Detection
migetpacks detects a Scala application when any of the following are present in the project root:
build.sbtbuild.scproject/ directory
Version Detection
Scala Version
Scala version is resolved in the following priority order:
| Source | Example |
|---|
.scala-version | 3.5.2 |
build.sbt (scalaVersion) | scalaVersion := "3.5.2" |
project/build.properties (scala.version) | scala.version=3.5.2 |
| Default | 3.5.2 |
sbt Version
sbt version is detected from:
| Source | Example |
|---|
project/build.properties | sbt.version=1.10.6 |
| Default | 1.10.6 |
sbt 0.13.x is deprecated and will show a warning. sbt versions below 0.13.18 are not supported. sbt 2.x support is experimental.
Java Version
The JDK version used for compilation and runtime is read from:
| Source | Example |
|---|
system.properties | java.runtime.version=21 |
| Default | 21 |
Build Process
migetpacks uses the official sbtscala/scala-sbt Docker image which includes sbt, Scala, and the JDK:
# Build stage
FROM sbtscala/scala-sbt:eclipse-temurin-21.0.6_7_1.11.7_3.5.2 AS builder
WORKDIR /build
# Scala/sbt build environment
ENV JAVA_TOOL_OPTIONS="-Dfile.encoding=UTF-8"
ENV SBT_OPTS="-Xmx2G -XX:MaxMetaspaceSize=512m"
# Layer caching: copy sbt build files first
COPY build.sbt ./
COPY project/ project/
# Download dependencies (cached if build files unchanged)
RUN sbt update || true
# Copy source code
COPY . .
# Build and cleanup
RUN sbt compile assembly \
&& rm -rf src/ project/ build.sbt
# Runtime stage
FROM eclipse-temurin:21-jre
WORKDIR /app
COPY --from=builder --chown=1000:1000 /build /app
Framework Detection
migetpacks detects the application type and adjusts the build accordingly:
| Detection | Build Command | Output |
|---|
Play Framework (PlayScala/PlayJava in build.sbt) | sbt compile stage | target/universal/stage/ |
sbt-native-packager (in project/plugins.sbt) | sbt compile stage | target/universal/stage/ |
| Standard sbt project | sbt compile assembly | target/scala-*/app.jar |
Run Command
The default run command depends on the project type:
| Project Type | Default Command |
|---|
| Standard (assembly) | java -jar target/scala-*/app.jar |
| Play Framework | target/universal/stage/bin/{app-name} |
| sbt-native-packager | target/universal/stage/bin/{app-name} |
RUN_COMMAND or a Procfile:
web: java -jar target/scala-3.5.2/myapp-assembly-1.0.jar
JVM Configuration
The following environment variables are set for production:
| Variable | Value |
|---|
JAVA_OPTS | -Dfile.encoding=UTF-8 -XX:MaxRAMPercentage=80.0 |
JAVA_TOOL_OPTIONS | -Dfile.encoding=UTF-8 |
Caching
Layer Caching
Dependencies are cached by copying sbt build definition files before the full source:
| Cached Files | Purpose |
|---|
build.sbt | Project build definition |
project/ | sbt plugins, build properties, Scala version |
| Scenario | Dependency Install |
|---|
| First build | Runs |
| Source code change only | Cached |
| Build file change | Runs |
BUILD_CACHE_DIR
When BUILD_CACHE_DIR is set, sbt and dependency caches persist at:
| Cache Path | Contents |
|---|
| sbt cache | sbt boot and global settings |
| ivy cache | Ivy repository (legacy dependencies) |
| coursier cache | Coursier downloads (modern dependencies) |
DHI Support
Docker Hardened Images are supported for Scala runtime.
sbtscala build image (which includes sbt tools) for building, and a DHI distroless image for runtime.
| Stage | Image |
|---|
| Build | sbtscala/scala-sbt:eclipse-temurin-{jdk}_{sbt}_{scala} (official) |
| Runtime | dhi.io/eclipse-temurin:{java} |
DHI Notes
- The build image is always the official sbtscala image (DHI does not provide sbt images).
- Only the runtime stage uses DHI distroless Eclipse Temurin JRE.
- Java version is read from
system.properties (default: 21).
- Runtime images are distroless (no shell).
Example with DHI
docker run --rm \
-v /path/to/scala-app:/workspace/source \
-v /var/run/docker.sock:/var/run/docker.sock \
-e OUTPUT_IMAGE=my-scala-app:latest \
-e USE_DHI=true \
miget/migetpacks:latest
Example
docker run --rm \
-v /path/to/scala-app:/workspace/source \
-v /var/run/docker.sock:/var/run/docker.sock \
-e OUTPUT_IMAGE=my-scala-app:latest \
miget/migetpacks:latest
Play Framework app
docker run --rm \
-v /path/to/play-app:/workspace/source \
-v /var/run/docker.sock:/var/run/docker.sock \
-e OUTPUT_IMAGE=my-play-app:latest \
-e RUN_COMMAND="target/universal/stage/bin/myapp -Dhttp.port=5000" \
miget/migetpacks:latest
