What Is an API Gateway? How It Works & Why You Need One

API gateway architecture and key features: an API gateway is a single entry point that sits between API consumers and backend services. Its architecture pairs a data plane (a reverse proxy, such as Envoy, that routes, transforms, and load-balances requests) with a control plane where routes and policies are configured. Its key features are request routing, authentication and authorization, rate limiting, protocol transformation, and observability, so every API call is secured and measured in one place.

What is an API Gateway?

An API gateway acts as reverse proxy, a tool situated in front of one or more APIs, which can serve as a single point of contact for external API consumers, as well as internal APIs and microservices. The gateway enforces security policies to protect against threats, and efficiently routes traffic between API producers and consumers.

An API gateway works by receiving API requests from a client, aggregating multiple requests, and routing them to the required services. When responses are received, the API gateway similarly aggregates them and routes them back to the user.

Read more about API gateways in a cloud native world

Why use an API Gateway?

Modern cloud native applications based on a microservices architecture frequently utilize API gateways. These applications usually consist of autonomous, independent, single-function components known as microservices. These components are loosely coupled and typically connected to their own databases. You can deploy, maintain and test each microservice independently.

Handling requests

Microservices enable you to easily develop, deploy, and maintain different application functions, but they also make it difficult for external users to quickly and securely access the application. An API gateway helps solve this issue. Instead of asking customers to request access to each microservice separately, the gateway provides a single point of entry for all requests.

Once a request for information comes into a microservices-based application, the API gateway retrieves and returns the data, streamlining this process. It sends them to the relevant service, collects results, and sends them back to the customer. The gateway handles access control and also allows reliable and fast delivery in large, complex applications.

Routing traffic

An API gateway provides a management interface for many important aspects of the application. It serves as the main proxy that connects customers to services, supporting security and administration functions such as metric collection, authentication, response transformation, and input validation.

Each microservice runs in an independent environment, allowing you to add, upgrade, move and change them without affecting the overall application. API gateways enable you to easily route traffic and scale up microservices applications.

Learn more in our detailed guide to API gateways and microservices

How do API Gateways work?

Using an API gateway decouples the client interface from the backend implementation of a microservices architecture. API consumers only communicate with the API gateway, which provides an easier and more consistent experience than integrating with each backend API provider.

When an API consumer sends a request to the API Gateway, the following process occurs:

• Request flow—the request is approved, validated, and translated against the backend endpoint. At this stage, API providers can request specific HTTP headers, query parameters and query strings, or API keys to identify the caller, block fraudulent requests, or impose limits or quotas.
• Routing requests—the API gateway is able to map between user requests and the backend services that can fulfill each request. Request routing to one or more relevant services. Multiple incoming requests for the same API are packaged into a single request to improve performance.
• Response flow—when APIs respond, the API gateway collects responses from multiple services and sends them back to the client. In the same way as requests, multiple responses may be aggregated into a single response. This response typically includes an HTTP status code confirming that the request was successful.

API Gateway Architecture

API gateways are a key component of modern microservices architectures, serving as a centralized entry point for managing API requests. They facilitate seamless integration between client applications and backend services by standardizing service networking. The architecture of an API gateway typically includes components for traffic management, request routing, user authentication, and protocol translation. By acting as a reverse proxy, the API gateway efficiently routes incoming requests to the appropriate backend services, ensuring optimal resource utilization and enforcing security policies. This centralized platform also supports caching responses, dynamic load balancing, and concurrent API calls, enhancing the overall API performance and reliability. Additionally, API gateways ensure that requests are directed to the appropriate services, optimizing the flow of data and resources.

‍Learn more about moving to a modern API gateway

The Evolution of API Gateways

Several factors are reshaping how users evaluate API Gateways:

• How well does it scale to handle a larger volume of API traffic?
• How well does it perform at a larger scale?
• How well does it consistently deliver low-latency response times?
• Does it natively work in public cloud or any Kubernetes environments?
• Does it leverage the latest innovations in proxy technologies (e.g. Envoy Proxy)?
• Does it leverage the latest open source innovations around proxy technologies (e.g. WebAssembly or GraphQL)?

As each of these issues become more impactful to how an API Gateway can enable your microservice applications, the more companies are beginning to choose Solo.io kgateway. Based on Envoy Proxy, kgateway enables greater scalability and latency than legacy API Gateways based on NGINX, HAProxy or Java-wrappers on proxy technology.

In addition, kgateway is both public cloud native and Kubernetes native, so integrating with DevOps environments is seamless. And kgateway enables users to easily add new innovations such as Web Assembly or GraphQL to their API Gateway environment to handle next-generation application needs.

5 key capabilities of API gateways

1. API Security

Access control is a major driver for the adoption of API gateway technology. An API gateway must provide an authentication layer so that only authenticated users can access a a backend service or API. It should also be able to integrate with existing authentication providers, such as API keys, JSON web tokens (JWT), lightweight directory access protocol (LDAP), OAuth, OpenID Connect (OIDC), and custom services.

