An API Gateway is a single entry point through which all client requests to a set of backend services pass. Instead of letting applications connect directly to dozens of services, we place a single gateway in front of them that routes traffic, authorizes calls, limits load, and aggregates responses. It is a pattern closely tied to microservices architecture, although it can also be useful beyond it.

What an API Gateway Is

An API Gateway works like the reception desk of a large building. Visitors don’t wander the floors looking for the right room — they check in at a single point, where they are verified and directed where they need to go. In an IT system, the building is a set of services, the visitors are client applications (web, mobile, external partners), and the reception desk is exactly the gateway.

Technically, an API Gateway is an intermediary layer between the client and the backend. It receives an HTTP request, makes decisions based on it (where to route it, whether the sender is authorized, whether they haven’t exceeded a limit), and then forwards it to the right service and returns the response. The key point is that the client doesn’t know — and doesn’t need to know — how many services sit behind the gateway or how they are arranged; it sees one consistent API. If you’re just getting started with interfaces, it’s worth first understanding what an API is, because an API Gateway is built on top of that concept.

What Problems an API Gateway Solves

The value of a gateway is best seen through the lens of cross-cutting functions — the ones each service would otherwise have to implement on its own. Four of them are fundamental.

Routing. The gateway routes each request to the right service based on the URL path, headers, or HTTP method. A request to /orders goes to the orders service, and one to /payments — to the payments service. The client addresses a single host, and the gateway untangles it internally. This makes it possible to move, split, and merge services without changes on the client side.

Authorization and authentication. Instead of duplicating identity-verification logic in every service, we check it once — in the gateway. It validates the token (e.g., a JWT), queries the identity provider, and forwards only authorized requests. Backend services can then trust that the traffic reaching them has already been verified.

Rate limiting. The gateway limits the number of requests a single client can make within a given time window. This protects the backend from overload — whether caused by a bug in the client application or a deliberate attack. Limits are set differently for different clients: one way for an internal application, another for a partner using a public API.

Aggregation. A single screen in an application often needs data from several services at once — profile, orders, and recommendations. Without a gateway, the client makes several requests and merges the results itself. The gateway can collect this data in a single client request, query the services in parallel, and return a composite response. Fewer round trips mean a faster application, especially over mobile connections.

API Gateway in Microservices Architecture

In a monolith, all the logic lives in a single application, so the problem of “how does the client reach the right part of the system” practically doesn’t exist. Microservices reverse this situation: a single business domain breaks down into a dozen or several dozen independent services, each with its own API, its own deployment cycle, and often its own team.

If the client had to connect to each service directly, it would need to know their addresses, versions, and authentication rules — and every change on the backend side would force a change in the client application. That’s fragile and doesn’t scale. An API Gateway solves this problem by becoming a stable facade: the internal topology of services can change, while the contract seen by the client stays the same.

The gateway is one of several patterns that bring order to communication in distributed systems. We covered a broader overview — from point-to-point, through ESB and queues, to the API Gateway — in our article on software integration patterns. There, the gateway is one piece of the puzzle; here, we break it down into its component parts.

Usage Patterns: BFF, Aggregation, and Offloading

The API Gateway itself has several established variants of use. The three most important are worth knowing by name, because they recur in nearly every project.

BFF (Backend for Frontend). Instead of one universal gateway for all clients, we create a separate gateway for each type of frontend — one for the web application, another for mobile, a third for partners. Each one assembles responses exactly the way a specific client needs them: the mobile application gets trimmed-down, lightweight data, while the web gets a fuller set. The BFF pattern eliminates the compromises that arise when one API has to satisfy very different consumers.

Gateway aggregation. This is the formal name for the aggregation described earlier: the gateway accepts a single client request, dispatches several requests to services, waits for the responses, and merges them into a single result. This reduces the number of connections the client has to make and shifts orchestration from the client device to a well-networked gateway.

Gateway offloading. This involves moving cross-cutting functions from the services to the gateway — TLS termination, response compression, caching, token verification, or logging. Backend services stop duplicating the same code and can focus on business logic. “Offloading” literally means taking off their shoulders a burden that is better handled in one shared place.

API Gateway vs Load Balancer vs Reverse Proxy

These three elements are sometimes confused, because they all stand “in front of” services and mediate traffic. What sets them apart, however, is the level at which they operate and their scope of responsibility.

A reverse proxy is the most basic of them — it accepts requests on behalf of backend servers and forwards them along, often adding caching, compression, or TLS termination. It doesn’t understand business logic; it’s a neutral intermediary at the HTTP layer.

A load balancer distributes traffic across many identical instances of the same service, ensuring even load and high availability. It usually operates at the transport or network layer and answers the question “which of the ten copies of the service will handle this request,” not “to which service should it be routed.”

