🛌🏼 👌🏾 👈🏽 Building Optimized Docker Images for a Spring Boot Application 😧 🤵🏽 👩🏻‍🔬

Containers have become the preferred means of packaging an application with all its software and operating system dependencies, and then delivering them to different environments.

This article explores the different ways to containerize your Spring Boot application:

building a Docker image using a Dockerfile,
building an OCI image from source using Cloud-Native Buildpack,
and optimizing the image at runtime by splitting the JARs into different tiers using layered tools.

Sample code

This article is accompanied by a sample working code on GitHub .

Container terminology

We'll start with the container terminology used in the article:

Container image : a file of a specific format. We convert our application to a container image by running the build tool.
Container : An executable instance of a container image.
Container engine : A daemon process responsible for starting a container.
Container host : The host machine that runs the container engine.
(Container registry): , .
OCI: Open Container Initiative (OCI) - , Linux Foundation. OCI , , , .

, . , .

2.3 Spring Boot OCI.

Docker - , Docker , Docker.

Docker Spring Boot , Docker.

JAR , Docker, JAR JRE .

Spring Spring Initializr web, lombok actuator. rest , API GET.

Docker

, Dockerfile:

FROM adoptopenjdk:11-jre-hotspot
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} application.jar
EXPOSE 8080
ENTRYPOINT ["java","-jar","/application.jar"]

Docker , adoptopenjdk, JAR, , 8080 .

Maven Gradle. Maven:

mvn clean package

JAR- . JAR Docker Docker.

JAR Docker, docker build , Docker, :

docker build  -t usersignup:v1 .

docker images

usersignup , adoptopenjdk, Docker.

REPOSITORY          TAG                 SIZE
usersignup          v1                  249MB
adoptopenjdk        11-jre-hotspot      229MB

. dive, :

dive usersignup:v1

Dive:

, . .

Buildpack

(Buildpacks) - , « » (PAAS) . Heroku 2011 Cloud Foundry, Google App Engine, Gitlab, Knative .

Buildpack , (builder) , builder.

. Cloud-Native Buildpacks , OCI, , Docker.

Spring Boot

Spring Boot OCI Buildpack. bootBuildImage (Gradle) spring-boot:build-image (Maven) Docker.

, Docker, image tag:

<plugin>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-maven-plugin</artifactId>
  <configuration>
    <image>
      <name>docker.io/pratikdas/${project.artifactId}:v1</name>
    </image>
  </configuration>
</plugin>

Maven build-image . Docker.

mvn spring-boot:build-image

[INFO] --- spring-boot-maven-plugin:2.3.3.RELEASE:build-image (default-cli) @ usersignup ---
[INFO] Building image 'docker.io/pratikdas/usersignup:v1'
[INFO] 
[INFO]  > Pulling builder image 'gcr.io/paketo-buildpacks/builder:base-platform-api-0.3' 0%
.
.
.. [creator]     Adding label 'org.springframework.boot.version'
.. [creator]     *** Images (c311fe74ec73):
.. [creator]           docker.io/pratikdas/usersignup:v1
[INFO] 
[INFO] Successfully built image 'docker.io/pratikdas/usersignup:v1'

, paketo Cloud-Native buildpack OCI. , , Docker, :

docker images

REPOSITORY                             SIZE
paketobuildpacks/run                  84.3MB
gcr.io/paketo-buildpacks/builder      652MB
pratikdas/usersignup                  257MB

Jib

Jib - Google, .

jib-maven-plugin pom.xml:

      <plugin>
        <groupId>com.google.cloud.tools</groupId>
        <artifactId>jib-maven-plugin</artifactId>
        <version>2.5.2</version>
      </plugin>

Jib Maven, . , Docker:

mvn compile jib:build -Dimage=<docker registry name>/usersignup:v1

Maven :

[INFO] Containerizing application to pratikdas/usersignup:v1...
.
.
[INFO] Container entrypoint set to [java, -cp, /app/resources:/app/classes:/app/libs/*, io.pratik.users.UsersignupApplication]
[INFO] 
[INFO] Built and pushed image as pratikdas/usersignup:v1
[INFO] Executing tasks:
[INFO] [==============================] 100.0% complete

, .

