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What is an API proxy?

An API proxy acts like a mediator or go-between for the client and the API. It provides a central point of access to the API. It can add functionality to the API, such as security, caching, or rate limiting — and it can do it without requiring any changes to the API itself. The proxy can route requests to different backend services based on the request path or user, and it can perform tasks like authentication (e.g., key authentication, OAuth flows) and traffic management (e.g., rate limiting).

Common use cases for API proxies

Some common use cases for API proxies include:

• Request forwarding: The primary function of a proxy (including the API proxy) is to forward incoming requests to appropriate backends. In the case of an API proxy, it's an underlying API or service.
• Security: API proxies can be used to add a basic level of security to an API.
• Caching: API proxies can be used to cache responses from an API, reducing the response time for subsequent requests and improving overall performance.
• Load balancing: API proxies can provide load-balancing functionality by routing requests to the appropriate backend server based on factors such as server load, network latency, or geographic location.
• SSL termination: API proxies can handle SSL termination on behalf of the underlying APIs.

API proxy vs API gateway

Both the API proxy and the API gateway sit in front of your existing APIs, acting like gatekeepers, but with a big difference in capabilities. In most cases, an API gateway can do everything the API proxy does and more.

So, when should we use a proxy to expose our APIs and when we should use an API gateway? The answer to that question depends on a few factors:

• How many APIs are you planning to expose?
• Are the APIs going to be exposed externally (over the internet) or just internally to your organization?
• What functionality do you want your proxy or gateway to handle on behalf of your APIs?
• How much importance do you place on developer experience?

Advantage of API gateways over API proxies

API proxies are useful when you want to add a very specific (and simple) functionality to an existing API, while API gateways are useful when you want to manage and secure multiple APIs in a centralized manner.

An API proxy is generally a much simpler proxy that forwards API requests from clients to backend APIs, while an API gateway is something that provides more advanced features and a centralized platform to manage multiple APIs.

Some of the key advantages of an API gateway over an API Proxy are:

• Advanced API features, including full lifecycle management: API gateways provide a more comprehensive set of features to help organizations manage a full lifecycle of an API from the initial development stage (e.g., mocking services) to version control as well as request/response transformation.
• Advanced security: Although API proxies may offer basic security features for an API, API gateways offer many more features when it comes to security, including integrating with existing IDPs in an organization and the ability to handle OAuth flows and JWT tokens.
• Developer experience: When it comes to exposing APIs either externally to customers/partners or internally within an organization, API gateways have a range of features that enhance the developer experience, including things like specialized developer portals that can be used to expose API specs, handling the registration of developer applications, giving the ability to try out exposed APIs, and more.

What is a reverse proxy?

A reverse proxy sits between a client and a web server by handling the request and response on behalf of the server. It intercepts requests from the client and forwards them to the appropriate backend server and sends the corresponding responses back to the client. It can also provide additional features such as load balancing, caching, and security.

The way reverse proxies work can be thought of as the following sequence of steps that detail what happens from the initial request from a client to the final response from a web server that goes through a reverse proxy:

1. The client initially sends a request to a web server. Unknown to the client, this request instead is intercepted by the reverse proxy as it's acting on behalf of the server.
2. The reverse proxy checks the request to determine where to forward the request. It may use load-balancing algorithms to determine which server to send the request to.
3. The reverse proxy forwards the request to the appropriate server.
4. The server processes the request and generates a response and sends the response back to the reverse proxy.
5. The reverse proxy receives the response and can optionally perform additional processing such as caching, filtering, or modifying the response.
6. The reverse proxy sends the response back to the client as if it came from the original server.

Common use cases of a reverse proxy

• Load balancing: A reverse proxy can distribute incoming traffic across multiple backend servers to improve the performance, availability, and scalability of the application.
• SSL/TLS termination: A reverse proxy can handle SSL/TLS encryption and decryption on behalf of the backend web server.
• Compression: A reverse proxy can compress the content being transmitted, reducing the bandwidth required and improving performance.
• Caching: A reverse proxy can cache frequently accessed content to reduce the load on the backend servers which leads to an improvement in response times.
• Security: A reverse proxy can provide an additional layer of security by filtering and blocking malicious traffic, limiting access to certain resources, and enforcing authentication and authorization policies.

API gateway vs reverse proxy

Both API gateways and reverse proxies have overlapping features, but they both serve different purposes. While the API gateway acts like the front door to your underlying APIs, a reverse proxy is the front door to your web applications.

When it comes to functionality, API gateways are tailored for API management, and hence the functionality they offer are:

• API versioning and transformation
• Authentication and authorization (e.g., OAuth, JWT, and other api authentication types)
• Rate limiting and throttling
• Caching
• Logging and API monitoring
• Request/response transformation
• Service discovery
• Circuit breaker and fault tolerance

Reverse proxies, on the other hand, offer a more generalized feature set that can be applied to any type of web service be it an API or a web server. The functionality includes things like:

• Load balancing
• SSL offloading/termination
• Caching
• Compression
• URL rewriting
• Security features (e.g., filtering malicious requests, handling DDoS attacks)

In terms of setting up and configuration, API gateways often require more setup and maintenance than a reverse proxy due to a more extensive feature set. To get an API gateway up and running, you generally need to define routes to your underlying APIs, set up authentication, and configure other API-related policies. A reverse proxy on the other hand can be set up in a much simpler way.

Advantages of an API gateway over a reverse proxy

API gateways provide more advanced features compared to a reverse proxy especially when it comes to the management of APIs. Some of the key benefits include:

• Developer experience: API gateways often provide a much better experience to both internal and external developers that enhances the use of the underlying APIs. These features could include a developer portal, registration facility, and mock responses.
• API-specific advanced features: An API gateway provides advanced features for managing the full lifecycle of an API. Some of the features that aren't available in reverse proxies include:
  • API lifecycle management including version control
  • Authentication/authorization, including integration with existing IDP systems
  • Rate limiting or throttling based on tiers
  • Simple transformation in request/response
• Centralized API management: Although reverse proxies and API gateways both may act as a single point for access to your APIs, when it comes to managing and controlling all your APIs consistently, API gateways provide a much greater level of control. They make it easier to enforce policies, monitor usage, and maintain consistency across all the different services.

Conclusion

The key to choosing between an API gateway, API proxy, or a reverse proxy is to look at the underlying use case:

If the primary goal is to manage multiple APIs in a standardized way with full lifecycle management and enhanced developer experience, then you need all the advanced features that an API gateway provides. However, if you're looking for a general-purpose solution for handling web traffic, then a reverse proxy might be more appropriate.