Microservices vs API

The terms API and microservices are often thrown around pretty loosely. What do these terms actually mean? How do they relate to one another? In this piece, we’ll tackle these questions, as well as answer some common misconceptions in the space.

What is an API?

Before we discuss microservices, we should first define what an API actually is at its most basic level. An API, or Application Programming Interface, is a set of rules and protocols governing the interaction between software applications. In essence, it acts as a sort of Rosetta Stone, setting the core language by which applications across environments can communicate. APIs exist locally, such as those within your computer which govern graphics processing, memory allocation, file storage, etc., but also exist on the macro level, connecting web APIs to resource servers, machines to machines, and so forth.

In the context of web APIs, these APIs typically bridge a connection between clients and servers. They take an instruction – say, “get the current status of a user record” – and convert it into a machine-usable command – such as “curl -X GET “https://api.io/v1/users/user10” -H “accept: application/json””.

Notably, how these APIs work can take a few different forms, and you will often hear a set of acronyms bandied about in the world of web APIs. REST, or Representational State Transfer, is a [way of connecting clients and servers](https://www.codecademy.com/article/what-is-rest) without requiring that either know anything about the other. SOAP, or Simple Object Access Protocol, is a more tightly coupled paradigm that is typically used for handling secure records requiring a high level of coupling and synchronicity. Other solutions such as GraphQL utilize novel methods of organizing and retrieving data, making it easier for APIs to do more complex functions such as replying to requests with custom data formats and structures.

Benefits of an API Paradigm

APIs are the powerhouse of the modern internet and web – they power the complex interactions between clients, servers, and services, unlocking amazing functionality by providing a common language of communication.

Beyond this connective benefit, APIs offer some attributes that make it more powerful than localized apps or mainframe operations:

• Interoperability. APIs seldom care about what is connecting, and mostly care about how they’re connecting. For this reason, APIs provide an infrastructural interoperability that allows for discrete systems and functions which would otherwise be incompatible to connect and cooperate.
• Efficiency. APIs allow for the same server functions and resources to be used across multiple development situations, reducing development time by creating portable and reusable functions.
• Scalability. By decoupling from centralization applications, modular development is made possible. Existing functions and resources can be tied to new API endpoints or actions, thereby allowing new development without having to change the entirety of the stack underpinning it all.
• Cost control. APIs operate on a per-request basis, and as such, limited resources can be controlled granularly by throttling or reducing access.

Pros and Cons of APIs

The Monolithic Paradigm

In the early days of API development, everything was based on centralization. A user could call up a system to perform an action using its resources, often a mainframe or central server, and the results would be pushed to the user. 

This often created tight coupling between the request and the resources underpinning it, resulting in a development style known as “The Monolith”. In the monolith, there was a single, unified software architecture where all components are interconnected and interdependent. The interface and its systems were bundled together, and any change that happened to a component meant the entire system had to be updated.

This “one stop shop” approach typically resulted in a single codebase, shared resources, and centralized management.

Pros and Cons of the Monolith

What are Microservices?

As the monolith began to show itself as problematic, a new approach was needed to connect services without the baggage of a centralized solution. Microservices were developed as an architectural style to solve many of these problems. In essence, microservices is a style in which an application is composed of small, independent services that communicate over a network. Each piece of system is broken into discrete units, and are bundled with the resources and systems needed to function in concert with others.

Imagine an API which contains student names, their grades, their enrollment data, and so forth. In the monolith, all of this would exist as a single server somewhere with a single endpoint to interact with. In a microservices paradigm, there might be a StudentData service, a ClassroomData service, a Grades database, an EnrollmentManager service, etc. If a new service needs to be developed – say we’re adding a Gym that is accessible only to enrolled students – that service, GymAccess, can be added independently from the rest.

This approach is an answer to the issues of the monolith, breaking individual components, functions, and processes into discrete units.

Benefits of the Microservice Model

Scalability. The microservices model makes it easier to scale individual services based on demand, allowing for new resources to be added as needed without updating the core codebase.

• Extensible. New development has reduced cost both temporally and monetarily, as new components are easier to create than new monolithic branches.
• Flexibility. Microservices enable the use of different technologies for different services, eliminating the “one size fits all” approach of the monolith.
• Resilience. Fault isolation ensures that a failure in one service doesn’t affect the entire application, increasing both security and service uptime.

Pros and Cons of Microservices

Differences in Documentation

It bears mention that microservices require some changes in how they’re documented compared to typical software solutions. Microservices documentation requires highly detailed information about each service’s internal architecture, dependencies, deployment processes, and configurations, as the entire network should have context around its communication. It also requires substantial documentation around security, transport, authentication, and authorization within the system, as modular components mean a heightened focus on transit of data between constituent parts.

API documentation tends to focus on endpoints, request/response formats, authentication methods, and usage examples. General API documentation is largely more focused on infrastructure, and less so on design documentation. In the case of microservices, this design documentation is very necessary, as it exposes the design paradigm which the API was created under, which is vital for understanding the way the system works.

