I am working on developing a rules engine designed to handle ISO20022 standard payment (SWIFT) and securities messages. It handles parsing, validation and enrichment of message and provides business users access to these features via a simple English like DSL. More about this later.
I had been deploying to virtual machines on the cloud, but wanted a solution that was more cost effective and scalable. Cloud Run is a service by Google Cloud Platform to run your stateless HTTP containers without worrying about provisioning machines, clusters or autoscaling. The first step was to dockerize my application. It turned out that dockerizing a Scala application is pretty easy
SBT Setup
-
Add the SBT native packager to project/plugins.sbt. This lets you build application packages in native formats
addSbtPlugin("com.typesafe.sbt" % "sbt-native-packager" % "1.7.5") -
Package your application and create launch scripts using the Java app packaging plugin
enablePlugins(JavaAppPackaging) -
Ask SBT to build Docker images. You will need a Docker client has to be installed**
enablePlugins(DockerPlugin) -
Build and publish your image
sbt docker:publishLocal -
Take it for a spin
docker run --rm -p8080:8080 payment-rules:1.0
Customisation
This should work out of the box, but you can customise each step
Customise the packaging and launch scripts (e.g. setting environment variables or JVM parameter using the various JavaAppPackaging plugin settings)
mainClass in (Compile, run) := Some("payrules.server.PayRuleServerMain")
bashScriptExtraDefines += """addApp "-http.port=:${PORT:-8080}""""
Customise Docker image generation
packageName in Docker := "payment-rules/api"
dockerRepository := Some("eu.gcr.io")
Optimise Docker image
By default the sbt docker plugin uses openjdk:latest as the base image. You can customise this further
dockerBaseImage := "openjdk:jre-alpine"
If you want to move to a lightweight OS like Alpine or BusyBox, add the following plugin to generate Ash compliant scripts.
enablePlugins(AshScriptPlugin)
Meaningful Docker image and build tags
You can use the sbt-git plugin to give meaningful tags to your images
addSbtPlugin("com.typesafe.sbt" % "sbt-git" % "0.9.3")
In part 2 I will cover how to deploy this Docker image to Google Cloud Run.