Once an account is authenticated, the API gateway authorizes the targets it is allowed to access. An API gateway should also support authorization—this means it should be able to abstract the structure of backend APIs and control user access to specific functions, data, or operations. An API gateway must be able to leverage existing authorization mechanisms such as role-based access control (RBAC).

Learn more in our detailed guide to API gateway security

2. Rate-Limiting

An API gateway reduces load on backend APIs and helps prevent abuse. Rate limiting limits access to the API, only allowing a certain number of requests per period, user, or group of users. Rate limiting makes it possible to expose APIs safely to third-party consumers, creating new revenue opportunities.

3. API Monitoring and Logging

An API gateway should provide basic monitoring for all APIs and be able to track requests, response times, and service level agreements (SLAs). The API gateway should also provide unified logging for all APIs to improve developer productivity. Logs should include a request ID, which makes it possible to correlate request headers with API activities, to enable end-to-end debugging.

4. API Transformation

An API gateway must provide the ability to transform request and response payloads. Payload transformation can support organizations moving from traditional SOAP-based architectures to modern REST-based API architectures, and can help accelerate time to market for app delivery.

5. API Scalability

API gateways typically do not perform autoscaling out of the box, but they should integrate with a service that provides this functionality. API gateway must support scalability, high availability, load balancing, and shared state without compromising performance.

Benefits and challenges of API gateways

API gateways standardize and centralize the delivery of services via APIs and help organize and secure API integrations. The main benefits of an API gateway are:

• Simplified service delivery—concurrent API calls can be combined to request services, reducing the traffic volume and streamlining API processes to improve user experience.
• Flexibility—easily configure the gateway to encapsulate the application's internal structure and invoke backend services.
• Legacy app integration—extend the functionality of legacy apps instead of refactoring or adopting new apps for seamless integration.
• Observability—monitor API activity with logs to pinpoint issues during failures.

However, API gateways also have challenges as the gatekeepers between API providers and consumers:

• Resilience and reliability—malfunctions in the API gateway can cause associated services to fail, unless they are configured for high-availability. Organizations should avoid adding redundant features that impact performance.
• Security—API gateways are trusted secure access points within the corporate network so that any compromise can affect the whole organization. It is important to separate internal and outward-facing APIs.

Complex dependencies—gateways require updates for each change to an API. API design rules and standards can mitigate this complexity.

API Gateway vs. API Management

API management solutions enable you to manage the entire API lifecycle from a single entry point. You can use these solutions to manage how you publish and share APIs with developers and partners, and control client requests for who can access each API according to specific user roles and permissions.

They also provide monitoring functionality to track usage statistics for each published API. These insights can answer important questions, such as which APIs are most popular among external clients, how clients interact with APIs after they are published, the geo-distribution of requests, and how many API per second each endpoint receives.

API gateways might be components within an overall API management solution, or they can be used as a standalone solution depending on your desired API composition. An API gateway is only a proxy server situated in front of existing infrastructure, while an API management solution encompasses the entire API lifecycle.

Organizations typically use API gateways and API management platforms together to:

• Enhance the backend architecture and gain more control over a multi-API system.
• Improve observability of API-based applications.
• Improve end-user experiences by ensuring secure, reliable, and efficient delivery of API services across distributed environments.

API Gateway vs. Service Mesh

A service mesh is an infrastructure layer that focuses on managing internal communication, handling communication within a microservices-based application. It works by abstracting the network layer from the application and handles all traffic controls to ensure security and policy enforcement within the network.

Kubernetes and virtual machine (VM) workloads leverage a service mesh to handle communication between services and traffic routing from external clients into the application. A service mesh can manage both north-south traffic (among services within a data center) and east-west traffic (services communicating across data centers) for better resource utilization.

An API gateway focuses on managing incoming request traffic from external users. In smaller implementations, it can be used to manage inter-service traffic as well. API gateways can support simple use-cases, including:

• Authentication and authorization
• Protocol compatibility
• Layer 7 level routing
• Rate limiting

Once a microservices architecture scales up, API gateways alone are not enough, because they cannot support use cases like end-to-end encryption of network communication and advanced deployment strategies. Larger microservices deployments typically use a service mesh in combination with an API gateway to achieve efficient global traffic management and secure communication.

Learn more in our detailed guide to service mesh vs. API gateway

API gateway vs. load balancer

API gateways and load balancers can handle network traffic but work differently. Since an enterprise network typically sees high traffic volumes, an application running on a single server might lack sufficient compute or network power to handle all received traffic requests. A load balancer routes incoming requests for network traffic between two or more servers.

An API gateway manages network traffic differently. Modern software increasingly relies on APIs to integrate disparate application components and enable them to communicate. An API gateway receives API requests from a client and determines the destination services or applications required to handle these calls. It also manages all protocol translation between different software components.

Enterprises can use API gateways and load balancers together. For example, you can employ an API gateway to connect microservices and load balancers, and define how traffic should be distributed between multiple instances of a microservice while enforcing security policies related to such activities.

