What is the difference between save and export in Docker?

I am playing around with Docker for a couple of days and I already made some images (which was really fun!). Now I want to persist my work and came to the save and export commands, but I don't fully understand them.

What is the difference between save and export in Docker?

Answers


The short answer is:

  • save will fetch an image : for a VM or a physical server, that would be the installation .ISO image or disk. The base operating system.

    It will pack the layers and metadata of all the chain required to build the image. You can then load this "saved" images chain into another docker instance and create containers from these images.

  • export will fetch the whole container : like a snapshot of a regular VM. Saves the OS of course, but also any change you made, any data file written during the container life. This one is more like a traditional backup.

    It will give you a flat .tar archive containing the filesystem of your container.

Edit: as my explanation may still lead to confusion, I think that it is important to understand that one of these commands works with containers, while the other works with images.

  • An image has to be considered as 'dead' or immutable, starting 0 or 1000 containers from it won't alter a single byte. That's why I made a comparison with a system install ISO earlier. It's maybe even closer to a live-CD.

  • A container "boots" the image and adds an additional layer on top of it. This layer stores any change on the container (created/changed/removed files...).


There are two main differences between save and export commands.

  1. save command saves whole image with history and metadata but export command exports only files structure (without history and metadata). So the exported tar file will be smaller then the saved one.

  2. When you use exported file system for creating a new image then this new image will not contain any USER, EXPOSE, RUN etc. commands from your Dockerfile. Only file structure will be transferred. So when you are using mentioned keywords in your Dockerfile then you cannot use export command for transferring image to another machine - you need always use save command.


The exported image will not have any layer or history information saved, so it will be smaller and you will not be able to rollback.

The saved image will have layer and history information, so larger.

If giving this to a customer, the Q is do you want to keep those layers or not?


Technically, save/load works with repositories which can be one or more of images, also referred to as layers. An image is a single layer within a repo. Finally, a container is an instantiated image (running or not).


Docker save Produces a tar file repo which contains all parent layers, and all tags + versions, or specified repo:tag, for each argument provided from image.

Docker export Produces specified file(can be tar or tgz) with flat contents without contents of specified volumes from Container.

docker save need to use on docker image while docker export need to use on container(just like running image)

Save Usage

docker save [OPTIONS] IMAGE [IMAGE...]

Save an image(s) to a tar archive (streamed to STDOUT by default)

--help=false Print usage -o, --output="" Write to a file, instead of STDOUT

export Usage

docker export [OPTIONS] CONTAINER

Export the contents of a container's filesystem as a tar archive

--help=false Print usage -o, --output="" Write to a file, instead of STDOUT


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