Splitting a system into multiple builds

§Splitting a system into multiple builds

For a small system maintained by a single team, it’s fine to have all your services in one build. Doing it that way makes it really easy to run all your services with the runAll task, as we’ll see later in the Running Services section of this manual.

If you have multiple teams, though, then as described already in Lagom build concepts, we recommend splitting your system into multiple builds.

If you aren’t concerned with scaling to multiple teams yet, feel free to skip this section for now.

§Publishing services

Even with multiple builds, you will still often want to run your services together in development. Lagom allows importing services published from one build into another build.

Suppose you have a helloworld service that you want to publish and import into another build:

organization in ThisBuild := "sample.helloworld"

scalaVersion in ThisBuild := "2.11.7"

lazy val helloworldApi = (project in file("helloworld-api"))
  .settings(version := "1.0")
  .settings(libraryDependencies += lagomJavadslApi)

lazy val helloworldImpl = (project in file("helloworld-impl"))
    version := "1.0",
    libraryDependencies += lagomJavadslPersistence

You can publish this to your local sbt repository by running publishLocal. This is the simplest way to publish a service, however, it means every developer that wants to run a build that imports the service will need to run publishLocal themselves on the service, and they’ll need to do that for each version that they want to import.

More commonly, many developers can share a single Maven or Ivy repository that they can publish and pull artifacts from. There are a few options for how to do this, if you’re happy to use a hosted repository, Bintray is a good option, if you want to run the repository locally, Artifactory or Nexus are common solutions. For information on how to configure these with sbt, see how to publish artifacts.

§Publishing to Bintray

Bintray offers both free open source hosting, as well as a paid private hosting service.

If you are using Bintray, the first thing you’ll need to do is sign up for an account, and create an organization. In your Bintray organization, you can then create a Bintray repository, we recommend creating a Maven repository.

Having set Bintray up, you now need to configure your sbt build to publish to this. First, add the sbt-bintray plugin to your project/plugins.sbt file:

addSbtPlugin("me.lessis" % "bintray-sbt" % "0.3.0")

The Bintray plugin manages its own credentials, this can be configured by running activator bintrayChangeCredentials, which will save the credentials in ~/.bintray/.credentials.

Once you’ve authenticated with Bintray, you can then configure your build to publish to it, by adding the following configuration to build.sbt:

// Set this to the organization that you want to publish to
bintrayOrganization in ThisBuild := Some("example-organization")
// This is needed for projects that are not open source
bintrayOmitLicense in ThisBuild := false

§Importing a service

The helloworld Lagom service can be imported by adding the following declaration to your build:

lazy val helloworld = lagomExternalProject("helloworld", "sample.helloworld" %% "helloworld-impl" % "1.0")

The first argument passed to lagomExternalProject is the name that will be used in your build to refer to this externally defined project. While, the second argument provides the dependency to the helloworld-impl JAR, using the conventional sbt syntax for declaring dependencies. Note in fact that the lagomExternalProject method returns a sbt Project, which you can further customize if needed.

After having added the external Lagom project to your build, just type reload in the sbt console. Then, when executing runAll, you should see that the helloworld service is started, together with all other services defined in the build:

> runAll
[info] ...
[info] Service helloworld listening for HTTP on 0:0:0:0:0:0:0:0:22407
[info] ...
(Services started, use Ctrl+D to stop and go back to the console...)

Now that you have integrated the helloworld service in your build, any of your Lagom projects can communicate with it after adding a library dependency to its helloworld-api artefact:

lazy val greetingsApi = (project in file("greetings-api"))
  .settings(libraryDependencies += lagomJavadslApi)

lazy val greetingsImpl = (project in file("greetings-impl")).enablePlugins(LagomJava)
  .settings(libraryDependencies += "sample.helloworld" %% "helloworld-api" % "1.0")

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.