BernhardBln / snowizard-discovery

Service discovery for Snowizard using Curator

Snowizard Discovery

This is a Dropwizard bundle that can be used to register a Dropwizard service into Zookeeper upon startup. Connectivity to Zookeeper is provided by Netflix's Curator library and its built in Service Discovery framework.

Usage

To use the snowizard-discovery module, first add it as a dependency into your Maven pom.xml file:

<dependencies>
    <dependency>
        <groupId>com.ge.snowizard</groupId>
        <artifactId>snowizard-discovery</artifactId>
        <version>0.7.0</version>
    </dependency>
</dependency>

Then in your Dropwizard Configuration file, add a property to represent the discovery configuration for your service:

# Discovery-related settings.
discovery:
    serviceName: hello-world

And have your configuration class expose the DiscoveryFactory.

public class HelloWorldConfiguration extends Configuration {

    @Valid
    @NotNull
    private DiscoveryFactory discovery = new DiscoveryFactory();

    @JsonProperty("discovery")
    public DiscoveryFactory getDiscoveryFactory() {
        return discovery;
    }

    @JsonProperty("discovery")
    public void setDiscoveryFactory(final DiscoveryFactory discoveryFactory) {
        this.discovery = discoveryFactory;
    }
}

If you only wish to have your service register itself with Zookeeper and you don't intend on consuming any other services, you just need to add the following into your service's initialize method:

public class HelloWorldApplication extends Application<HelloWorldConfiguration> {

    private final DiscoveryBundle<HelloWorldConfiguration> discoveryBundle = new DiscoveryBundle<HelloWorldConfiguration>() {
        @Override
        public DiscoveryFactory getDiscoveryFactory(final HelloWorldConfiguration configuration) {
            return configuration.getDiscoveryFactory();
        }
    };

    @Override
    public void initialize(Bootstrap<HelloWorldConfiguration> bootstrap) {
        bootstrap.addBundle(discoveryBundle);
    }
}

where HelloWorldConfiguration is your configuration class name.

If you want to also consume other services, you can store an instance of the DiscoveryBundle so that you can retrieve a new DiscoveryClient to access additional services.

public class HelloWorldApplication extends Application<HelloWorldConfiguration> {

    private final DiscoveryBundle<HelloWorldConfiguration> discoveryBundle = new DiscoveryBundle<HelloWorldConfiguration>() {
        @Override
        public DiscoveryFactory getDiscoveryFactory(final HelloWorldConfiguration configuration) {
            return configuration.getDiscoveryFactory();
        }
    };

    @Override
    public void initialize(Bootstrap<HelloWorldConfiguration> bootstrap) {
        bootstrap.addBundle(discoveryBundle);
    }

    @Override
    public void run(HelloWorldConfiguration configuration, Environment environment) throws Exception {
        final DiscoveryClient client = discoveryBundle.newDiscoveryClient("hello-world");
        environment.lifecycle().manage(new DiscoveryClientManager(client));
    }
}

Be sure to register the DiscoveryClient using the DiscoveryClientManager as a Managed Object so that it is properly started and shutdown when your service is stopped and started.

Enhancements

1. Support an "Advertise Locally, Lookup Globally" model that Camille Fournier outlined on her blog by supporting separate Zookeeper connections, one that connects locally and one that connects to a global instance.

Contributing

To contribute:

1. fork the project
2. make a branch for each thing you want to do (don't put everything in your master branch: we don't want to cherry-pick and we may not want everything)
3. send a pull request to jplock

Building

To build and test, run mvn test.