OS subscriptions are recurring per-vCPU or per-socket costs, and the CentOS Stream shift pushed many shops to rebuild their Linux strategy. RHEL-compatible rebuilds (Rocky Linux, AlmaLinux) and Ubuntu/Debian remove or reduce the subscription while keeping workloads largely unchanged.
Two paths: convert or reprovision
- In-place conversion — RHEL→Rocky/Alma is famously low-friction via
migrate2rocky/almalinux-deploy, swapping the distro in place. Fast, but snapshot first. - Reprovision — build a golden image / Ansible roles for the target and redeploy. Cleaner long-term, and the right call when changing distro families (e.g. RHEL→Ubuntu) or modernizing config management.
What to check
Inventory packages, services, and configuration; map application/runtime certifications (some ISV support matrices are distro-specific) and kernel/driver dependencies. Map package equivalents across dnf/apt/zypper, and confirm repo access. Windows→Linux re-platforming is a bigger lift — only supported apps move cleanly.
Sizing & cost
On VMs, RHEL/SUSE/Windows are effectively counted by vCPU (or per-VM subscription); Windows Datacenter licenses host cores but allows unlimited VMs. The open rebuilds are free (support optional via CIQ, Canonical, etc.).
Flow & validation
Snapshot → convert or reprovision → reboot and verify the OS, services, and agents (backup/monitoring/security) → run application smoke and regression tests → re-register configuration management. Run a patch-and-reboot cycle test before declaring success. Rollback = restore the snapshot or redeploy the prior image.
De-risking
Convert a non-production clone first to surface package/driver/boot issues, then roll out in waves. Keep snapshots through hypercare.
Open a source→target page for the exact conversion commands and a per-vCPU TCO model.