AzkarraApplication

The AzkarraApplication is the top-level concept that is used to bootstrap an Azkarra Streams application.

Its main responsibility is to initialize an AzkarraContext using a user-defined configuration which describes the StreamsExecutionEnvironments and the streams applications to be executed.

The AzkarraApplication is also responsible for deploying an embedded HTTP server (if enable)

5.1 Creating a new AzkarraApplication

AzkarraApplication application = new AzkarraApplication();

5.2 Auto-configuration application

The AzkarraApplication allows you to automatically configure and assemble the internal AzkarraContext, StreamsExecutionEnvironment and TopologyProvider instances using the AzkarraConf class.

AzkarraConf azkarraConf = AzkarraConf.create("application");
AzkarraApplication application = new AzkarraApplication()
        .setConfiguration(azkarraConf);

5.2.1 Configuring AzkarraContext

azkarra {
  // The context configuration
  context {
    // The default configuration for streams application.
    streams {
      bootstrap.servers = "localhost:9092"
      default.key.serde = "org.apache.kafka.common.serialization.Serdes$StringSerde"
      default.value.serde = "org.apache.kafka.common.serialization.Serdes$StringSerde"
    }
  }
  ...
}

5.2.2 Configuring components to register

Complete example (using HOCON format):

azkarra {
  ...	
  // Manually defines the providers to be registered
  components = [
    io.streamthoughts.azkarra.example.topology.WordCountTopology
  ]

}

5.2.3 Configuring StreamsExecutionEnvironment and TopologyProvider

The azkarra.environments property allows you to list the StreamsExecutionEnvironment to initialize and configure.

Here are the properties to use:

Moreover, you can declared the list of TopologyProvider to be registered into a StreamsExecutionEnvironment using the following properties:

azkarra {
  ...	
  // Create a default environment for running the WordCountTopology
  environments = [
    {
      name: "__default"
      config = {}
      jobs = [
        {
          name = "word-count-demo"
          description = "Kafka Streams WordCount Demo"
          topology =  "WordCountTopology"
          config = {}
        }
      ]
    }
  ]
}

5.2.4 Configuring embedded http-server

azkarra {
  ...	
  server {
    listener = localhost
    port = 8080
    headless = false
    // These information will be exposes through the http endpoint GET /info
    info {
      app {
        name = "@project.name@"
        description = "@project.description@"
        version = "@project.version@"
        encoding = "@project.build.sourceEncoding@"
        java.version = "@java.version@"
      }
    }
  }
}

5.3 Enabling component-scan

Azkarra provides a simple mechanism to search for components present in the classpath or in external directories.

Any class annotated with @Component or @Factory will be scanned and automatically registered to the AzkarraContext.

The component-scan can be enable programmatically through the method AzkarraApplication#setEnableComponentScan. To automatically start all registered TopologyProviver, you must also enable auto-start.

Code snippet for enabling component scan :

application.setEnableComponentScan(true);

5.4 Auto-starting topologies

By enabling auto-start all TopologyProvider that was registered during component-scanning will be automatically added to the given StreamExecutionEnvironment.

application.setAutoStart(true, "__default");

5.5 Enabling embedded HTTP server

Azkarra packs with an embedded HTTP server (based on Undertow) which exposes REST endpoints, allowing you to manage registered topologies and to run streams instances.

application.enableHttpServer(true, HttpServerConf.with("localhost", 8080))

Note that when you enable the HTTP-server, Azkarra automatically configures the application.server property for running KafkaStreams instances.

5.6 The @AzkarraStreamsApplication annotation

Another way to initialize and configure an AzkarraApplication is to use annotations. Therefore, you can simply annotated you main class with @AzkarraStreamsApplication and initialize your AzkarraApplication as follows:

@AzkarraStreamsApplication
public class SimpleStreamsApp {

    public static void main(final String[] args) {
        AzkarraApplication.run(SimpleStreamsApp.class, args);
    }
}

The @AzkarraStreamsApplication is a convenience annotation that adds all of the following:

• @EnableAutoConfig: Tells Azkarra to auto-configure internal AzkarraContext
• @EnableAutoStart: Tells Azkarra to automatically start any registered TopologyProvider using the default environment.
• @EnableEmbeddedHttpServer: Tells Azkarra to start the embedded http-server.
• @ComponentScan: Tells Azkarra to look for classes annotated with @Component in the current package.