Difference between revisions of "Docker"

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Alpine makes a great docker container, because it is so small and optimized to be run in RAM.
 
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.
 
 
 
== Installation ==
 
== Installation ==
 
Run <code>apk add docker</code> to install Docker on Alpine Linux.
 
 
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:
 
 
<code>http://dl-cdn.alpinelinux.org/alpine/edge/community</code>
 
 
then run <code>apk update</code> to index the repository.
 
  
 +
The Docker package is in the 'Community' repository. See [[Alpine_Linux_package_management]] how to add a repository.
  
'''To start the Docker daemon at boot, run:'''
+
apk add docker
  
<code>rc-update add docker boot</code>
+
Connecting to the Docker daemon through its socket requires you to add yourself to the `docker` group.
  
 +
addgroup username docker
  
'''Then to start the Docker daemon manually, run:'''
+
To start the Docker daemon at boot, see [[Alpine_Linux_Init_System]].
 
 
<code>service docker start</code>
 
  
 +
rc-update add docker boot
 +
service docker start
  
 
{{Note|On older version of Alpine Linux with older version of docker you'll also need to disable some kernel security flags in order to build images:}}
 
{{Note|On older version of Alpine Linux with older version of docker you'll also need to disable some kernel security flags in order to build images:}}
  
<code>sysctl -w kernel.grsecurity.chroot_deny_chmod=0</code>
+
sysctl -w kernel.grsecurity.chroot_deny_chmod=0
 
+
sysctl -w kernel.grsecurity.chroot_deny_mknod=0
<code>sysctl -w kernel.grsecurity.chroot_deny_mknod=0</code>
 
  
 
For more information, have a look at the [https://github.com/docker/docker/issues/20303 corresponding Github issue].
 
For more information, have a look at the [https://github.com/docker/docker/issues/20303 corresponding Github issue].
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=== Docker Compose ===
 
=== Docker Compose ===
  
'''To install docker-compose, first install pip:'''
+
'docker-compose' is in 'Community' repository since Alpine Linux >= 3.10.
  
<code>apk add py-pip</code>
+
apk add docker-compose
  
 +
For older releases, do:
  
'''Then install docker-compose, run:'''
+
'''To install docker-compose, first install pip:'''
  
<code>pip install docker-compose</code>
+
apk add py-pip python3-dev libffi-dev openssl-dev gcc libc-dev make
 +
pip3 install docker-compose</code>
  
 
== Isolate containers with a user namespace ==
 
== Isolate containers with a user namespace ==
 
<pre>
 
<pre>
 
adduser -SDHs /sbin/nologin dockremap
 
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: -f3):65536 >> /etc/subuid
 
echo dockremap:$(cat /etc/passwd|grep dockremap|cut -d: -f4):65536 >> /etc/subgid
 
echo dockremap:$(cat /etc/passwd|grep dockremap|cut -d: -f4):65536 >> /etc/subgid
 
</pre>
 
</pre>
  
and add in '''/etc/init.d/docker'''
+
and add in '''/etc/docker/daemon.json'''
  
 
<pre>
 
<pre>
DOCKER_OPTS="--userns-remap=default"                  
+
 +
        "userns-remap": "dockremap"
 +
}
 
</pre>
 
</pre>
  
''You may also consider these options : '''--icc=false --no-new-privileges'''''
+
''You may also consider these options : '''
 +
        "experimental": false,
 +
        "live-restore": true,
 +
        "ipv6": false,
 +
        "icc": false,
 +
        "no-new-privileges": false'''''
 +
 
 +
You will find all possible configurations here[https://docs.docker.com/engine/reference/commandline/dockerd/#daemon-configuration-file].
  
 
== Example: How to install docker from Arch ==
 
== Example: How to install docker from Arch ==
  
 
https://wiki.archlinux.org/index.php/Docker
 
https://wiki.archlinux.org/index.php/Docker
 +
 +
== "WARNING: No {swap,memory} limit support" ==
 +
 +
You may, probably, encounter this message by executing <code>docker info</code>.
 +
To correct this situation we have to enable the <code>cgroup_enable=memory swapaccount=1</code>
 +
 +
==== Alpine 3.8 ====
 +
Well I'm not sure it wasn't the case before but for sure 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.
 +
 +
<pre>echo "cgroup /sys/fs/cgroup cgroup defaults 0 0" >> /etc/fstab</pre>
 +
<pre>
 +
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
 +
</pre>
 +
 +
=== Grub ===
 +
Well; if you use Grub it is like any other linux and you just have to add the cgroup condition into <code>/etc/default/grub</code>, then upgrade your grub
 +
 +
<pre>GRUB_CMDLINE_LINUX_DEFAULT="... e=memory swapaccount=1"</pre>
 +
 +
=== Extlinux ===
 +
With Extlinux you also add the cgroup condition but inside <code>/etc/update-extlinux.conf</code>
 +
 +
<pre>default_kernel_opts="... cgroup_enable=memory swapaccount=1"</pre>
 +
 +
than update the config and reboot
 +
 +
<code>update-extlinux</code>
  
 
== '''How to use docker''' ==
 
== '''How to use docker''' ==
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== See also ==
 
== See also ==
 
* [https://www.erianna.com/creating-a-alpine-linux-repository/ Creating & Hosting an Alpine Linux Package Repository for Docker Packages]
 
* [https://www.erianna.com/creating-a-alpine-linux-repository/ Creating & Hosting an Alpine Linux Package Repository for Docker Packages]
 +
* [[Running Alpine in a Docker Container]]
  
 
[[Category:Virtualization]]
 
[[Category:Virtualization]]

Latest revision as of 16:24, 17 September 2020

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 version of Alpine Linux with older version 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.

Anyway, this weakening of security is not necessary to do with Alpine 3.4.x and Docker 1.12 as of August 2016 anymore.

Docker Compose

'docker-compose' is in 'Community' repository since Alpine Linux >= 3.10.

apk add docker-compose

For older releases, do:

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

and add in /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 will 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 may, probably, encounter this message by executing docker info. To correct this situation we have to enable the cgroup_enable=memory swapaccount=1

Alpine 3.8

Well I'm not sure it wasn't the case before but for sure 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

Well; if you use Grub it is like any other linux and you just have to add the cgroup condition into /etc/default/grub, then upgrade your grub

GRUB_CMDLINE_LINUX_DEFAULT="... e=memory swapaccount=1"

Extlinux

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

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

than update the config and reboot

update-extlinux

How to use docker

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.

http://docs.docker.com/

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.

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

See also