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Java - Dockerized spring boot unable to access jarfile?

How to Java - Dockerized spring boot unable to access jarfile

I have a spring boot 3 application that I am trying to deploy on a docker container on an M1 macbook. I am getting error when trying to run the container:

docker run -p 8080:8080 myapp_backend:0.0.1
Error: Unable to access jarfile /app.jar

Dockerfile:

FROM maven:3.8.4-openjdk-17 AS build-stage
WORKDIR /app
COPY pom.xml .
RUN mvn dependency:go-offline

COPY ./src ./src
RUN mvn clean install -Dmaven.test.skip=true

# Stage 2
FROM openjdk:17-jdk-slim AS production-stage
WORKDIR /app
COPY --from=build-stage /app/target/*.jar app.jar

EXPOSE 8080

ENTRYPOINT ["java", "-jar", "/app.jar"]

Docker build logs:

> docker build -t myapp_backend:0.0.1 .      
[+] Building 3.2s (15/15) FINISHED                                                                                                                   docker:rancher-desktop
 => [internal] load build definition from Dockerfile                                                                                                                   0.0s
 => => transferring dockerfile: 735B                                                                                                                                   0.0s
 => [internal] load .dockerignore                                                                                                                                      0.0s
 => => transferring context: 2B                                                                                                                                        0.0s
 => [internal] load metadata for docker.io/library/openjdk:17-jdk-slim                                                                                                 3.2s
 => [internal] load metadata for docker.io/library/maven:3.8.4-openjdk-17                                                                                              3.2s
 => [build-stage 1/6] FROM docker.io/library/maven:3.8.4-openjdk-17@sha256:7106ce47b5c226ee21bac386cb706ff9f3db7ac2f15e251e3aa491fcbfc30028                            0.0s
 => [production-stage 1/3] FROM docker.io/library/openjdk:17-jdk-slim@sha256:aaa3b3cb27e3e520b8f116863d0580c438ed55ecfa0bc126b41f68c3f62f9774                          0.0s
 => [internal] load build context                                                                                                                                      0.0s
 => => transferring context: 1.64kB                                                                                                                                    0.0s
 => CACHED [production-stage 2/3] WORKDIR /app                                                                                                                         0.0s
 => CACHED [build-stage 2/6] WORKDIR /app                                                                                                                              0.0s
 => CACHED [build-stage 3/6] COPY pom.xml .                                                                                                                            0.0s
 => CACHED [build-stage 4/6] RUN mvn dependency:go-offline                                                                                                             0.0s
 => CACHED [build-stage 5/6] COPY ./src ./src                                                                                                                          0.0s
 => CACHED [build-stage 6/6] RUN mvn clean install -Dmaven.test.skip=true                                                                                              0.0s
 => CACHED [production-stage 3/3] COPY --from=build-stage /app/target/*.jar app.jar                                                                                    0.0s
 => exporting to image                                                                                                                                                 0.0s
 => => exporting layers                                                                                                                                                0.0s
 => => writing image sha256:f5ca156d9ebda2118100dc1d75ec6240f3e9c283686ea51599cad313bf5744c8                                                                           0.0s
 => => naming to docker.io/library/myapp_backend:0.0.1                                                                                                           0.0s

Solution:

Based on this:

WORKDIR /app
COPY --from=build-stage /app/target/*.jar app.jar

your app.jar goes to /app/app.jar, not /app.jar. The current directory in docker image build is always the latest WORKDIR.

Yet in your entrypoint you have this:

ENTRYPOINT ["java", "-jar", "/app.jar"]

where you try to run the app.jar from the root (/) directory.

You have two good options. Either

Copy the app.jar to the correct place under root: COPY --from=build-stage /app/target/*.jar /app.jar

Run the app.jar from the correct place under /app/app.jar: ENTRYPOINT ["java", "-jar", "/app/app.jar"]