Docker

Installation

The Docker package is in the 'Community' repository. See Alpine_Linux_package_management how to add a repository.

apk add docker

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

addgroup username docker

To start the Docker daemon at boot, see Alpine_Linux_Init_System.

rc-update add docker boot
service docker start

Note: On older versions of Alpine Linux with older versions of docker you'll also need to disable some kernel security flags in order to build images:

sysctl -w kernel.grsecurity.chroot_deny_chmod=0
sysctl -w kernel.grsecurity.chroot_deny_mknod=0

For more information, have a look at the corresponding Github issue.

This weakening of security is not necessary to do with Alpine 3.4.x and Docker 1.12 as of August 2016.

Docker Compose

'docker-compose' is in the 'Community' repository starting with Alpine Linux 3.10.

apk add docker-compose

For older releases:

To install docker-compose, first install pip:

apk add py-pip python3-dev libffi-dev openssl-dev gcc libc-dev make
pip3 install docker-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[1].

Example: How to install docker from Arch

https://wiki.archlinux.org/index.php/Docker

"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

Alpine 3.8

It may not have been the case before, but with Alpine 3.8, you must config cgroups properly

Warning: This seems not to work with Alpine 3.9 and Docker 18.06. Follow the instructions for grub or extlinux below instead.

echo "cgroup /sys/fs/cgroup cgroup defaults 0 0" >> /etc/fstab

cat >> /etc/cgconfig.conf <<EOF
mount {
cpuacct = /cgroup/cpuacct;
memory = /cgroup/memory;
devices = /cgroup/devices;
freezer = /cgroup/freezer;
net_cls = /cgroup/net_cls;
blkio = /cgroup/blkio;
cpuset = /cgroup/cpuset;
cpu = /cgroup/cpu;
}
EOF

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

The best documentation on using Docker and creating containers is at the main docker site. Adding anything to it here would be redundant.

http://docs.docker.com/

If you create an account at docker.com, you can browse through user images and learn from the syntax in contributed dockerfiles.

Official Docker image files are denoted on the website by a blue ribbon.