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But the killer idea, is that you do not need an OS in these Docker containers. You can basically have a statically linked binary, or a rails app, or sshd
by eikenberry 13y ago
But the killer idea, is that you do not need an OS in these
Docker containers. You can basically have a statically
linked binary, or a rails app, or sshd daemon, and that's it.
Is there documentation of this somewhere? I thought docker relied on having an operating system installed, even if just a minimal busybox based system.
- WestCoastJustin 13y agoI'm not sure if there is documentation at this time, but there was a Google Hangout, entitled "Docker: the Linux container runtime" [1] (minute 24), where Solomon Hykes and Jérôme Petazzoni (from dotCloud, makers of Docker) talk about this very thing. [1] https://www.youtube.com/watch?feature=player_detailpage&v=LDhrDpz8JQw&t=1436 https://www.youtube.com/watch?feature=player_detailpage&v=LD...
- andrewflnr 13y agoA docker container runs in an operating system, but doesn't contain one.
- FooBarWidget 13y agoWell, that depends on your definition of "operating system". Is an OS just the kernel? Then yes, Docker doesn't contain an OS. Is the OS the userland? E.g. the init process + the shell + the C library + other runtimes? Then most Docker containers actually do contain an OS. Yes you can get rid of most of them by making static binaries, but why would you want to? Making static binaries with anything besides Go is a pain, and good luck trying to statically link MySQL or Redis into your binary.
- icebraining 13y agoI don't think you need the init process even without a statically linked binary, and I don't see why would having a bunch of libraries suddenly make it an OS. The linking happens "outside" the container - in the shared kernel.
- justincormack 13y agoI think docker takes the place of init in the container, so no.
- WestCoastJustin 13y agoYou are totally correct. Lets take sshd for example, you would need to create a skeleton directory structure, /bin, /dev, /lib, etc in your rootfs container, have /bin/bash, a whack of /libs, some /dev devices, and then your sshd application. So an extremely minimalistic rootfs with only the sshd requirements. You could find these my running 'lsof -p `pidof sshd`' , maybe 'ldd /usr/sbin/sshd' (and all their dependencies) too, which quickly snowballs. Hopefully this explains where I was going with that. Also, this is not a simple task to try and strip off these services into self contained entities. There are lots of hidden issues, like how do we handle logging? Should the container have syslog too? So, there is work that needs to happen, I just like the idea of not running a full fledged OS in a container.
- mgurlitz 13y agoThis is solved by the union-based filesystem (AUFS) that Docker uses. You start with one minimal rootfs like you describe, given in the "base" image, then when you install sshd you get copy-on-write semantics. So the sshd container gets its own syslog files separate from any other container. Your original comment talks about how long LXC has existed but AUFS is one key component of Docker that became part of mainline Linux much more recently.
- ash 13y ago> AUFS ... became part of mainline Linux much more recently AUFS is not part of mainline kernel. Many distros include it (Debian, Ubuntu). But some don't (Fedora). http://en.wikipedia.org/wiki/Aufs http://en.wikipedia.org/wiki/Aufs
- voltagex_ 13y agoTaking that idea even further, how cool would it be to have one binary that ran a pre-built docker container?