Determining the Maximum CPU Model for Live Migrations in Proxmox Clusters with ProxCLMC

ProxCLMC – What is it?

Live migration is one of the most powerful and frequently used functions in a Proxmox VE Cluster. However, it presupposes a requirement that is often underestimated: consistent CPU compatibility across all nodes. In real-world environments, clusters rarely consist of identical hardware where you could simply use the CPU type host. Nodes are added over time, CPU generations differ, and functional scopes continue to evolve. Although Proxmox VE allows a flexible CPU configuration, determining a safe and optimal CPU baseline for the entire cluster has so far been largely a manual and experience-based task.

ProxCLMC (Prox CPU Live Migration Checker) was developed by our colleague Florian Paul Azim Hoberg (also known as gyptazy) in Rust as an open-source solution under the GPLv3 license to close this gap in a simple, automated, and reproducible way. The tool examines all nodes of a Proxmox VE cluster, subsequently analyzes their CPU capabilities, and calculates the highest possible CPU compatibility level supported by each node. Instead of relying on assumptions, spreadsheets, or trial and error, administrators receive a clear and deterministic result that can be used directly when selecting VM CPU models.

Comparable mechanisms already exist in other virtualization ecosystems. Enterprise platforms often offer integrated tools or automatic assistance to detect compatible CPU baselines and prevent invalid live migration configurations. Proxmox VE currently does not have such an automated detection mechanism, so administrators must manually compare CPU flags or rely on operational experience. ProxCLMC closes this gap by providing a cluster-wide CPU compatibility analysis specifically tailored to Proxmox environments.

How does ProxCLMC work?

ProxCLMC is designed to integrate seamlessly into existing Proxmox VE clusters without requiring additional services, agents, or configuration changes. It is written entirely in Rust (fully open source under GPLv3), compiled as a static binary, and provided as a Debian package via the gyptazy repository to facilitate easy installation. The workflow follows a clear and transparent process that reflects how administrators think about CPU compatibility but automates it reliably and reproducibly.

After starting, the tool parses the local corosync.conf on the node on which it is running. This allows ProxCLMC to automatically detect all members of the cluster without relying on external inventories or manual input. The determined node list thus always corresponds to the actual state of the cluster.

Once all cluster nodes are identified, ProxCLMC establishes an SSH connection to each node. Via this connection, it remotely reads the content of /proc/cpuinfo. This file provides a detailed and authoritative view of the CPU capabilities provided by the host kernel, including the complete set of supported CPU flags.

From the collected data, ProxCLMC extracts the relevant CPU flags and evaluates them based on clearly defined x86-64 CPU baseline definitions. These baselines are directly based on the CPU models supported by Proxmox VE and QEMU, including:

• x86-64-v1
• x86-64-v2-AES
• x86-64-v3
• x86-64-v4

By mapping the CPU flags of each node to these standardized baselines, ProxCLMC can determine which CPU levels are supported per node. The tool then calculates the lowest common CPU type shared by all nodes in the cluster. This resulting baseline represents the maximum CPU compatibility level that can be safely used for virtual machines while still allowing unrestricted live migrations between all nodes. To get a general idea of the output:


test-pmx01 | 10.10.10.21 | x86-64-v3
test-pmx02 | 10.10.10.22 | x86-64-v3
test-pmx03 | 10.10.10.23 | x86-64-v4
Cluster CPU type: x86-64-v3

With this approach, ProxCLMC brings automated CPU compatibility checking to Proxmox VE-based clusters. Comparable concepts are already known from other virtualization platforms, such as VMware EVC, where CPU compatibility is enforced cluster-wide to ensure secure migrations. ProxCLMC transfers this basic idea to Proxmox environments but implements it in a lightweight, transparent, and completely open manner, thus integrating seamlessly into existing operating procedures and workflows.

Installation of ProxCLMC

ProxCLMC was developed with the goal of enabling easy deployment and integrating cleanly into existing Proxmox VE environments. It can be used directly from the source code or installed as a packaged Debian binary, making it suitable for both development and production environments.

The complete source code is publicly available on GitHub and can be accessed at the following address:
https://github.com/gyptazy/ProxCLMC

This enables complete transparency, auditability, and the ability to adapt or build the tool to individual requirements.

Prerequisites and Dependencies

Before installing ProxCLMC, the following prerequisites must be met:

• A Proxmox VE cluster
• SSH authentication between all Proxmox VE nodes
• Network connection between all cluster members

ProxCLMC uses SSH to remotely examine each node and read CPU information. Passwordless SSH authentication is therefore recommended to ensure smooth and automated execution.

Installation via the Debian Repository

The recommended way to install ProxCLMC on Debian-based systems, including Proxmox VE, is via the Debian repository provided by gyptazy. This repository is also used to distribute the ProxLB project and integrates seamlessly into the usual package management workflows.

To add the repository and install ProxCLMC, execute the following commands:

Using the repository ensures that ProxCLMC can be easily installed, updated, and managed together with other system packages.

Installation via a Debian Package

Alternatively, ProxCLMC can also be installed manually via a pre-built Debian package. This is particularly useful for environments without direct repository access or for offline installations.

The package can be downloaded directly from the gyptazy CDN and installed with dpkg:

This method offers the same functionality as installation via the repository, but without automatic updates.

Conclusion

ProxCLMC exemplifies how quickly gaps in the open-source virtualization ecosystem can be closed when real operational requirements are directly addressed. Similar to the ProxLB project (GitHub), which provides advanced scheduling and balancing functions for Proxmox VE-based clusters, ProxCLMC focuses on a very specific but critical area that was previously largely left to manual processes and experience.

By introducing automated CPU compatibility detection, ProxCLMC brings a functionality to Proxmox VE clusters that is commonly expected in enterprise virtualization platforms but has not yet been available in automated form. It shows that open-source solutions are not limited by missing functions but rather offer the freedom to extend and adapt platforms exactly where it is most important.

With ProxCLMC, operators can now automatically determine the most suitable CPU type for virtual machines in a Proxmox VE cluster, ensuring secure live migrations and consistent behavior across all nodes. Together with projects like ProxLB, this underscores the strength of the open-source model: missing enterprise functions can be transparently added, adapted to real requirements, and shared with the community to continuously improve the Proxmox ecosystem. Should you also require further adjustments or developments around or for Proxmox VE, we would be happy to support you in the realization! Do not hesitate to contact us – we would be happy to advise you on your project!

About the author

gyptazy

Senior DevOps Consultant

about the person

In my tech repertoire, FreeBSD and federated services stand not just as a personal preference but as a symbol of a commitment to the ethos of open-source. I am a fervent believer in the symbiotic relationship between developers including DevOps, SysOps and the open source community. As I continue to lead teams in the ever-evolving landscape of technology, their dedication to open-source contributions and advocacy for decentralized and federated services echoes not only in the code they write but in the ethos they instill within the teams.

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