How Solo.io can help with API management

Solo Enterprise for kgateway is a cloud-native API connectivity solution that unifies API management across external, internal, and third-party APIs, providing robust API traffic management capabilities.

Built on the market-leading Envoy Proxy, Solo Enterprise for kgateway brings API management into the cloud-native era, offering self-service to API development teams backed by automated guardrails that platform teams require to secure, scale, and monitor APIs in production.

Analytics and monetization

Advanced API usage metrics and analytics in the application programming interface allow you to monitor API health and performance, measure business impact of API products, and monetize API consumption.

Developer portal

Modernize your public API presence with a React-based developer portal that is ready to deploy out of the box. Support internal teams with comprehensive Backstage integration for internal developer portals.

Multi-cluster

A federated control plane allows centralized deployment, management, and monitoring across on-premise and cloud environments. Delegated routing, failover, and discovery provide best-in-class flexibility and scale for distributed deployment architectures.

Learn more about Solo Enterprise for kgateway and the additional features it provides platform teams.

API Gateway Architecture and Key Features

API gateway architecture and key features play a central role in shaping how modern applications interact, scale, and remain secure. This section explains what constitutes a robust API gateway architecture and why specific features matter for organizations building cloud-native or microservices-based solutions.

What is API Gateway Architecture?

API gateway architecture refers to the arrangement and interaction of gateway components that sit between API consumers (such as applications or clients) and backend services or microservices. The gateway acts as a centralized entry point, routing requests intelligently, enforcing security policies, managing traffic, transforming protocols, and often providing monitoring capabilities. A well-designed architecture ensures high availability, scalability, and the ability to iterate services independently while maintaining strong governance and security.

Key Features of API Gateways

• Request Routing & Load Balancing: Intelligently directs traffic to appropriate microservices, ensuring availability and scalability.
• Authentication & Authorization: Enforces access control policies, supports OAuth, JWT, API keys, and integrates with identity providers.
• Rate Limiting & Throttling: Controls API usage to prevent abuse and ensure fair allocation of resources.
• API Security: Protects against common threats such as DDoS, injection attacks, and provides TLS termination.
• Protocol Transformation: Converts between protocols (REST, gRPC, SOAP, WebSockets) for compatibility between clients and services.
• Monitoring & Analytics: Tracks API usage, performance, error rates, and integrates with observability tools for actionable insights.
• Traffic Management: Implements A/B testing, canary releases, retries, circuit breaking, and service discovery integration.

Comparing API Gateway Features

Different API gateways may emphasize unique capabilities based on deployment models (cloud-native, hybrid, on-prem), scalability needs, and integration options. For instance, open-source solutions often prioritize extensibility, while managed gateways focus on ease of use and deep integration with platform services. Evaluating gateway options involves considering maturity, community support, integration possibilities, and the depth of features you require. For more details, see Solo.io's approach to modern API gateways at kgateway.

Frequently Asked Questions

What is the difference between an API gateway and a load balancer?

While both tools distribute requests, an API gateway provides rich API-specific features—like authentication, protocol transformation, and response aggregation—whereas a load balancer primarily distributes traffic based on health and capacity, lacking deep API management functionalities.

Why are key features like authentication and monitoring critical?

Authentication ensures only authorized users access services, limiting risk of data breaches. Monitoring enables visibility into traffic patterns, usage, and application health, making it essential for troubleshooting and scaling APIs effectively.

How does API gateway architecture support microservices?

By aggregating requests, centralizing access control, and abstracting individual service details, API gateway architecture simplifies interactions for clients and reduces the operational complexity of managing distributed microservices environments.

What is API gateway architecture?

API gateway architecture is how a gateway is placed and built between clients and backend services. Clients send every request to the gateway, which authenticates the caller, applies policies such as rate limits, routes the request to the right service, and returns the response. Modern cloud-native gateways separate a data plane (the proxy that handles traffic) from a control plane (where routes and policies are defined), often configured declaratively through the Kubernetes Gateway API.

What are the key features of an API gateway?

The core features are request routing and load balancing; authentication and authorization with API keys, OAuth, or JWT; rate limiting and quotas; request and response transformation, including protocol translation such as REST to gRPC; caching; and observability through metrics, logs, and traces. Many gateways also add a web application firewall, developer portal integration, and traffic controls such as retries, timeouts, and canary releases.

API gateway vs. service mesh: when do I need both?

An API gateway manages north-south traffic: requests entering your platform from external clients. A service mesh manages east-west traffic between services inside the platform, adding mTLS, retries, and service-to-service observability. Teams running many microservices on Kubernetes usually need both: the gateway as the controlled front door, and the mesh to secure and observe what happens behind it.

How do kgateway and agentgateway fit into API gateway architecture?

kgateway is an open source, Envoy-based API gateway built on the Kubernetes Gateway API that handles ingress routing, security, and traffic policy for microservices. agentgateway applies the same gateway pattern to AI traffic, connecting applications and agents to LLMs, MCP tools, and other agents with authentication, rate limiting, and observability. Solo Enterprise for kgateway adds enterprise features and support for production deployments.