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