Docker: Difference between revisions

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m (Re ordered stuff, added doc on sysctl flags that may be needed based on comment from IRC. However since I have not been able to validate these flags, I've commented them out for now.)
(→‎Docker as root: Mention security issue)
 
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Alpine makes a great docker container, because it is so small and optimized to be run in RAM.
== Installation ==
It might also might make a good controller for several docker containers with enough RAM.  I haven't tested this yet
Docker's setup is easy to use from command line.  Commands can be run from an interactive shell, or through a configuration file called a "Dockerfile".
docker.com has excellent walk-throughs on how to run, pull, setup a container, commit an image, and create a configuration file.  hub.docker.com is a freemium setup, where the first private repository is free.


== To install from Alpine ==
The {{Pkg|docker}} package is in the ''community'' repository. See [[Repositories]] how to add a repository.
'''apk add docker'''


The Docker package is in the 'Community' repository, so if the '''apk add''' fails with '''unsatisfiable constraints''', you need to edit the '''/etc/apk/repositories''' file to add (or uncomment) a line like:
apk add docker


'''http://dl-6.alpinelinux.org/alpine/edge/community'''
=== Docker as root ===


To start the Docker daemon at boot, run:
To start the Docker daemon at boot, see [[OpenRC]].


'''rc-update add docker boot'''
rc-update add docker default
service docker start


<!--
Connecting to the Docker daemon through its socket requires you to add yourself to the <code>docker</code> group.
you'll need to disable some kernel security flags:
'''
sysctl -w kernel.grsecurity.chroot_caps=0
sysctl -w kernel.grsecurity.chroot_deny_chmod=0
sysctl -w kernel.grsecurity.chroot_deny_chroot=0
sysctl -w kernel.grsecurity.chroot_deny_mknod=0
sysctl -w kernel.grsecurity.chroot_deny_mount=0
'''
-->


then to start the Docker daemon manually, run:
addgroup ${USER} docker


'''service docker start'''
Adding users to this group will, indirectly, grant them the capability to escalate privileges to that of the root user.


=== Docker rootless ===


== Example: How to install docker from Arch ==
Docker rootless allows unprivileged users to run the docker daemon and docker containers in user namespaces. This is not the same as dockremap explained in the section below. With dockremap the daemon still runs as root.


https://wiki.archlinux.org/index.php/Docker
This requires the {{Pkg|docker-rootless-extras}} package (available in ''community'') and enabling <code>cgroups v2</code>:
edit <code>/etc/rc.conf</code> and set <code>rc_cgroup_mode="unified"</code>. Then start the service on boot:


rc-update add cgroups


== '''How to use docker''' ==
Additionally, the <code>/etc/subuid</code> and <code>/etc/subgid</code> files need to be set up as explained in [https://docs.docker.com/engine/security/rootless/ the official documentation].


The best documentation for how to use Docker and create containers is at the main docker site.  Adding anything more to it here would be redundant.
=== Docker Compose ===


'''http://docs.docker.com/'''
{{Pkg|docker-cli-compose}} is in the ''community'' repository starting with Alpine Linux 3.15.


if you create an account at docker.com you can browse through other user's images and learn from the syntax in contributor's dockerfiles.
apk add docker-cli-compose


Official Docker image files are denoted by a blue ribon on the website.
== Isolate containers with a user namespace ==
<pre>
adduser -SDHs /sbin/nologin dockremap
addgroup -S dockremap
echo dockremap:$(cat /etc/passwd|grep dockremap|cut -d: -f3):65536 >> /etc/subuid
echo dockremap:$(cat /etc/passwd|grep dockremap|cut -d: -f4):65536 >> /etc/subgid
</pre>
 
add to <code>/etc/docker/daemon.json</code>
 
<pre>
{ 
        "userns-remap": "dockremap"
}
</pre>
 
''You may also consider these options : ''
        "experimental": false,
        "live-restore": true,
        "ipv6": false,
        "icc": false,
        "no-new-privileges": false'''''
 
You'll find all possible configurations [https://docs.docker.com/engine/reference/commandline/dockerd/#daemon-configuration-file here].
 
