A typical cloud application consists of different services that communicate with each other. Because of the cloud’s nature servers come and go and therefore the location of a service (the IP address) will change. Service Discovery allows services to know each other. One way is to set up a service registry where every service can register. Other services can look up the service registry information, get the location and are able to connect to this service directly. A possible implementation of a service registry is Eureka from Netflix.
Spring Boot makes it easy to create stand-alone Spring based applications and with Spring Cloud Netflix it provides an integration of Netflix OSS. In the following I will show a simple setup of a Eureka server with a client in Pivotal Cloud Foundry.
It is really easy to use Eureka with Spring Boot. The first thing you need to start is obviously the server:
In application.yml only the application name and the default zone need to be set. The name will be used to register and the defaultZone is the URL of the Eureka server. For a local setup this will be http://127.0.0.1:8761/eureka/.
If you start both applications, the logs show that the testApp registers its instance:
Registered instance TESTAPP/172.16.177.147:testApp with status UP
Eureka comes with a built-in web UI where it shows all registered services. Go to http://127.0.0.1:8761 to see the registered instance of testApp:
Now that the local setup is running, let’s take it to the cloud!
The simplest way to deploy an application to Cloud Foundry is to upload the Jar file directly in Cloud Foundry’s web frontend. But this has some disadvantages. The configuration must be done manually and probably the biggest disadvantage: It is not automated!
Congratulations, you have deployed your Eureka server to Cloud Foundry! To verify this, go to http://eureka-test-service.cfapps.io and have a look at the web UI of Eureka.
A service registry without clients is pointless. Therefore the next step is to configure our testApp to use Eureka in the cloud. The easiest way would be to set the default zone to http://eureka-test-service.cfapps.io/eureka/, but this would bind the application to this single instance. If the URL changes you have to recompile the application. Instead of storing environment specific configuration in the application, the environment should provide the URL (see http://12factor.net/config). An easy way to provide the URL via an environment variable is a user provided service.
To enable an application to use a service in Cloud Foundry you have to bind the service to the application.
If the service is bound to our application it will provide the Eureka URL in the environment variable vcap.services.eureka.credentials.url. To use this in the testApp add a cloud specific spring profile to application.yml and set the defaultZone:
The hostname is set to vcap.application.uris. This variable is provided by Cloud Foundry and contains the public URL of an application. This URL will be used to register with Eureka. Other services can then retrieve this URL from Eureka to connect to testApp.
Just as the server project has a manifest.yml, so the testApp will have one:
The active spring profile is selected with the environment variable spring.profiles.active: cloud which can be set in the env attribute.
The service eureka is bound to this application in the services block.
The complete manifest.yml should look like this:
- name: testApp
Deploy it to Cloud Foundry
As usual first build the jar: mvn clean install
Now push it to Cloud Foundry via CLI: cf push
The logs show the registration of the Eureka client with the Eureka server.
On the UI http://eureka-test-service.cfapps.io you can see that TESTAPP is registered.
That’s it! Within a few simple steps you have created a service registry with Spring Boot. First a Eureka server and client for a local setup, then configured both to be cloud ready and deployed them to Cloud Foundry.