Let’s look at some differences in documentation approaches between general APIs and microservices.

Scope & Detail

Microservices documentation dives into the nitty-gritty of how services are structured and configured, while API documentation focuses on how external users interact with the system. One is about the “behind-the-scenes blueprint,” and the other is the “user-facing manual.”

Inter-Service Communication

Microservices documentation explains how services talk to each other within the system, using protocols, events, and discovery tools, while API documentation shows how outsiders can interact with the system via endpoints and integrations. Think of it as the “internal chatter vs. external conversations.”

Operational Aspects

Microservices documentation covers everything about keeping services running smoothly—deployment, monitoring, scaling, and resilience strategies. API documentation, on the other hand, helps developers use the API efficiently with practical usage guidelines. It’s the difference between “system maintenance” and “developer onboarding.”

Maintenance and Updates

Microservices documentation outlines how services evolve over time, with clear strategies for versioning and upgrading, while API documentation ensures users know what’s changing and how to adapt. One handles “internal upgrades,” the other manages “external compatibility.”

Security Considerations

Microservices documentation secures the system internally with protocols, access control, and encryption. API documentation ensures external users interact securely through authentication, authorization, and communication safeguards. It’s “fortress security” for the inside and “guarded gates” for the outside.

Use Cases and Applications for Microservices and APIs

APIs and microservices often have the same use cases due to how they relate to one another, but there are specific use cases that are more appropriate for standard APIs than microservices (and vice versa).

Let’s take a look at a few of them now.

Microservices Use Cases

Financial services

When there is a need to separate services between different products, branches, and partners, microservices shine. In the financial sector, separate services for user accounts, transactions, fraud detection, analytics, and more are relatively commonplace.

Logistics and supply chain

Modular services for inventory management, shipping, order tracking, and customer notifications are relatively common in the logistics space.

Social media platforms

Social media platforms often contain many different services, often services that were designed independently and then acquired. In this case, microservices can play a huge role in connecting these disparate services and providing a central backbone for communication. 

Standard API Use Cases

Cloud services

As cloud services are essentially local services moved to remote servers, they often benefit from having standard APIs serving infrastructural purposes. 

IoT devices

As IoT devices often have low memory and processing allowances, their internal systems typically run as a lean single API – although they can be part of a larger microservice collection, this microservice exists outside of the core device.

Differences in Deployment Strategies

Due to their different methods of connecting systems and resources, standard APIs and microservices often see different deployment strategies.

Monitoring and Management

Monitoring and management can also differ significantly between core APIs and microservice implementations.

Scalability and Performance

Scalability and performance considerations are very different when comparing singular APIs versus microservices.

Common Misconceptions about Microservices and APIs

Microservices and APIs – Are They the Same Thing?

Microservices and APIs are not the same thing, but they are intimately related. This is a bit of a “square” and “rectangle” situation – all microservices are APIs, but not all APIs are microservices.

Microservices are an architectural style; APIs are a method of communication.

Microservices are APIs in segmentation – the opposite of a microservice isn’t an API, it’s a monolith.

Do Microservices Require APIs for Communication?

Generally, microservices require APIs to communicate. The very nature of a microservice means that its communication framework is probably separate from its codebase. The specific language, framework, etc. chosen by the developer is often implemented in the transit layer through a gateway, shim, or other frontend. In this way, you could say that an API is required for communication as the API converts the internal functions and logic of the microservice to the external – but this is a bit like asking “do highways need roads”.

Are APIs Only Used by Microservices?

APIs are best thought of like infrastructure. APIs are the highways and roads that connect our cities (services) together. The paradigms that work on top of these connections don’t define the underlying structure.

APIs can be used by a wide variety of systems and services. While microservices use APIs by their core nature, APIs can also be used in non-networked computers to draw graphics, or in medical devices to connect data storage with measurement devices. APIs are used anywhere technology exists.

Is The Performance Improvement in Microservices Guaranteed?

The performance improvement promised by microservices depends a lot on how it’s implemented. It’s not necessarily true that simply developing a microservice will generate huge gains in performance – performance is a multifaceted question, and this can shift depending on specific needs, implementation, environment controls, etc.

In essence, it’s possible to do microservices “incorrectly” or “poorly”, and it’s also possible to make a perfect microservice that fails due to network limitations.

Conclusion

In conclusion, microservices and APIs are intimately related – whereas APIs are infrastructural solutions, microservices are a paradigm which focuses on making lots of little APIs instead of a single monolithic codebase. It’s possible to use an API without using a microservice, but you must use an API to have a microservice.

Microservices provide more extensibility and scalability, but this is traded off with additional complexity as each component is individually crafted as part of a cohesive network. APIs in their raw form are simpler, but far less efficient in terms of scalability and extensibility, and novel development is often quite expensive, as you must update the entire codebase instead of just a singular piece or part.