One-liner: Upgrades bring benefits and risks — run them in small batches, with tested rollback points and a rehearsal beforehand.
Top risks (quick):
- Compatibility issues (firmware/drivers/plugins)
- Host boot / cluster join failures
- Network / SDN outages causing service inaccessibility
- Storage mount or format incompatibilities
- Automation/monitoring/backup integrations breaking
Must-do before upgrading (minimum):
- Full backups: management plane configs, host images, and certificates.
- Run one upgrade+rollback rehearsal in a test cluster.
- Plan phased upgrades and define clear rollback triggers.
Simple rollback steps:
- Trigger rollback on critical service failures or cluster join errors.
- Stop all remaining upgrades and isolate failed nodes.
- Restore management-plane config in an isolated environment and verify.
- Roll back hosts from pre-upgrade images one-by-one; verify boot and networking.
- Restore critical VMs by priority, run health checks, and monitor for 30–60 minutes.
Tip: Make upgrade scripts idempotent, validate in a small non-production group first, and avoid simultaneous large changes (network/storage) during the upgrade window.
