I tried to add a file via ADD command and then deleted it. But the size of docker images also shows that it includes that files! If I put * in .dockerignore, it will not work with ADD.

Dockerfile:

from ubuntu:20.04

ADD myfile /tmp

RUN rm /tmp/*

Then I built it by
$ docker build -t testwf .

At the first stage it shows the below:

Sending build context to Docker daemon  34.21MB

The size of myfile file is around 33MB

$ docker images
REPOSITORY                       TAG       IMAGE ID       CREATED          SIZE
testwf                           latest    96543168ab34   16 minutes ago   107MB
ubuntu                           20.04     ba6acccedd29   5 weeks ago      72.8MB

Actually, I was supposed to get an image with 72.8MB the same size with ubuntu not 107MB which is roughly equal to 72.8MB plus 33MB! In other words, If I didn’t have that file with ADD command, was there any way to access the file in the container as it was copied to Docker daemon?

update

As HansKilian mentioned in the comments that file went in one of the layers where the final image is constructed on top of that. Is there any way to get rid of that layer in order to decrease the size of the final image?

$ docker history testwf:latest                                                                  
IMAGE          CREATED         CREATED BY                                      SIZE      COMMENT
2af2733972ab   4 seconds ago   /bin/sh -c rm /tmp/*                            0B
40d13da4e0cc   4 seconds ago   /bin/sh -c #(nop) ADD file:0ddf694d27b108b4a…   34.2MB
ba6acccedd29   5 weeks ago     /bin/sh -c #(nop)  CMD ["bash"]                 0B
<missing>      5 weeks ago     /bin/sh -c #(nop) ADD file:5d68d27cc15a80653…   72.8MB

>Solution :

You can have a multistage build:

FROM alpine:latest  
ADD myfile /tmp

from ubuntu:20.04
COPY --from=0 /tmp/myfile ./
RUN rm /tmp/*