TimMoore / lagom-mvn-standalone

lagom-mvn-standalone

A basic example of building a Lagom project to run standalone, without the use of ConductR, Kubernetes, or another managed platform.

Warning: this is outdated and not suitable for use in production. See Caveats below for more information.

This was initially created from the Lagom Java Maven archetype (mvn archetype:generate -DarchetypeGroupId=com.lightbend.lagom -DarchetypeArtifactId=maven-archetype-lagom-java -DarchetypeVersion=1.2.2), with the following changes:

• Removed ConductR-specific configuration
• Added basic start scripts, based on the template provided in Lagom's "Using ConductR with Maven" documentation
• Modified the assembly descriptors to create a simplified layout, with the start script directly in bin and all library dependencies in lib
• Added ConfigurationServiceLocator to Guice modules in each implementation project, as described in the Lagom documentation
• Added static port bindings to each service (hello-impl: 8001, stream-impl: 8002)
• Added a static service location to hello-impl for cas_native (the Cassandra server)
• Added a static service location to stream-impl for hello

To test this:

1. Open a terminal and clone the repository to your workstation (git clone https://github.com/TimMoore/lagom-mvn-standalone.git)
2. cd lagom-mvn-standalone
3. mvn package to create distribution packages
4. Start a Cassandra server on port 4000. There are a few ways to do this:

   1. Get an sbt-based Lagom project (such as lagom-sbt-standalone) and run sbt lagomCassandraStart in its root directory

   2. Run Cassandra in Docker: docker run --rm --name cassandra -p4000:9042 -d cassandra:latest

   3. Download and run Cassandra standalone as described in the Cassandra Getting Started guide

      Note that you'll need to either configure Cassandra to run on port 4000, or change the cas_native service locator configuration in hello-impl/src/main/resources/application.conf

5. Open two more terminals in the lagom-mvn-standalonedirectory
6. In one terminal:
   1. cd hello-impl/target/
   2. unzip hello-impl-1.0-SNAPSHOT-standalone-bundle.zip (or, if you don't have the unzip command, use any tool to unzip the file into the same directory)
   3. cd hello-impl-1.0-SNAPSHOT
   4. bin/hello-impl (the equivalent on Windows is left as an exercise for the reader 😄)
7. In the other terminal:
   1. cd stream-impl/target/
   2. unzip stream-impl-1.0-SNAPSHOT-standalone-bundle.zip
   3. cd stream-impl-1.0-SNAPSHOT
   4. bin/stream-impl

This runs each of the services on the configured port, as single-node clusters.

You can press control-C to exit the services.

Caveats

This configuration is not suitable for production deployments, it's just intended as a starting point. Here are some of the limitations to be aware of.

• Static service locator configuration is difficult to manage in practice, as it requires configuration to be duplicated across all services, and configuring additional services requires a restart.
• The provided ConfigurationServiceLocator only supports a single endpoint per service, which reduces resilience and elasticity.
• These start scripts use -Dlagom.cluster.join-self=on, which restricts each service to run on a single node. Creating a multi-node cluster requires configuring seed nodes as described in the Lagom Cluster documentation. Running more than one instance of this service will cause data corruption.
• The provided launcher scripts do not attempt to handle process supervision or health monitoring