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Docker inside CT

Revision as of 22:40, 11 February 2015 by Kir (talk | contribs) (add prereq)

Since OpenVZ kernel 042stab105.4 it is possible to run Docker inside containers. This article describes how.

Contents

Prerequisites

  • Kernel 042stab105.4 or later version
  • Kernel module veth module is loaded on host

Container tuning

  • 1. Create Fedora 20 container:
vzctl create $veid --ostemplate fedora-20-x86_64
  • 2. Turn on bridge feature to allow docker creating bridged network:
vzctl set $veid --features bridge:on --save
  • 3. Setup Container veth-based network:
vzctl set $veid --netif_add eth0 --save
  • 4. Allow all iptables modules being used in containers:
vzctl set $veid --netfilter full --save
  • 5. Configure custom cgroups in systemd:
vzctl mount $veid
echo "JoinControllers=cpu,cpuacct,cpuset,freezer,devices" >> /vz/root/$veid/etc/systemd/system.conf 
  • 6. Start the container:
vzctl start $veid

Prepare Docker in container

These steps are to be performed inside the container.

  • 1. Install Docker:
yum -y install docker-io
  • 2. Start docker daemon
 docker -d -s vfs

Example usage

Wordpress

Use Docker to start Wordpress (official, standard way).

  • 1. Start mysql docker:
docker run --name test-mysql -e MYSQL_ROOT_PASSWORD=123 -d mysql
  • 2. Start wordpress:
docker run --name test-wordpress --link test-mysql:mysql -p 8080:80 -d wordpress
  • 3. Access wordpress server by container IP and port 8080:
    http://container_ip:8080

Limitations

  • This feature is currently in beta
  • Only "vfs" Docker graph driver is currently supported