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APIs and Web Services are often used interchangeably, yet the distinction between them is more important than it seems. So where does this difference really begin, and how did growing integration complexity give rise to the need for API Gateways? This article explores the role of API Gateways and the core capabilities they bring to modern architectures.
A Perspective on APIs, Web Services, and API Management
For many years, two fundamental concepts have consistently appeared alongside the evolution of flexibility, integration capabilities, and distributed architectures in the software world: APIs and API Management. In recent years, these concepts have moved beyond purely technical teams and become part of the agenda for product and business stakeholders as well. The main reason for this shift is that systems are no longer isolated and closed structures; instead, they have evolved into living ecosystems shaped by numerous internal and external integrations.
In this article, I will explore what an API is, where the distinction between APIs and Web Services truly begins, and why components such as API Gateways have become essential today. Rather than focusing solely on theoretical definitions, I will approach these questions through architectural and operational realities.
An API (Application Programming Interface), in its simplest form, is an interface that defines how two software components communicate with each other. It specifies which capabilities an application exposes to another application and under what rules.
Although today the term API is often associated with services accessed over the internet, this represents only a small part of the concept. APIs have existed long before the web. Communication between two applications running on the same machine—or even between modules within a single application—also happens through APIs. This interaction does not always require HTTP, REST, or even a network connection.
Functions provided by operating systems, methods exposed by software libraries, or custom protocols that transfer raw data over TCP are all examples of APIs. Therefore, limiting the concept of an API to “web services” alone means overlooking its architectural depth.
A Web Service is a narrower and more specific subset of the API concept. It refers to structures that enable two systems to communicate over a network, most commonly using HTTP or HTTPS.
A Web Service listens for incoming requests on a specific endpoint and produces a response accordingly. That response may consist of structured data such as JSON or XML, but it can also be HTML, images, or other types of binary content. The key distinguishing factor here is that Web Services are inherently network-dependent.
In other words, when we talk about a Web Service, communication over a network is always involved.
Although these two concepts are often used interchangeably in daily conversation, they do not mean the same thing from a technical perspective. Every Web Service is an API because it exposes an interface to the outside world. However, not every API is a Web Service, since APIs do not require web protocols or a network connection to function.
Web Services are constrained by specific communication models such as SOAP, REST, or XML-RPC, whereas APIs have no such obligation. This distinction becomes particularly critical when designing architectures or defining integration strategies.
APIs have been part of our systems for a long time, but in the past, most of them were used between a limited number of systems located within the same data center. Integration scenarios were relatively few, and management was comparatively straightforward.
With the widespread adoption of cloud technologies, this picture changed fundamentally. Services became geographically distributed, the number of systems increased, and both internal and external integrations diversified significantly. This diversification led to the emergence of an uncontrolled and rapidly growing API ecosystem.
Backend services that were initially meant to contain only business logic gradually started to take on additional responsibilities in order to meet new integration requirements, such as:
As a result, business logic and integration-related code became tightly coupled, producing fragile systems that were difficult to change and maintain. The need to remove this burden from backend services and manage common integration concerns from a central point gave rise to the concept of the API Gateway.
An API Gateway is a centralized layer positioned between clients and backend services. Its primary purpose is to separate common integration concerns from backend services and manage them consistently from a single point.
With this approach, backend services become simpler, more autonomous components that focus solely on their core business responsibilities.
The value of a modern API Gateway does not come solely from routing traffic, but from centralizing the integration-related responsibilities that accumulate around services over time. These capabilities elevate the Gateway from a simple proxy to a strategic architectural component.
A modern API Gateway typically provides value across six main areas.
Authentication and authorization are common challenges in almost every integration scenario. Determining who can call a service and at what level of access is often independent of the service’s business logic. Historically, however, these controls were embedded directly into backend code, causing services to become increasingly complex as integration scenarios multiplied.
With an API Gateway approach, authentication and authorization can be fully managed at the gateway layer. Supported mechanisms typically include:
For example, a service protected by LDAP at the backend can be exposed to external consumers via OAuth. These two different security models are bridged at the Gateway level, completely isolating the backend service from this complexity. This approach not only enhances security but also significantly improves service reusability.
In real-world integrations, it is unrealistic to expect all systems to communicate using the same data format. A SOAP-based service that has been used internally for years may need to be consumed by a newly developed mobile or web application over REST.
API Gateways prevent backend complexity by handling transformations such as SOAP-to-REST or XML-to-JSON at the gateway level. In addition, the Gateway can perform:
As a result, malformed, incomplete, or unexpected requests are blocked before they reach backend systems. This approach protects backend resources and directly improves overall system stability.
It is impossible to manage a service effectively without understanding how it is being used. API Gateways make all traffic passing through them centrally observable.
Through the Gateway, it is possible to collect:
These data can be stored within the Gateway itself or forwarded to external systems such as ELK, SIEM, or similar platforms. This visibility allows service owners to clearly see who is using their services, how often they are called, and under which scenarios issues occur.
Traffic patterns for internet-facing services are rarely predictable. Unexpected spikes or malicious requests can easily cause system-wide outages.
API Gateways use mechanisms such as:
to ensure that critical services remain available even under heavy load. Instead of a total system failure, this approach enables controlled degradation.
As the number of services grows, the question “Which service does what?” quickly becomes a serious problem. The centralized API Catalog provided by API Gateways allows services to be listed in a single place, with up-to-date documentation readily accessible.
This structure:
and contributes to the development of a shared API culture across the organization.
API Gateways serve as the first line of defense for services exposed to the outside world. Attacks covered by the OWASP Top 10—such as SQL Injection, XSS, and DDoS—can be blocked at the Gateway level before they ever reach backend systems.
Enterprise-grade and licensed solutions provide regular security updates, allowing rapid adaptation to newly discovered attack vectors. This significantly reduces operational risk, especially for organizations with a high number of external integrations.
Using an API Gateway provides organizations with not only technical but also operational and strategic advantages. Reducing integration complexity, centralizing security, and simplifying backend services are among the most important of these benefits.
In short, an API Gateway is not just a technical tool. When designed correctly, it becomes a critical architectural component that makes an organization’s API ecosystem sustainable, manageable, and scalable.
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