service-discovery-with-etcd

NOTICE: THIS IS A DRAFT

Service Discovery With Etcd

The publisher publishes endpoint details for services to "the cloud". The configurator reads those details from "the cloud" and dynamically forwards to those services

RUNNING THE EXAMPLE

In this example we will start a self-publishing service that responds with "hello" that can be called from another service without knowledge of the endpoint

1. Download etcd: go to "https://github.com/coreos/etcd/releases/", scroll down to the "Downloads" section and pick the version for your operating system

2. Extract etcd in any directory and start etcd

3. In the membrane folder go to examples/service-discovery-with-etcd/

4. Execute configurator/start.bat

5. Open your favorite browser and go to localhost:9001, this opens the admin console of the configurator

6. Notice that "Console" is the only available service, "Console" is the admin console

7. Execute the publisher/start.bat

8. Open another tab in your browser and go to localhost:8081/myService and receive "hello" as response, this is a service from the publisher

9. Go back to the admin console window and refresh the page, another service should appear

10. Open another tab in your browser and go to localhost:8080/myService and receive hello as response, this is a service from the configurator

11. Exit the publisher.bat and wait 20 seconds.

12. Go back to the admin console window and refresh the page, the second service should disappear

HOW IT IS DONE

This section describes the example in detail.

First take a look at the proxies.xml file in the publisher folder.

<etcdPublisher baseUrl="http://localhost:4001" baseKey="/example" ttl="20"/>
<router>
  <serviceProxy name="helloResponse" port="8081">
    <path>/myService</path>
    <groovy>				
      exc.response = Response.ok("Hello").build()
      RETURN
    </groovy>
  </serviceProxy>
</router>

You will see that there is a service proxy that responds with hello when going to http://localhost:8081 in you browser. On top of that you can see the <etcdPublisher> that is responsible for publishing the endpoint details to an etcd.

The <etcdPublisher> element has 3 values that you can set and by default it is set to publish to a locally started etcd on "http://localhost:4001" every 5 minutes.

• baseUrl is the url the etcd is residing on
• baseKey is the directory where the endpoint details are saved
• ttl is how long in seconds the data in the etcd should be valid

Now take a look at the proxies.xml file in the configurator folder.

<etcdBasedConfigurator baseUrl="http://localhost:4001" baseKey="/example" port="8080"/>
<router>
<transport/>
  <serviceProxy name="Console" port="9001">
    <adminConsole />
  </serviceProxy>
</router>

You will see a service proxy that provides the admin console on port 9001. Additionally, on top you can see the etcdBasedConfigurator that reads from an etcd and creates service proxies for those services dynamically. The etcdBasedConfigurator has 3 values that you can set and by default it is set to read from an etcd on http://localhost:4001 and provides its service on port 8080.

• baseUrl is the url the etcd is residing on
• baseKey is the directory where the call details are saved
• port is the port the etcdBasedConfigurator provides its service on

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See:

• etcdBasedConfigurator reference
• etcdPublisher reference