: , . . CI.
: .

Docker , Dockerfile. . Docker , .

Spring Boot « JAR» . JAR, , JAR. , . Spring Framework.

Spring Framework.

, JAR-, -.

, :

, Spring Boot.

Spring Boot Buildpack

Spring Boot 2.3 JAR- . , Spring Boot Maven:

<plugin>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-maven-plugin</artifactId>
  <configuration>
    <layers>
      <enabled>true</enabled>
    </layers>
  </configuration> 
</plugin>

Buildpack, Docker .

build-image Maven :

mvn spring-boot:build-image

Dive, , , ( ) , JAR:

Spring Boot Docker

Maven Gradle JAR Docker Docker.

Docker, .

JAR Maven :

META-INF/
.
BOOT-INF/lib/
.
BOOT-INF/lib/spring-boot-jarmode-layertools-2.3.3.RELEASE.jar
BOOT-INF/classpath.idx
BOOT-INF/layers.idx

JAR spring-boot-jarmode-layertools layersfle.idx. JAR- , .

JAR, -Djarmode=layertools spring-boot-jarmode-layertoolsJAR :

java -Djarmode=layertools -jar target/usersignup-0.0.1-SNAPSHOT.jar

, :

Usage:
  java -Djarmode=layertools -jar usersignup-0.0.1-SNAPSHOT.jar

Available commands:
  list     List layers from the jar that can be extracted
  extract  Extracts layers from the jar for image creation
  help     Help about any command

list, extract help help . list:

java -Djarmode=layertools -jar target/usersignup-0.0.1-SNAPSHOT.jar list

dependencies
spring-boot-loader
snapshot-dependencies
application

, .


`dependencies`	, SNAPSHOT
`spring-boot-loader`	JAR
`snapshot-dependencies`	, SNAPSHOT
`application`

layers.idx , Docker. , . , - .

,

, , . , .

Docker :

# the first stage of our build will extract the layers
FROM adoptopenjdk:14-jre-hotspot as builder
WORKDIR application
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} application.jar
RUN java -Djarmode=layertools -jar application.jar extract

# the second stage of our build will copy the extracted layers
FROM adoptopenjdk:14-jre-hotspot
WORKDIR application
COPY --from=builder application/dependencies/ ./
COPY --from=builder application/spring-boot-loader/ ./
COPY --from=builder application/snapshot-dependencies/ ./
COPY --from=builder application/application/ ./
ENTRYPOINT ["java", "org.springframework.boot.loader.JarLauncher"]

- Dockerfile2.

Docker :

docker build -f Dockerfile2 -t usersignup:v1 .

Sending build context to Docker daemon  20.41MB
Step 1/12 : FROM adoptopenjdk:14-jre-hotspot as builder
14-jre-hotspot: Pulling from library/adoptopenjdk
.
.
Successfully built a9ebf6970841
Successfully tagged userssignup:v1

, Docker , .

, Dive, , Docker. Dive:

dive userssignup:v1

, , , 11 , .

, , , yml layers.idx:

- "dependencies":
  - "BOOT-INF/lib/"
- "spring-boot-loader":
  - "org/"
- "snapshot-dependencies":
- "custom-dependencies":
  - "io/myorg/"
- "application":
  - "BOOT-INF/classes/"
  - "BOOT-INF/classpath.idx"
  - "BOOT-INF/layers.idx"
  - "META-INF/"

layers.idx , io.myorg , .

Cloud-Native Buildpacks . Docker : JAR, , Docker.

, , , , .

, Github .

, .

docker system prune -a

Docker:

docker build -f <Docker file name> -t <tag> .

( Dockerfile):

mvn spring-boot:build-image

. JAR- , spring-boot-maven-plugin:

java -Djarmode=layertools -jar application.jar list