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Ilkka Seppälä
2020-08-10 16:25:06 +03:00
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api-gateway/README.md
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@@ -12,49 +12,53 @@ tags:
## Intent
Aggregate calls to microservices in a single location: the API Gateway. The user makes a single call to the API Gateway,
and the API Gateway then calls each relevant microservice.
Aggregate calls to microservices in a single location, the API Gateway. The user makes a single call
to the API Gateway, and the API Gateway then calls each relevant microservice.
## 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 Gateway then calls each of the microservices that the client needs.
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 the API Gateway makes
calls to the Image and Price microservices.
> 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 authentication, authorization, security, audit and regulatory compliance.
> 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 information, which
it uses to populate the `MobileProduct`.
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.
@@ -64,7 +68,6 @@ public interface ImageClient {
}
public class ImageClientImpl implements ImageClient {
@Override
public String getImagePath() {
var httpClient = HttpClient.newHttpClient();
@@ -114,7 +117,7 @@ public class PriceClientImpl implements PriceClient {
}
```
And here we can see how API Gateway maps the requests to the microservices.
Here we can see how API Gateway maps the requests to the microservices.
```java
public class ApiGateway {