This is a small API Gateway demo using Spring Cloud Gateway. It was done for my talk at CodeMash 2024, slides.

There are some client templates set up using Bruno, you can open them or just look at the text and make your own requests. Any tool like curl or Postman will work just fine.

If you want to run and check out the Facade Pattern, run ./gradlew bootRun.

This will expose two endpoints /give-me-dogs and /give-me-cats which will return a list of dogs and cats respectively. They point to the services https://dog.ceo and https://cataas.com/.

This demo shows the facade pattern and how you put a unique interface in front of the two APIs without modifying the APIs. See the application-facade.yml file for specifics on how SCG was configured.

Highlights:

• we change the paths around
• we add some request params
• we rewrite one of the endpoint's response
• we reformat one of the request URIs

This one is a little more difficult to demo, but it's been enabled for all of the demos here. It allows us to spy on requests and capture some metrics about them. You can then use the Spring Boot Actuator Metrics endpoint to examine them or you can hook things up to your metrics system, like Prometheus.

In addition, by adding one system property to the application we can enable access logging which is a great thing to have in production. This is done by adding the system flag -Dreactor.netty.http.server.accessLogEnabled=true. In this demo, it's added in build.gradle, but it could be added anywhere you normally add your JVM flags.

bootRun {
    // enables Netty access logging
    jvmArgs(['-Dreactor.netty.http.server.accessLogEnabled=true'])
}

With it enabled, you'll get lines like:

2024-01-10T15:48:19.020-05:00  INFO 32005 --- [ctor-http-nio-2] reactor.netty.http.server.AccessLog      : 0:0:0:0:0:0:0:1 - - [10/Jan/2024:15:48:18 -0500] "GET /give-me-cats HTTP/1.1" 200 161 1017

These could be fed into your log aggregation system for further analysis.

In the Facade demo, we saw how we could rewrite the response from one of the APIs. This is being done in RewriteDogJsonGatewayFilterFactory. The code uses Jackson to parse the JSON response from the upstream API and then rewrites it to a new JSON response. This is a very simple example, but it shows how you can transform the response.