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Ilkka Seppälä
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api-gateway/README.md
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## Intent
The API Gateway design pattern aims to provide a unified interface to a set of microservices. It acts as a single entry point for clients, routing requests to the appropriate microservices and aggregating results, thereby simplifying the client-side code.
The API Gateway design pattern aims to provide a unified interface to a set of microservices. It acts as a single entry
point for clients, routing requests to the appropriate microservices and aggregating results, thereby simplifying the
client-side code.
## Also known as
@@ -19,47 +21,47 @@ The API Gateway design pattern aims to provide a unified interface to a set of m
## Explanation
With the Microservices pattern, a client may need data from multiple different microservices. If the
client called each microservice directly, that could contribute to longer load times, since the
client would have to make a network request for each microservice called. Moreover, having the
client call each microservice directly ties the client to that microservice - if the internal
implementations of the microservices change (for example, if two microservices are combined sometime
in the future) or if the location (host and port) of a microservice changes, then every client that
With the Microservices pattern, a client may need data from multiple different microservices. If the
client called each microservice directly, that could contribute to longer load times, since the
client would have to make a network request for each microservice called. Moreover, having the
client call each microservice directly ties the client to that microservice - if the internal
implementations of the microservices change (for example, if two microservices are combined sometime
in the future) or if the location (host and port) of a microservice changes, then every client that
makes use of those microservices must be updated.
The intent of the API Gateway pattern is to alleviate some of these issues. In the API Gateway
pattern, an additional entity (the API Gateway) is placed between the client and the microservices.
The job of the API Gateway is to aggregate the calls to the microservices. Rather than the client
calling each microservice individually, the client calls the API Gateway a single time. The API
The intent of the API Gateway pattern is to alleviate some of these issues. In the API Gateway
pattern, an additional entity (the API Gateway) is placed between the client and the microservices.
The job of the API Gateway is to aggregate the calls to the microservices. Rather than the client
calling each microservice individually, the client calls the API Gateway a single time. The API
Gateway then calls each of the microservices that the client needs.
Real world example
> We are implementing microservices and API Gateway pattern for an e-commerce site. In this system
> We are implementing microservices and API Gateway pattern for an e-commerce site. In this system
> the API Gateway makes calls to the Image and Price microservices.
In plain words
> For a system implemented using microservices architecture, API Gateway is the single entry point
> that aggregates the calls to the individual microservices.
> For a system implemented using microservices architecture, API Gateway is the single entry point
> that aggregates the calls to the individual microservices.
Wikipedia says
> API Gateway is a server that acts as an API front-end, receives API requests, enforces throttling
> and security policies, passes requests to the back-end service and then passes the response back
> to the requester. A gateway often includes a transformation engine to orchestrate and modify the
> requests and responses on the fly. A gateway can also provide functionality such as collecting
> analytics data and providing caching. The gateway can provide functionality to support
> API Gateway is a server that acts as an API front-end, receives API requests, enforces throttling
> and security policies, passes requests to the back-end service and then passes the response back
> to the requester. A gateway often includes a transformation engine to orchestrate and modify the
> requests and responses on the fly. A gateway can also provide functionality such as collecting
> analytics data and providing caching. The gateway can provide functionality to support
> authentication, authorization, security, audit and regulatory compliance.
**Programmatic Example**
This implementation shows what the API Gateway pattern could look like for an e-commerce site. The
`ApiGateway` makes calls to the Image and Price microservices using the `ImageClientImpl` and
`PriceClientImpl` respectively. Customers viewing the site on a desktop device can see both price
information and an image of a product, so the `ApiGateway` calls both of the microservices and
aggregates the data in the `DesktopProduct` model. However, mobile users only see price information;
they do not see a product image. For mobile users, the `ApiGateway` only retrieves price
This implementation shows what the API Gateway pattern could look like for an e-commerce site. The
`ApiGateway` makes calls to the Image and Price microservices using the `ImageClientImpl` and
`PriceClientImpl` respectively. Customers viewing the site on a desktop device can see both price
information and an image of a product, so the `ApiGateway` calls both of the microservices and
aggregates the data in the `DesktopProduct` model. However, mobile users only see price information;
they do not see a product image. For mobile users, the `ApiGateway` only retrieves price
information, which it uses to populate the `MobileProduct`.
Here's the Image microservice implementation.
@@ -153,7 +155,8 @@ public class ApiGateway {
## Applicability
* When building a microservices architecture, and there's a need to abstract the complexity of microservices from the client.
* When building a microservices architecture, and there's a need to abstract the complexity of microservices from the
client.
* When multiple microservices need to be consumed in a single request.
* For authentication, authorization, and security enforcement at a single point.
* To optimize communication between clients and services, especially in a cloud environment.
@@ -181,9 +184,12 @@ Trade-offs:
## Related patterns
* [Aggregator Microservice](../aggregator-microservices/README.md) - The API Gateway pattern is often used in conjunction with the Aggregator Microservice pattern to provide a unified interface to a set of microservices.
* [Proxy](../proxy/README.md) - The API Gateway pattern is a specialized form of the Proxy pattern, where the gateway acts as a single entry point for clients, routing requests to the appropriate microservices and aggregating results.
* [Circuit Breaker](../circuit-breaker/README.md) - API Gateways can use the Circuit Breaker pattern to prevent cascading failures when calling multiple microservices.
* [Aggregator Microservice](../aggregator-microservices/README.md) - The API Gateway pattern is often used in
conjunction with the Aggregator Microservice pattern to provide a unified interface to a set of microservices.
* [Proxy](../proxy/README.md) - The API Gateway pattern is a specialized form of the Proxy pattern, where the gateway
acts as a single entry point for clients, routing requests to the appropriate microservices and aggregating results.
* [Circuit Breaker](../circuit-breaker/README.md) - API Gateways can use the Circuit Breaker pattern to prevent
cascading failures when calling multiple microservices.
## Tutorials