Image size difference in multistage builds by kaniko and docker

[jaskeerat789]

Actual behavior
The image size of a multistage image build by docker is very large as compared to docker. Kaniko might not be discarding builder stage image. This is an initial hunch. I am using kaniko with Gitlab CI running on EKS cluster.

Expected behavior
The image size build by kaniko should be similar to that of image built by docker

To Reproduce
Steps to reproduce the behavior:

1. Build the following Dockefile locally
2. Build the same Dockerfile using kaniko
3. compare the size of images pushed to repo

Additional Information

• Dockerfile

FROM <private centos image with java 8> AS builder
WORKDIR /builds

COPY . /builds/
RUN ./gradlew clean build

#################### Runner Image ######################## 
FROM amazoncorretto:8-alpine3.17
WORKDIR /home/app

COPY --from=builder /builds/build/libs/app.jar ./app.jar
COPY ./startApp.sh .

USER app-user
EXPOSE 8080

ENTRYPOINT ["/bin/ash"]
CMD ["startApp.sh"]

• Build Context: Building a java application using gradle in first stage and using jar file built in the second stage
• Kaniko Image: gcr.io/kaniko-project/executor:v1.15.0-debug
• Difference in sizes. First one is built and pushed by kaniko whereas the second image was built and pushed by docker running locally on an intel macbook .

Triage Notes for the Maintainers

Description	Yes/No
Please check if this a new feature you are proposing
Please check if the build works in docker but not in kaniko
Please check if this error is seen when you use --cache flag
Please check if your dockerfile is a multistage dockerfile

[aaron-prindle]

Thank you for flagging this @jaskeerat789. This issue has been reported previously here:
#2261

Feel free to continue the conversation there, going to close this as a dupe