An API Gateway operates higher — at the application layer. It understands the content of a request, routes it to different services based on path and headers, authorizes, limits, and aggregates. In practice, these elements coexist: the gateway sits at the front and decides where to route a request, while the load balancer spreads it across the specific instances of a given service. A reverse proxy, in turn, is often the building block on which many gateways are built. These are not competitors, but layers with different jobs.

The tooling market doesn’t need to be built from scratch — there are several mature solutions covering typical needs. Kong is a popular, open gateway based on NGINX, extensible via plugins (authorization, rate limiting, transformations) and proven both in the cloud and on-premise. AWS API Gateway is a managed service in the Amazon ecosystem — it integrates natively with Lambda functions and other AWS services, taking gateway infrastructure maintenance off the team’s hands. NGINX is sometimes used as a lightweight gateway and reverse proxy; it’s not a full-fledged API Gateway “out of the box,” but it handles routing, TLS termination, and basic limiting well, and in its extended version it gains further capabilities.

The choice depends on context: teams deeply embedded in a single cloud often reach for a managed solution, while those that value portability and control go for Kong or NGINX deployed on their own. The gateway itself, however, is just a tool; success is determined by how we configure it and wire it into the rest of the architecture.

API Security

An API Gateway is a natural place to enforce security policies, because it sees all traffic entering the system. Here we terminate TLS, verify tokens, check permissions, limit the number of requests, and reject those that don’t meet the rules before they reach the services. Centralizing these controls is a huge advantage — it’s easier to maintain one consistent set of policies than to police them in each service separately.

The gateway, however, doesn’t relieve services of the duty to look after their own security. The “defense in depth” principle says that a single layer should never be the only line of protection — if someone bypasses the gateway or attacks from the inside, the services must defend themselves. The gateway is the first shield, not the last. We write in more detail about threats and how to protect interfaces in practice in our guide on API security.

When NOT to Use an API Gateway

The gateway solves specific problems, and outside that context it can be a needless cost. For a single monolithic application serving one type of client, an API Gateway adds a layer that increases latency, complicates deployments, and requires maintenance — without giving much in return, because there’s nothing to route between and nothing to aggregate.

The gateway also introduces the risk of a single point of failure. Since all traffic passes through it, its outage means the entire system is unavailable. So you have to plan for redundancy and monitoring, which is an additional operational effort. Finally, a poorly designed gateway easily becomes a “new monolith” — a bag into which teams stuff business logic until it stops being a thin routing layer and starts being a development bottleneck. The break-even point appears only when we have many services and many different clients; before that point, a simpler approach usually wins.

Best Practices

If the decision to use a gateway has been made, a few principles separate a successful implementation from one that will become a problem in a year.

  • Keep the gateway thin. Routing, authorization, limiting, aggregation — yes. Business logic — no. That belongs to the services. When the gateway starts to “know” about domain rules, it turns into yet another monolith.
  • Plan for high availability. As a single entry point, the gateway must be redundant and monitored. Its outage must not be the outage of the entire system.
  • Version your API. Define contracts formally (e.g., OpenAPI) and version them so that changes don’t break existing consumers.
  • Observability from the start. The gateway sees all traffic — it’s the ideal place for consistent logging, metrics, and alerts. Wire them in from day one, not after the first incident.
  • Mind the latency. Every hop has a cost. Cache where it’s safe, query services in parallel when aggregating, and measure the time the gateway adds to a request.
  • Don’t make the gateway the only shield. Enforce security at the gateway, but don’t trust it unconditionally — backend services must also validate input and authorize access.

In practice, an API Gateway is one element of a larger integration puzzle. We write about how to connect systems at the enterprise level in our article on IT systems and API integration, and you’ll find a definition of the pattern itself in the glossary (API Gateway).

How ARDURA Consulting Supports API Architecture and Integration

At ARDURA Consulting, we treat the API Gateway as an architectural decision, not a default add-on to every project. We start by asking how many services, how many clients, and which cross-cutting functions actually exist in the system — and only on that basis do we recommend a gateway or deliberately forgo one. When we do implement it, we make sure it stays thin, available, and observable, and that it enforces security without becoming the only line of defense.

We deliver projects in two models. As part of ARDURA Consulting’s software development services, we take full responsibility for designing and implementing the API layer — from contracts and routing, through authorization and rate limiting, to monitoring. In the staff augmentation model, we strengthen the client’s team with senior specialists who know these patterns from practice and onboard into the project in about 2 weeks. Behind this stand more than 500 senior specialists and 211+ completed projects, and specialist retention at 99% means continuity of competence throughout the entire collaboration.

If you’re designing a microservices architecture, grappling with a tangle of direct connections, or wondering whether an API Gateway will solve your problem or just add a layer — let’s talk about your project. We’ll help you choose a solution that will work not just today, but also after another ten services.