrations.”
“An API might be delivered as part of a Microservices strategy, but is just as likely to employ any number of other architectural styles, or oftentimes, none at all.”
“Microservices architecture and APIs are distinct concepts that solve their own set of problems and have a unique scope, but they achieve similar goals and work from the same principles”, said Jane Flanagan, Lead Project Engineer at Tacuna Systems.
“APIs and microservices are designed to overcome the challenges associated with monolithic deployments.”
“Microservices are more about architectural and design style. You may be able to implement microservices without an API. However, an API makes it easy to build loosely coupled microservices.”
“API Builders enable you to create a dynamic service mesh with API and microservices to unlock the data trapped in your organization and deliver new business value. You can build, assemble and deploy APIs and microservices with a public cloud”
“One of the key design goals when implementing microservices is to create decoupled, independent and small systems that are easy to understand or modify.
“RESTful APIs should belong to one microservice because they are tightly coupled in terms of sharing lots of the same high-level design and architecture.”
“This includes programming language and database access framework.”
“This reduces complexity so you don’t have to maintain a module that uses different technology stacks. Therefore, microservices and APIs solve different problems but work together”

Top Three Benefits Of Splitting An Application Into Microservices

Soheil Salarimanesh, Founder and CTO of ButikRea covered three of the main benefits of separating an application into several microservices below:

1. “Since the modules have been moved to a specific service, the dependency between them has been significantly reduced which makes each service so simple to understand, maintain, improve, extend, and deploy.”
2. Microservice architecture brings the possibility of scalability. With microservice architecture, you can deploy several instances of your product or service which can serve and meet the demands of requests sent to your site/application/web app.
3. Without microservice architecture, if a problem occurs in a part of our application since all the modules are in the same place and dependent on each other, the whole application will crash. However, with microservice architecture, if our checkout service crashes for any kind of reason, another part of our application like the product service can still do their jobs (since as mentioned before, each service is a stand-alone application).