Docker: Difference between revisions

Latest revision as of 18:52, 14 March 2025

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

Warning: Adding users to this group will is equivalent to granting them full root access on the host. See upstream documentation.

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.

Now docker can be start from an unprivileged user with

 dockerd-rootless

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.

@@ Line 15: / Line 15: @@
   addgroup ${USER} docker
+{{Warning|Adding users to this group will is equivalent to granting them full root access on the host. [https://docs.docker.com/engine/security/security/#docker-daemon-attack-surface See upstream documentation].}}
 === Docker rootless ===
@@ Line 26: / Line 28: @@
 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].
+Now docker can be start from an unprivileged user with
+  dockerd-rootless
 === Docker Compose ===