This article describes the migration of OpenVZ containers to Linux containers (LXC). OpenVZ is not available for Kernels above 2.6.32, therefore a migration is necessary. Linux Container technology is available in all mainline Linux kernels and a future proof technology introduced in Proxmox VE 4.x series.

Basically you have to follow these steps:

On the Proxmox VE 3.x node (We recommend to a fresh installation of Proxmox VE 4):

1. note the network settings used by the container
2. make a backup of the OpenVZ container

On the Proxmox VE 4.x node:

1. create a LXC container based on the backup
2. configure the network with the previous settings
3. boot and voilà, it works

Note that all the steps mentioned here can be done with the Web GUI. However, it is easier to split the steps in command line actions. This allows to script the steps if there is a bigger number of containers to convert.

https://pve.proxmox.com/wiki/Convert_OpenVZ_to_LXC

https://pve.proxmox.com/wiki/Convert_OpenVZ_to_LXC