== "WARNING: No {swap,memory} limit support" ==
 
You might encounter this message when executing <code>docker info</code>.
To correct this situation, we have to enable the <code>cgroup_enable=memory swapaccount=1</code>
 
=== Grub ===
If you use Grub, add the cgroup condition into <code>/etc/default/grub</code>, then upgrade your grub
 
<pre>GRUB_CMDLINE_LINUX_DEFAULT="... cgroup_enable=memory swapaccount=1"</pre>
 
=== Extlinux ===
With Extlinux, you add the cgroup condition, but inside of <code>/etc/update-extlinux.conf</code>
 
<pre>default_kernel_opts="... cgroup_enable=memory swapaccount=1"</pre>
 
then update the config and reboot
 
<code>update-extlinux</code>
 
== How to use docker ==
 
Check the [https://docs.docker.com/ official documentation] for details on general usage of docker, including creating and management of containers. Repeating these instructions here be redundant.
 
Public images can be browsed at the [https://hub.docker.com/ Docker Hub]. These should also serve as further reference on the Dockerfile format.
 
Official Docker image files are denoted on the website by a special badge.
 
== See also ==
* [https://www.erianna.com/creating-a-alpine-linux-repository/ Creating and Hosting an Alpine Linux Package Repository for Docker Packages]
* [[Running Alpine in a Docker Container]]
* [https://wiki.archlinux.org/index.php/Docker Docker - ArchWiki]
 
[[Category:Virtualization]]

Latest revision as of 09:27, 2 December 2024

Installation

The docker package is in the community repository. See Repositories how to add a repository. 

apk add docker

Docker as root

To start the Docker daemon at boot, see OpenRC. 

rc-update add docker default
service docker start

Connecting to the Docker daemon through its socket requires you to add yourself to the docker group. 

addgroup ${USER} docker

Adding users to this group will, indirectly, grant them the capability to escalate privileges to that of the root user.

Docker rootless

Docker rootless allows unprivileged users to run the docker daemon and docker containers in user namespaces. This is not the same as dockremap explained in the section below. With dockremap the daemon still runs as root.

This requires the docker-rootless-extras package (available in community) and enabling cgroups v2: edit /etc/rc.conf and set rc_cgroup_mode="unified". Then start the service on boot: 

rc-update add cgroups

Additionally, the /etc/subuid and /etc/subgid files need to be set up as explained in the official documentation.

Docker Compose

docker-cli-compose is in the community repository starting with Alpine Linux 3.15. 

apk add docker-cli-compose

Isolate containers with a user namespace

adduser -SDHs /sbin/nologin dockremap
addgroup -S dockremap
echo dockremap:$(cat /etc/passwd|grep dockremap|cut -d: -f3):65536 >> /etc/subuid
echo dockremap:$(cat /etc/passwd|grep dockremap|cut -d: -f4):65536 >> /etc/subgid

add to /etc/docker/daemon.json 

{  
        "userns-remap": "dockremap"
}

You may also consider these options : 

       "experimental": false,
       "live-restore": true,
       "ipv6": false,
       "icc": false,
       "no-new-privileges": false

You'll find all possible configurations here.

"WARNING: No {swap,memory} limit support"

You might encounter this message when executing docker info. To correct this situation, we have to enable the cgroup_enable=memory swapaccount=1

Grub

If you use Grub, add the cgroup condition into /etc/default/grub, then upgrade your grub 

GRUB_CMDLINE_LINUX_DEFAULT="... cgroup_enable=memory swapaccount=1"

Extlinux

With Extlinux, you add the cgroup condition, but inside of /etc/update-extlinux.conf 

default_kernel_opts="... cgroup_enable=memory swapaccount=1"

then update the config and reboot

update-extlinux

How to use docker

Check the official documentation for details on general usage of docker, including creating and management of containers. Repeating these instructions here be redundant.

Public images can be browsed at the Docker Hub. These should also serve as further reference on the Dockerfile format.

Official Docker image files are denoted on the website by a special badge.

See also

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