An API gateway routes requests, but its broader architectural role is to provide a shared place to apply selected policies at the API boundary. When configured, it can handle concerns such as TLS termination, authentication, client throttling, and request telemetry for multiple services. It is not literally every cross-cutting concern, and it does not replace the authorization, validation, or business rules each service must enforce.
What an API gateway does
An API gateway is a reverse proxy and shared entry point between API clients and application services. Microsoft Learn describes it as “a centralized entry point for managing interactions between clients and application services.” It routes requests to back-end services, but teams can also configure it to enforce policies consistently before traffic reaches those services.
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That policy boundary is the difference between thinking of a gateway only as a router and using it as an API gateway pattern. A router selects where traffic goes. A gateway can make that decision and apply API-facing controls along the request path.
Which concerns can a gateway centralize?
The exact feature set depends on the product, deployment, and enabled configuration. Possible gateway functions include:
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- Transport security: terminate SSL/TLS connections or, where supported and configured, handle mutual TLS.
- Client access policy: authenticate callers, apply IP allow or block lists, and enforce client rate limits or throttling.
- Operations: collect request logs and monitoring data, and in some implementations provide response caching.
- Request and response handling: apply a web application firewall (WAF), compress responses with GZIP, or serve static content.
- API composition: aggregate calls to multiple services so a client can make one request for a combined response.
These are capabilities to verify, not a checklist every gateway automatically provides. Microsoft notes that support for features such as authentication, rate limiting, and SSL termination varies across gateway options. Apache APISIX describes its request flow as matching Routes, selecting Upstreams, and running explicitly configured plugins. In other words, the policy is present only when the implementation supports it and the team configures it.
Why centralize policies—and what must stay in services
When several public-facing services need the same client-facing controls, enforcing selected policies at a shared boundary can reduce duplicated handling. It can also let clients use a stable API entry point while teams change how the underlying services are divided or deployed.
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Centralization is not a substitute for service-level safeguards. A gateway may authenticate a caller, but each service still needs to decide whether that caller may access a particular resource. Services must also validate input, check business state, and enforce workflow rules. APISIX explicitly cautions that gateway capabilities do not automatically replace service authorization, data validation, workflow-state checks, or business logic.
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Nor does a gateway make an application invulnerable. Rate limiting by itself is not complete DDoS protection, and filtering requests at the edge cannot protect an upstream application from every vulnerability.
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API gateway vs. router, reverse proxy, service mesh, and Kubernetes Gateway API
Router and reverse proxy
An API gateway is itself a reverse proxy; routing remains one of its core jobs. The architectural distinction is the additional API-facing policy boundary and lifecycle that a deployment places at that entry point. A basic router can direct traffic without providing the same set of configured API consumer controls.
API gateway and service mesh
“What is the difference between an API gateway and a service mesh?” is a common question, but the answer is not simply that gateways handle north-south traffic and meshes handle east-west traffic. The CNCF comparison calls that shorthand inaccurate: clients can be inside or outside an organization, and the distinction is better understood through the responsibilities each pattern emphasizes.
Gateways commonly focus on API consumers and API products—for example, consumer authentication and authorization, rate limits, developer onboarding, monetization, and client-application governance. Meshes commonly focus on service connectivity and service-to-service behavior, potentially across Layer 4 and Layer 7. The patterns overlap, and an organization may use both. Decide based on the policies and traffic relationships you need to govern, not direction alone.
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Kubernetes Gateway API is a Kubernetes resource interface for service networking and routing, not another name for a gateway product. Its role-oriented resources—such as GatewayClass, Gateway, and route resources—describe the interface and how an implementation relates to it. Gateway API supports ingress and has mesh use cases; some API gateway products can be programmed through it.
Operational trade-offs to plan for
Because requests pass through the gateway, it becomes an operational boundary on the request path. Design for its availability and capacity, account for the latency it may add, assign clear ownership for policy and configuration, and use safe rollout practices. These are consequences of putting a shared component in the path, not evidence of a fixed performance penalty.
Throttling also needs a defined scope and failure behavior. For example, AWS documents API Gateway throttles as best-effort targets implemented with a token bucket. Clients may receive HTTP 429 responses after exceeding configured rate or burst targets, so do not treat a configured limit as a guaranteed exact ceiling.
A gateway does not necessarily replace a load balancer. Azure API Management, for example, does not perform load balancing and may be paired with a load balancer or reverse proxy. Nor must one gateway serve every audience or environment: deployments may use public, regional, environment-specific, or audience-specific gateways.
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Compare candidate gateways against the policies and operating model you actually need. Microsoft’s guidance distinguishes options such as reverse proxies (including NGINX and HAProxy), service-mesh ingress gateways, Azure Application Gateway, Azure Front Door, and Azure API Management; their feature profiles differ. Check support for required features rather than assuming a product label guarantees them, and consider built-in platform offerings when they meet your security and control requirements.
- Policy requirements: confirm the exact authentication, TLS, rate-limit, IP policy, logging, caching, WAF, or other capabilities you need, including where each is enforced.
- API product needs: decide whether you need consumer onboarding, client-application governance, or other API lifecycle controls in addition to routing.
- Deployment and control: assess where the gateway runs, who owns its configuration, and how it fits the platform and operational responsibilities you already have.
- Mesh and platform integration: establish whether the gateway should work alongside a service mesh or be managed through an interface such as Kubernetes Gateway API.
- Failure and rollout behavior: understand how the chosen implementation handles unavailable upstreams, policy changes, scaling, and configuration mistakes.
Spring Cloud Gateway is one example in the Spring ecosystem. Its documentation describes routing alongside security, monitoring and metrics, and resiliency features; its full-featured server variant can run standalone or be embedded. That makes it a candidate to evaluate in a Spring-oriented environment, not a universal fit.
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