To shrink the docker image

The best way to create a small Docker image is to rebuild a small base image, such as Alpine Linux or BusyBox, with minimal changes.
But this is probably not something I want to do, so I'll give you another way.

The reason for the large size of the Docker image is the increase in the number of layers.
test/i386-ubuntu:1.1.4 is larger because it is layered from 1.1.1.
Whatever you do on top of this image will not reduce the size.

I think the only way to reduce the size is to create a new image of layers in one layer.
Docker doesn't have the ability to put layers together yet.
Suggested in PR#13929 or PR#4232 but it seems to have been rejected.
PR#22641 is the docker build plus the option --squash and has already been merged and
I think I can use it to organize the layers, but it hasn't been released yet.

Third-party docker-flatten or docker-squash
There is , but it is your responsibility to use it.

Other methods include using docker export and docker import.

docker export<container ID>|docker import-<image name>:<tag>

However, if you do this, the attributes given to the image in dockerbuild (Dockerfile) will disappear.
Examples include VOLUME, EXPOSE, and ENV.I think it's good to think that only the file system is retained.

Note that docker export targets containers, not images.
Similar commands for images include docker save/docker load, which cannot be used to reduce the image size because it keeps layers together.

docker export You can create a smaller image by deleting unnecessary files and packages in the container or by deleting the cache with apt-get clean.