Comparison
Node drainvsPod disruption budget
Node drain
you mark the machine unschedulable and evict everything on it politely, so the upgrade takes an hour instead of a page.
The two-step process for taking a node out of service: cordon it so nothing new is scheduled there, then evict what is running so it moves elsewhere. It is the routine operation behind every upgrade, resize and spot reclamation, and it is where disruption budgets, grace periods and shutdown handling are all tested at once. A drain that hangs is nearly always a workload with no other place to go or a budget that cannot be met.
Full entry →Pod disruption budget
a node upgrade rolled through the cluster and stopped, because taking one more replica down would have breached what you declared.
A declaration of how much of a workload may be voluntarily unavailable at once, which drains and upgrades must respect. It is the only thing standing between a routine cluster upgrade and every replica of a service being evicted in sequence faster than it can start. It constrains only voluntary disruption — a node catching fire does not consult it — and a budget that can never be satisfied will wedge an upgrade indefinitely.
Full entry →