How to save a Docker container state

Question

I'm trying to learn the ins and outs of Docker, and I'm confused by the prospect of saving an image.

I ran the basic Ubuntu image, installed Anaconda Python and a few other things...so now what's the best way to save my progress? Save, commit, export?

None of these seem to work the same way as VirtualBox, which presents an obvious save-state file for your virtual machine.

Answer 1

The usual way is at least through a docker commit: that will freeze the state of your container into a new image.

Note: As commented by anchovylegend, this is not the best practice, and using a Dockerfile allows you to formally modeling the image content and ensure you can rebuild/reproduce its initial state.

You can then list that image locally with docker images, and run it again.

Example:

$ docker ps  CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS              NAMES c3f279d17e0a        ubuntu:12.04        /bin/bash           7 days ago          Up 25 hours                            desperate_dubinsky 197387f1b436        ubuntu:12.04        /bin/bash           7 days ago          Up 25 hours                            focused_hamilton  $ docker commit c3f279d17e0a  svendowideit/testimage:version3  f5283438590d  $ docker images  REPOSITORY                        TAG                 ID                  CREATED             SIZE svendowideit/testimage            version3            f5283438590d        16 seconds ago      335.7 MB 

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After that, if you have deployed a registry server, you can push your image to said server.

Answer 2

The usual way is at least through a docker commit: that will freeze the state of your container into a new image.

But know that there is no reliable way to "save state" of container unlike virtual machine save state in Hyper-V or VMware. This is a downside also to docker.

It seems it only saves the changes made to the persistent file changes. So when you spin up the container again from new images, the dependencies and all the run commands executed will not have same effect.

That's why its ideal to have to changes in docker file and in short, there is no save state feature in docker system like we have in virtual machines. The memory contents are always lost.