Add docker-images: one Spring Boot 4 service packaged nine ways

Companion code for "Dockerizing Spring Boot 4: Layered Jars, Buildpacks, Distroless and Image Size Benchmarks". Fat jar on JDK and JRE, layered jar on Debian, Alpine and distroless, jlink, the JDK 25 AOT cache, Paketo buildpacks and Jib, each measured for size on disk and pushed, rebuild delta, startup, user and shell. Also PID 1 and signal handling, the jdeps module gap, AOT cache mismatches and buildpacks memory calculation. Transcripts in docs/output/, regenerated by scripts/run-all.sh. Co-Authored-By: Claude Opus 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01C3TETMrqVUWeFkNtz3Jbo3
2026-09-11 17:11:46 +00:00
parent 86246dc860
commit 644da9e65e
52 changed files with 1308 additions and 1 deletions
@@ -0,0 +1,42 @@
+# 1. The variants and how each is built
+
+[Index](../README.md) · Next: [2. Measuring size →](02-measuring-size.md)
+
+All nine start from the same `target/app.jar` (25 MB). The Dockerfiles are in [`docker/`](../docker),
+each with a comment saying what it is for.
+
+## The layered pattern
+
+```dockerfile
+FROM eclipse-temurin:25-jre AS builder
+WORKDIR /builder
+COPY target/app.jar application.jar
+RUN java -Djarmode=tools -jar application.jar extract --layers --destination extracted
+
+FROM gcr.io/distroless/java25-debian13:nonroot
+WORKDIR /application
+COPY --from=builder /builder/extracted/dependencies/ ./
+COPY --from=builder /builder/extracted/spring-boot-loader/ ./
+COPY --from=builder /builder/extracted/snapshot-dependencies/ ./
+COPY --from=builder /builder/extracted/application/ ./
+ENTRYPOINT ["java", "-jar", "application.jar"]
+```
+
+`extract` without `--launcher` writes a thin `application.jar` whose manifest `Class-Path` lists
+`lib/*.jar`, so the runtime stage launches with plain `java -jar` - no `JarLauncher`, no nested-jar
+class loading. `list-layers` on this jar prints `dependencies`, `spring-boot-loader`,
+`snapshot-dependencies`, `application`, in that order: least likely to change first.
+
+The builder stage uses the Temurin JRE, not the JDK: `extract` needs only a JVM. Only the jlink
+variant needs the JDK, for `jdeps` and `jlink`.
+
+## Buildpacks and Jib in a restricted network
+
+The committed output was produced in a sandbox with no route to Docker Hub or Maven Central. The
+flags that made that work are in [`run-all.sh`](../scripts/run-all.sh):
+
+- Buildpacks: `-Pcorporate-proxy,no-maven-central -Dspring-boot.build-image.pullPolicy=IF_NOT_PRESENT`
+  ([chapter 4](04-buildpacks.md))
+- Jib: `-Djib.from.image=docker://eclipse-temurin:25-jre` - take the base image from the local daemon
+
+With ordinary internet access, `mvn spring-boot:build-image` and `mvn jib:dockerBuild` need no flags.