Optimize Docker image layering #1677
Description
The default layering is not great for Play Framework applications. Here I create a fresh app and print the layers:
sbt new playframework/play-scala-seed.g8// add to build.sbt
enablePlugins(DockerPlugin, LauncherJarPlugin)[play-scala-seed] $ show dockerLayerMappings
[info] * LayeredMapping(Some(2),/Users/dwickern/code/play-scala-seed/target/scala-2.13/play-scala-seed_2.13-1.0-SNAPSHOT-sans-externalized.jar,/opt/docker/lib/com.example.play-scala-seed-1.0-SNAPSHOT-sans-externalized.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.16/scala-library-2.13.16.jar,/opt/docker/lib/org.scala-lang.scala-library-2.13.16.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/playframework/twirl/twirl-api_2.13/2.0.7/twirl-api_2.13-2.0.7.jar,/opt/docker/lib/org.playframework.twirl.twirl-api_2.13-2.0.7.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/playframework/play-server_2.13/3.0.6/play-server_2.13-3.0.6.jar,/opt/docker/lib/org.playframework.play-server_2.13-3.0.6.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/playframework/play-logback_2.13/3.0.6/play-logback_2.13-3.0.6.jar,/opt/docker/lib/org.playframework.play-logback_2.13-3.0.6.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/playframework/play-pekko-http-server_2.13/3.0.6/play-pekko-http-server_2.13-3.0.6.jar,/opt/docker/lib/org.playframework.play-pekko-http-server_2.13-3.0.6.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/playframework/play-filters-helpers_2.13/3.0.6/play-filters-helpers_2.13-3.0.6.jar,/opt/docker/lib/org.playframework.play-filters-helpers_2.13-3.0.6.jar)
...
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/guava/listenablefuture/9999.0-empty-to-avoid-conflict-with-guava/listenablefuture-9999.0-empty-to-avoid-conflict-with-guava.jar,/opt/docker/lib/com.google.guava.listenablefuture-9999.0-empty-to-avoid-conflict-with-guava.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/code/findbugs/jsr305/3.0.2/jsr305-3.0.2.jar,/opt/docker/lib/com.google.code.findbugs.jsr305-3.0.2.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/checkerframework/checker-qual/3.37.0/checker-qual-3.37.0.jar,/opt/docker/lib/org.checkerframework.checker-qual-3.37.0.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/j2objc/j2objc-annotations/2.8/j2objc-annotations-2.8.jar,/opt/docker/lib/com.google.j2objc.j2objc-annotations-2.8.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/apache/pekko/pekko-protobuf-v3_2.13/1.0.3/pekko-protobuf-v3_2.13-1.0.3.jar,/opt/docker/lib/org.apache.pekko.pekko-protobuf-v3_2.13-1.0.3.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/code/play-scala-seed/target/scala-2.13/play-scala-seed_2.13-1.0-SNAPSHOT-web-assets.jar,/opt/docker/lib/com.example.play-scala-seed-1.0-SNAPSHOT-assets.jar)
[info] * LayeredMapping(Some(2),/Users/dwickern/code/play-scala-seed/target/scala-2.13/com.example.play-scala-seed-1.0-SNAPSHOT-launcher.jar,/opt/docker/lib/com.example.play-scala-seed-1.0-SNAPSHOT-launcher.jar)
[info] * LayeredMapping(Some(4),/Users/dwickern/code/play-scala-seed/target/universal/scripts/bin/play-scala-seed,/opt/docker/bin/play-scala-seed)
[info] * LayeredMapping(Some(4),/Users/dwickern/code/play-scala-seed/target/universal/scripts/bin/play-scala-seed.bat,/opt/docker/bin/play-scala-seed.bat)
[info] * LayeredMapping(Some(1),/Users/dwickern/code/play-scala-seed/conf/logback.xml,/opt/docker/conf/logback.xml)
[info] * LayeredMapping(Some(1),/Users/dwickern/code/play-scala-seed/conf/messages,/opt/docker/conf/messages)
[info] * LayeredMapping(Some(1),/Users/dwickern/code/play-scala-seed/conf/application.conf,/opt/docker/conf/application.conf)
[info] * LayeredMapping(Some(1),/Users/dwickern/code/play-scala-seed/conf/routes,/opt/docker/conf/routes)
[info] * LayeredMapping(None,/Users/dwickern/code/play-scala-seed/target/scala-2.13/api,/opt/docker/share/doc/api/)
[info] * LayeredMapping(None,/Users/dwickern/code/play-scala-seed/target/scala-2.13/api/index.html,/opt/docker/share/doc/api//index.html)
[info] * LayeredMapping(None,/Users/dwickern/code/play-scala-seed/target/scala-2.13/api/index.js,/opt/docker/share/doc/api//index.js)
[info] * LayeredMapping(None,/Users/dwickern/code/play-scala-seed/target/scala-2.13/api/lib,/opt/docker/share/doc/api//lib)
[info] * LayeredMapping(None,/Users/dwickern/code/play-scala-seed/target/scala-2.13/api/lib/source-code-pro-v6-latin-regular.ttf,/opt/docker/share/doc/api//lib/source-code-pro-v6-latin-regular.ttf)
[info] * LayeredMapping(None,/Users/dwickern/code/play-scala-seed/target/scala-2.13/api/lib/annotation_comp.svg,/opt/docker/share/doc/api//lib/annotation_comp.svg)
[info] * LayeredMapping(None,/Users/dwickern/code/play-scala-seed/target/scala-2.13/api/lib/abstract_type.svg,/opt/docker/share/doc/api//lib/abstract_type.svg)
...
[info] * LayeredMapping(None,/Users/dwickern/code/play-scala-seed/target/scala-2.13/api/router/Routes.html,/opt/docker/share/doc/api//router/Routes.html)
[info] * LayeredMapping(None,/Users/dwickern/code/play-scala-seed/target/scala-2.13/api/router/index.html,/opt/docker/share/doc/api//router/index.html)
[info] * LayeredMapping(None,/Users/dwickern/code/play-scala-seed/target/scala-2.13/api/router/RoutesPrefix$.html,/opt/docker/share/doc/api//router/RoutesPrefix$.html)
The biggest issue is that application artifacts are put in the same layer as libraryDependencies. The library dependencies are 43MB for this play-scala-seed app and much larger for any real application. Dependencies change less frequently compared to application code so we should be able to cache them across builds.
Current layers
Here's how the layers are currently structured:
Layer 1
- sbt-native-packager's generated
conf/application.iniif usingUniversal / javaOptions - Play Framework's externalized resources (by default, the contents of
conf/)
Layer 2
- the project's transitive
libraryDependencies - sbt-native-packager's launcher jar if using
LauncherJarPlugin - Play Framework's
-assets.jarand-sans-externalized.jarjars
Layer 3
- sbt-native-packager jlink files if using
JlinkPlugin
Layer 4
- the project's transitive artifact jars
- sbt-native-packager's shell scripts
- sbt-native-packager's classpath jar if using
ClasspathJarPlugin
Final layer (layerId = None)
- sbt-native-packager's mappings of
Docker / sourceDirectory - Play Framework's API docs if using
includeDocumentationInBinary := true(default true)
Proposed layers
At minimum we should move the project artifacts out from layer 2.
Config files shouldn't be the bottom layer. They are only a few KB so it doesn't matter to cache them.
Should jlink files be layered below libraryDependencies? I would guess they change less frequently but I don't use jlink 🤷