#Leveraging Spring Cloud Consul for Discovery - CodeMash 2018

by David Lucas @DavidDLucas

• Instructions to setup and start consul
• Directory breakdown:
  • The docker folder has some examples of running a docker instance of consul
  • The local folder has scripts to download the consul binary (consul-binary-download.sh) and start it (consul-start-local.sh)
  • The load folder contains scripts to load / save key value pairs

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This example has a demo-service that have a /foo method and /hello/ method to demonstrate it is taking requests. This also using properties found under consul like "/config/application/foo with a value that will replace the default in the DemoController.

• If starting from scratch, add a REST controller and include the @Configuration, @EnableAutoConfiguration, @RefreshScope , @RestController .
• @RefreshScope is key to reloading properties from consul posting to Actuator's refresh endpoint
• Start the demo-service using ./mvnw spring-boot:run
• GET http://localhost:8080/hello to see the hello world message to include the default @Value.
• Now change / create a key (config/application/foo) / value (CodeMash Rocks) in consul at http://localhost:8500/ui under Key / Value tab and create / navigate to /config/application/foo
• Or you can create the key / value using curl curl -X PUT -d "CodeMash Rocks" http://localhost:8500/v1/kv/application/foo
• In order to refresh the properties in the service when they are changed in consul, one just needs to POST the refresh endpoint
• Example using curl: curl -s -X POST http://localhost:8080/application/refresh -o-
• There is a script (refresh.sh) that can be used to execute the refresh POST.

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This example is from the point of view of an application looking up the service and making a call. The actual code base just delegates its work to the original demo-service for a message.

• This example uses Kotlin and delegates to the "demo-service" by making a call via the Spring RestTemplate to "http://demo-service". Using the @LoadBalanced annotation on the RestTemplate @Bean creation will help it discover the host port behind the scene.
• Add to Demo Application class the @EnableDiscoveryClient (register) ( and optional @EnableFeignClients discovery for REST Template).
• Add to example REST controller @Configuration, @EnableAutoConfiguration, @RefreshScope, @RestController

This example is to show how to add the zuul server (a type of api gateway) to the mix.

• Annotations to add to enable gateway zuul server:
  • @EnableDiscoveryClient
  • @EnableFeignClients
  • @EnableZuulProxy

Please review the slides in the slides folder to read through what was attempted in the demo that might help understand. You can always reach out to me at @DavidDLucas or via github.com/lseinc issue.

slides/Spring-Cloud-Consul-CM2018.pdf

This will most likely change with the upcoming Spring Boot 2 release. But it should be close to how it will be without any major changes.

This is a work in progress. This is not a secure example and should be changed to secure actuator and provide authentication.

Enjoy!

2018-01-12