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08 - Build a Spring Cloud Gateway

This guide is part of the Azure Spring Apps training

A Spring Cloud gateway allows you to selectively expose your microservices and to route traffic to them and among them. In this section, we will create a Spring Cloud Gateway that will expose the microservices we created in the preceding two sections.

Create a Spring Cloud Gateway

The application that we create in this guide is available here.

To create our gateway, we will invoke the Spring Initalizr service from the command line:

curl https://start.spring.io/starter.tgz -d type=maven-project -d dependencies=cloud-gateway,cloud-eureka,cloud-config-client -d baseDir=gateway -d bootVersion=3.1.3 -d javaVersion=17 | tar -xzvf -

We use the Cloud Gateway, Eureka Discovery Client and the Config Client components.

Configure the application

Rename src/main/resources/application.properties to src/main/resources/application.yml and add the following configuration:

spring:
  cloud:
    gateway:
      discovery:
        locator:
          enabled: true
      globalcors:
        corsConfigurations:
          '[/**]':
            allowedOrigins: "*"
            allowedMethods:
              - GET
  • The spring.cloud.gateway.discovery.locator.enabled=true part is to configure Spring Cloud Gateway to use the Spring Cloud Service Registry to discover the available microservices.
  • The spring.cloud.gateway.globalcors.corsConfiguration part is to allow Cross-Origin Resource Sharing (CORS) requests to our gateway. This will be helpful in the next guide, when we will add a front-end that is not hosted on Azure Spring Apps.

Create the application on Azure Spring Apps

As in 02 - Build a simple Spring Boot microservice, create a specific gateway application in your Azure Spring Apps instance. As this application is a gateway, we add the --assign-endpoint true flag so it is exposed publicly.

az spring app create -n gateway --runtime-version Java_17 --assign-endpoint true

Deploy the application

You can now build your "gateway" project and send it to Azure Spring Apps:

cd gateway
./mvnw clean package -DskipTests
az spring app deploy -n gateway --artifact-path target/demo-0.0.1-SNAPSHOT.jar
cd ..

Test the project in the cloud

  • Go to "Apps" in your Azure Spring Apps instance.
    • Verify that gateway has a Registration status which says 1/1. This shows that it is correctly registered in the Spring Cloud Service Registry.
    • Select gateway to have more information on the microservice.
  • Copy/paste the public URL that is provided (there is a "Test endpoint" like for microservices, but the gateway is directly exposed on the Internet, so let's use the public URL). Keep this URL handy for subsequent sections.

As the gateway is connected to the Spring Cloud Service Registry, it should have automatically opened routes to the available microservices, with URL paths in the form of /MICROSERVICE-ID/**.

🛑 The MICROSERVICE-ID must be uppercase, all CAPS. Replace XXXXXXXX with the name of your Azure Spring Apps instance.

  • Test the city-service microservice endpoint: 
    curl https://XXXXXXXX-gateway.azuremicroservices.io/CITY-SERVICE/cities
  • Test the weather-service microservice endpoint by doing: 
    curl 'https://XXXXXXXX-gateway.azuremicroservices.io/WEATHER-SERVICE/weather/city?name=Paris%2C%20France'

If you need to check your code, the final project is available in the "gateway" folder.

⬅️ Previous guide: 07 - Build a Spring Boot microservice using MySQL

➡️ Next guide: 09 - Putting it all together, a complete microservice stack