Run entire docker container with volumes mounted in memory

Question

I would like to run entire docker container in memory without mapping volumes to host's hard drive.

TMPFS described here helps to mount volumes as "memory volumes", but I'm looking a way how to start entire container mapped to memory.

--volume-driver probably what I have to use, but I can't find a documented list of supported drivers (not overlay2).

So, I've tried:

docker run -td --name my-container --volume-driver tmpfs container-image
docker run -td --name my-container --volume-driver memfs container-image

But in both cases, with docker inspect my-container I observed that:

    "GraphDriver": {
        "Data": {
            "LowerDir": "/var/lib/docker/overlay2/d1d112972c6b531976dd33e27edf213fc578856c3ee96b99c9afe53ad3f71a5e- ... /diff",
            "MergedDir": "/var/lib/docker/overlay2/d1d112972c6b531976dd33e27edf213fc578856c3ee96b99c9afe53ad3f71a5e/merged",
            "UpperDir": "/var/lib/docker/overlay2/d1d112972c6b531976dd33e27edf213fc578856c3ee96b99c9afe53ad3f71a5e/diff",
            "WorkDir": "/var/lib/docker/overlay2/d1d112972c6b531976dd33e27edf213fc578856c3ee96b99c9afe53ad3f71a5e/work"
        },
        "Name": "overlay2"
    }

docker stats also points me that both cases are using default mapping strategy.

Cornhusking

I've found the documentation of supported storage drivers docs.docker.com/v17.09/engine/userguide/storagedriver, and seems it is not what I have look for. – Cornhusking

Answer 1

There is an issue that as been closed to do just that. Here is a link to the comment https://github.com/moby/moby/issues/10490#issuecomment-311892718.

In essence, it configures docker to save images in RAM. It will do what you want, but you'll lose your images if you shut down.

Now, I am not sure why you would want that, but I will extrapolate on what I think your need might be:

• You want no trace after the run of your container: Then, add the --rm flag that will remove the files that will always be created. This keeps your run clean, but possibly not completely secure.

• You do not want any of the data you will have to write to be persisted on disk for security reasons : Then you will have to mount a tmpfs (https://docs.docker.com/engine/reference/run/#tmpfs-mount-tmpfs-filesystems) somewhere in your container and only write there. Please keep in mind that if swap is used, the content will be written to disk, and potentially recoverable.

• You want fast read of the data already present in the container: Then I think your best bet is that when your container start, to copy the data you need fast access to in a tmpfs mounted in the container.

I hope I caught your use case and helped, if not, please say so :)

Mesdames

Thanks for your reply! The my main idea to have entire container in memory related to make my tests with database container more stable and quicker. I would like to have all of my tables like memory tables without changing it in table engines and just switch "ground" layer of my database container. – Cornhusking

So, described ideas are really good, and definitely should be applied to different scenarios, you described. But in my case I'm looking to running entire "service" as service in memory only. – Cornhusking

@VictorPerov did you finda solution to this? I have the same use case for our tests. – Arnaud

@digao_mb, maybe open a new question describing your test cases, you'll get more informed answers. – Ruthven

@VictorPerov You can just mount the entire /var/lib/docker to tmpfs, e.g. mount -t tmpfs -o size=1024m tmpfs /var/lib/docker – Indemnification