The key changes in OpenVZ are:
- OpenVZ becomes a complete Linux distribution based on our own VzLinux.
- The main difference between the Virtuozzo (commercial) and OpenVZ (free) versions are the EULA, packages with paid features, and Anaconda installer.
- EZ templates can be used instead of tarballs with template caches.
- RHEL7 (3.10+) kernel.
- KVM/QEMU hypervisor.
- Guest tools for virtual machines that currently allow the following: to execute commands in VMs from the host, to set user passwords, to set and obtain network settings, to change SIDs, to enter VMs.
- Unified management of containers and KVM virtual machines with the prlctl tool and SDK. You get a single universal toolset for all your CT/VM management needs.
- UUIDs are used to identify both virtual machines and containers. With containers, prlctl treats the former VEID parameter as name.
- Virtual machine HDD images are stored in the QCOW2 format.
- Ability to manage containers and VMs with libvirt and virt-manager or virsh via a single driver for containers and virtual machines. Libvirt is an open-source API, daemon, and management tool for managing virtualization platforms. The API is widely used in the orchestration layer of hypervisors for cloud-based solutions. OpenVZ considers libvirt as the standard API for managing both virtual machines and containers. Libvirt provides storage management on the physical host through storage pools and volumes which can be used in OpenVZ containers.
- Memory guarantees. A memory guarantee is a percentage of container’s or virtual machine’s RAM that said container or VM is guaranteed to have.
- Memory hotplugging for containers and VMs that allows both increasing and reducing CT/VM memory size on the fly, without the need to reboot. Your customers can now scale their workloads without any downtime. This feature also enables you to make PAYG offerings, allowing customers to change VM resources depending on workload and potentially pay less.
- Kernel same-page merging. To optimize memory usage by virtual machines, OpenVZ uses a Linux feature called Kernel Same-Page Merging (KSM). The KSM daemon ksmd periodically scans memory for pages with identical content and merges those into a single page.
- VCMMD, the fourth-generation unified memory manager, and vcmmd, a single daemon for managing memory of both virtual machines and containers. OpenVZ uses memcg. Balancing and configuring memcg limits enables getting the exact OpenVZ parameters like overcommit, shadow gangs, swap, page cache overuse.
- Container live migration via CRIU and P.Haul. In the previous versions of OpenVZ, most operations performed during migration were done in the kernel space. As a result, the migration process imposed a lot of restrictions. To improve upon migration, Virtuozzo launched the CRIU project aiming to move most of the migration code to the user space, make the migration process reliable, and remove excessive restrictions.
- Containers use cgroups and namespaces that limit, account for, and isolate resource usage as isolated namespaces of a collection of processes. The beancounters interface remains in place for backward compatibility and, at the same time, acts as a proxy for actual cgroups and namespaces implementation.
- SimFS remains in OpenVZ, however, the support is limited and we don’t have plans to improve it in future.
