A cluster is a set of servers located at a single location. Distinctive features of such servers (cluster nodes) are their location and high speed of data transfer between them. This article describes the requirements to cluster nodes.

To ensure the stable operation of VMmanager, we do not recommend using a server with a platform as a cluster node.

Nodes homogeneity


We recommend using nodes in one cluster that are homogeneous in terms of network settings, routing, and software versions. This will provide the best conditions for virtual machine migration between cluster nodes.

The platform does not support clusters with both Red Hat (CentOS, AlmaLinux) and Debian based OS nodes.

Virtualization support 


A KVM cluster node must support CPU-level virtualization. To check whether support of Intel and AMD CPUs is available, enter the command:

grep -P 'vmx|svm' /proc/cpuinfo
BASH

If the reply is not an empty string, the CPU supports virtualization.

To use virtualization, make sure it is enabled in the server BIOS.

Hardware requirements


A physical server with the following characteristics can be used as a cluster node:


MinimumRecommended
CPU

2.4 GHz

3 GHz

Core number

4 pcs.

8 pcs.

RAM

8 Gb

16 Gb

Disk space

1 Tb

2 Tb

Motherboard

We recommend using a server motherboard. A cluster node with a desktop motherboard may not work properly.

If you have problems with disk subsystem performance it is recommended to enable the power consumption mode with maximum performance in the BIOS settings.

CPU

Processors with x86_64 architecture are supported.

Disk and storages

When partitioning the disk, we recommend allocating the main volume to the root directory.

Before adding a node to an existing cluster, configure all storage used in the cluster on the server. LXD clusters require configuring a ZFS storage. Read more in LXD.

Software requirements


Operating system

The operating system (OS) requirements depend on the type of virtualization and cluster network configurations:


KVMLXD

Switching

AlmaLinux 8, CentOS 7 x64

Ubuntu 20.04

Routing

AlmaLinux 8, CentOS 7 x64

-

IP fabric

AlmaLinux 8

Ubuntu 20.04

Minor versions of the OS and OS kernel versions may be different between the cluster nodes.

Always use a "clean" OS in its minimum version: without third-party repositories or pre-installed additional services.

Since January 2022, support for CentOS 8 has ended. Running a cluster node on a CentOS 8 server is not supported. You can migrate to AlmaLinux 8 OS according to the instructions.

Software

For the cluster node to work correctly, do not change the default command prompt greeting in the .bashrc file.

In order for the platform to connect to the cluster node, the dmidecode and python3 software packages must be installed on the node. If this software is not included in the OS, install it manually.

OS update

After updating the OS on the cluster node, restart the libvirt service:

systemctl restart libvirtd
BASH

For servers in OVH data center

When installing the OS through the OVH control panel, enable the Install original kernel option. Use the original OS kernel for the cluster servers to work correctly.

Network settings


The network configuration of the cluster nodes must meet the following requirements:

  • each server must have a unique hostname;
  • in clusters with "Switching" and "Routing" configuration type, the server must have access to the Internet;
  • the IP address must be on the physical interface of the server or in the VLAN and be static;
  • the IP address must be static and set via the network interface configuration file (without using DHCP);

  • the default gateway should be available for verification by ping utility.

See the requirements to cluster nodes with two network interfaces in Main and additional network.

If the server is located in a Hetzner data center, we do not recommend using the vSwitch feature. This feature limits the total number of MAC addresses used by physical and virtual server interfaces to 32.

The MTU settings are made at the operating system (OS) level of the cluster node. The platform supports jumbo frames (frames with MTU over 1500 bytes).

KVM virtualization

Allow incoming connections to the ports:

  • 22/tcp — SSH service;
  • 179/tcp, 4789/udp — Virtual networks (VxLAN);
  • 5900-6900/tcp — QEMU VNC, SPICE. If access is only provided through the server with VMmanager, the port range must be open to the network connecting the cluster nodes;
  • 16514/tcp — libvirt virtual machines management service;
  • 49152-49261/tcp — libvirt migration services.

LXD virtualization

Allow incoming connections to the ports:

  • 22/tcp — SSH service;
  • 179/tcp, 4789/udp — Virtual networks (VxLAN);
  • 8443/tcp — LXD container management service.