KVM Live Migration with Ceph: Enabling Zero-Downtime Base Machine Maintenance

[Praveenkakkera]

Introduction

In a recent customer environment, we successfully implemented and validated zero-downtime live migration of running KVM virtual machines between KVM hosts, using Ceph as the shared storage backend.

The solution uses KVM, QEMU, libvirt, and Ceph without relying on OpenStack or VMware.

The primary objective was to enable maintenance of the underlying KVM base machines without taking critical virtual machines offline.

The Challenge

Critical workloads were running on KVM hosts that periodically require OS patching, kernel upgrades, security updates, hardware maintenance, firmware updates, and reboots.

The key challenge was simple:

How can we perform maintenance on the KVM base machine without impacting the critical workloads running on it?

The Solution

We implemented live migration using:

KVM + QEMU + libvirt + Ceph

The VM disks are hosted on Ceph RBD, providing shared storage accessible by the KVM hosts.

Using live migration, a running VM can be moved from one KVM host to another while continuing to serve its workload.

Zero-Downtime Live Migration

We successfully migrated running critical VMs between KVM hosts with zero service downtime.

The VM remained available during the migration and continued using its Ceph-backed storage after moving to the destination KVM host.

This validated live migration as a practical solution for maintaining workload availability during infrastructure maintenance.

Base Machine Maintenance

The major benefit is the ability to perform maintenance on the underlying KVM host without taking the VM offline.

The process is straightforward:

1. Identify the KVM host requiring maintenance.
2. Validate the destination KVM host and Ceph health.
3. Live migrate the required VMs.
4. Validate VM and application availability.
5. Perform maintenance on the source KVM host.
6. Return the workloads if required.

This enables activities such as OS patching, kernel upgrades, security updates, hardware maintenance, firmware updates, and reboots without impacting critical workloads.

Why Ceph?

Ceph RBD provides shared storage for the VM disks, allowing multiple KVM hosts to access the same VM storage.

This separates VM storage from the physical compute host and enables efficient live migration between KVM hosts.

Conclusion

The successful implementation of zero-downtime KVM live migration with Ceph provides a valuable capability for managing critical workloads.

Using KVM, QEMU, libvirt, and Ceph, we can migrate running VMs between KVM hosts without service downtime and perform planned maintenance on the underlying base machines.

The solution demonstrates that workload mobility and non-disruptive infrastructure maintenance can be achieved without OpenStack or VMware.

Move the workload first. Maintain the base machine second. Keep the service running.