Scaling localnet user-defined networks (CUDNs) in Red Hat OpenShift to 3,500 networks

Summary

Migrating from legacy virtualization with flat VLAN-based tenant networks to Red Hat OpenShift Virtualization often requires re-architecting network topology, creating friction. Red Hat OpenShift supports localnet user-defined networks (CUDNs) to preserve existing VLAN infrastructure while modernizing. Red Hat tested localnet CUDNs at scale, successfully managing up to 3,500 localnet CUDNs hosting over 3,500 active virtual machines. OVN-Kubernetes achieved 100% SSH connectivity, near-line-speed data-path performance over 100GbE interfaces without Geneve tunnel overhead, and stable control plane resource usage. Resource peaks reached approximately 5.5 CPU cores per worker node and 10 CPU cores on control plane nodes during bulk creation, then returned to low baselines.

Takeaways

1. 1

   Localnet CUDNs eliminate Geneve tunnel encapsulation and complex routing between nodes, offloading overlay management to the physical network and drastically reducing OVN-Kubernetes overhead.

2. 2

   In testing, 3,500 localnet CUDNs with 3,500 VMs achieved 100% SSH success and near-line-speed data-path throughput over 100GbE interfaces, without tunnel-related CPU overhead.

3. 3

   During mass creation of CUDNs and VMs, OVN-Kubernetes CPU usage peaked at about 5.5 cores per worker node and 10 cores on the control plane, then returned to low idle baselines after creation completed.

FAQ