Development Environment

§Development Environment

Lagom’s sbt and Maven based development environments allow running any number of services together with a single command.

The same command also reloads your services when the code changes, so that you don’t have to manually restart them. You can stay focused on your work and let Lagom do the compiling and reloading.

§Running all services in Maven

To run all services in Maven, simply run the lagom:runAll command:

$ cd <path to your Lagom project>
$ mvn lagom:runAll
INFO ...
INFO Service hello-impl listening for HTTP on 0:0:0:0:0:0:0:0:23966
INFO Service hello-stream-impl listening for HTTP on 0:0:0:0:0:0:0:0:27462
(Services started, press enter to stop and go back to the console...)

This may take a while if you have a lot of services or if dependencies are being retrieved for the first time.

§Starting the sbt development console

Assuming you have an sbt project, it’s now time to fire up the console on your Lagom project directory:

$ cd <path to your Lagom project>
$ sbt
[info] ...
>

To run all Lagom services together, with automatic reloading, just enter runAll in the sbt console:

> runAll
[info] ...
[info] Service hello-impl listening for HTTP on 0:0:0:0:0:0:0:0:23966
[info] Service stream-impl listening for HTTP on 0:0:0:0:0:0:0:0:27462
(Services started, press enter to stop and go back to the console...)

This may take a while if you have a lot of services or if dependencies are being retrieved for the first time.

§Hot reloading

Once the “Services started” message has appeared, if you make a change to your source code, you’ll see output like this in the console:

[info] Compiling 1 Java source to /<project-path>/target/scala-2.12/classes...

--- (RELOAD) ---

§Managing custom services

By default, Lagom will, in addition to running your services, also start a service locator, a Cassandra server and a Kafka server. If using sbt, you can customize what Lagom starts, including adding other databases and infrastructure services.

Note: Managing custom services is not currently supported in Maven, due to Maven’s inability to arbitrarily add behaviour, such as the logic necessary to start and stop an external process, to a build. This is typically not a big problem, it simply means developers have to manually install, start and stop these services themselves.

To add a custom service, first you need to define a task to start the service in your build.sbt. The task should produce a result of Closeable, which can be used to stop the service. Here’s an example for Elastic Search:

import java.io.Closeable

val startElasticSearch = taskKey[Closeable]("Starts elastic search")

startElasticSearch in ThisBuild := {
  val esVersion = "5.4.0"
  val log = streams.value.log
  val elasticsearch = target.value / s"elasticsearch-$esVersion"

  if (!elasticsearch.exists()) {
    log.info(s"Downloading Elastic Search $esVersion...")
    IO.unzipURL(url(s"https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-$esVersion.zip"), target.value)
    IO.append(elasticsearch / "config" / "log4j2.properties", "\nrootLogger.level = warn\n")
  }

  val binFile = if (sys.props("os.name") == "Windows") {
    elasticsearch / "bin" / "elasticsearch.bat"
  } else {
    elasticsearch / "bin" / "elasticsearch"
  }

  val process = Process(binFile.getAbsolutePath, elasticsearch).run(log)
  log.info("Elastic search started on port 9200")

  new Closeable {
    override def close(): Unit = process.destroy()
  }
}

Now we’re able to start Elastic Search, we need to add this task to Lagom’s list of infrastructure services, so that Lagom will start it when runAll is executed. This can be done by modifying the lagomInfrastructureServices setting:

lagomInfrastructureServices in ThisBuild += (startElasticSearch in ThisBuild).taskValue

§Behind the scenes

What’s happening behind the scenes when you runAll?

This all happens automatically without special code or additional configuration.

You can verify that your services are running by viewing http://localhost:9008/services in a web browser (or with a command line tool such as curl). The Service Locator, running on port 9008, will return JSON such as:

[{"name":"hello-stream","url":"http://0.0.0.0:26230"},
 {"name":"cas_native","url":"tcp://127.0.0.1:4000/cas_native"},
 {"name":"hello","url":"http://0.0.0.0:24266"}]

cas_native is the Cassandra server. As you will learn in the documentation for writing persistent and clustered services, Cassandra is the default database in Lagom, and it’s an integral part of the development environment.

The Service Locator, Cassandra, and Kafka are covered in more detail in the sections that follow.

Found an error in this documentation? The source code for this page can be found here. Please feel free to edit and contribute a pull request.