### Redis backend

The service discovery has a plug-able backend using the `ServiceDiscoveryBackend` SPI. This is an implementation of the SPI based on Redis.

#### Using the Redis backend

To use the Redis backend, add the following dependency to the dependencies section of your build descriptor:

- Maven (in your `pom.xml`):

    <dependency>
     <groupId>io.vertx</groupId>
     <artifactId>vertx-service-discovery-backend-redis</artifactId>
     <version>4.0.2</version>
    </dependency>

- Gradle (in your `build.gradle` file):

    compile 'io.vertx:vertx-service-discovery-backend-redis:4.0.2'

Be aware that you can have only a single implementation of the SPI in your classpath. If none, the default backend is used.

#### Configuration

The backend is based on the vertx-redis-client. The configuration is the client configuration as well as `key` indicating in which key on Redis the records are stored.

Here is an example:

    ServiceDiscovery.create(vertx, new ServiceDiscoveryOptions()
        .setBackendConfiguration(
            new JsonObject()
                .put("connectionString", "redis://localhost:6379")
                .put("key", "records")
        ));

It’s important to note that the backend configuration is passed in the `setBackendConfiguration` method (or `backendConfiguration` entry if you use JSON):

    ServiceDiscovery.create(vertx,
      new ServiceDiscoveryOptions(new JsonObject()
        .put("backendConfiguration",
          new JsonObject().put("connectionString", "redis://localhost:6379").put("key", "my-records")
    )));