nmo.md

// LeaseSpec: https://github.com/kubernetes/api/blob/master/coordination/v1/types.go#L40

leasePadding = 30 seconds

Unless otherwise specified, when updating the following fields, always set:

• LeaseDurationSeconds = lifecycle.metal3.io/maintenance + leasePadding,
• AcquireTime = now,
• RenewTime = now,
• HolderIdentity = machine-remediation

A valid lease means: now < LeaseDurationSeconds + AcquireTime

Controller, if lifecycle.metal3.io/maintenance exists:

• if valid lease AND not the current owner:
  • update lifecycle.metal3.io/maintenance-status = waiting
  • exit
• if no lease:
  • create with HolderIdentity, LeaseTransitions = 1, AcquireTime, LeaseDurationSeconds
  • Set ownerRef to refer to the Node
  • update lifecycle.metal3.io/maintenance-status = new, create
• if HolderIdentity doesn’t match:
  • update HolderIdentity, LeaseTransitions + 1, AcquireTime, LeaseDurationSeconds
  • update lifecycle.metal3.io/maintenance-status = new, acquired
  • Ensure lease ownerRef refers to the Node
• if LeaseDurationSeconds == 0
  • update LeaseTransitions + 1, AcquireTime, LeaseDurationSeconds
  • update lifecycle.metal3.io/maintenance-status = new
• if LeaseDurationSeconds != lifecycle.metal3.io/maintenance + leasePadding:
  • // lease interval changed
  • update LeaseDurationSeconds, and RenewTime
  • update lifecycle.metal3.io/maintenance-status = updated
• else if now > (LeaseDurationSeconds + AcquireTime):
  • // The lease records a previous maintenance window
  • // Unlikely but could happen if:
  • // 1. we get API errors preventing the annotation from being deleted prior to the lease expiring
  • // 2. we get API errors preventing LeaseDurationSeconds from being unset and someone recreated the annotation after we deleted it
  • // 3. Reconcile() does not get called within leasePadding of the lease expiring
  • // The second is more likely, so treat as a new request
  • update LeaseDurationSeconds, AcquireTime, and RenewTime
  • update lifecycle.metal3.io/maintenance-status = new, stale
• if lifecycle.metal3.io/maintenance-status == ended
  • // Someone re-created the annotation, with the same interval, after we deleted it, but before we unset LeaseDurationSeconds, and before the old lease expired
  • // Unlikely but could happen if we get API errors preventing LeaseDurationSeconds from being unset
  • // Treat as a request for a new lease starting now
  • update LeaseDurationSeconds, AcquireTime, and RenewTime
  • update lifecycle.metal3.io/maintenance-status = new, recreate
• if (now + leasePadding) > (LeaseDurationSeconds + AcquireTime):
  • delete annotation
  • update lifecycle.metal3.io/maintenance-status = ended
  • if lease time remaining > 0, use a retry loop to uncordon for up to “lease time remaining” seconds
  • if lease time remaining still > 0, use a retry loop to cancel drain for up to “lease time remaining” seconds
  • if lease time remaining still > 0, use a retry loop to set LeaseDurationSeconds = 0 for up to “lease time remaining”
  • exit
• cordon
• drain
• update lifecycle.metal3.io/maintenance-status = active

Controller, if lifecycle.metal3.io/maintenance does not exist:

• if valid lease AND we are the current owner:
  • update lifecycle.metal3.io/maintenance-status = ended
  • if lease time remaining > 0, use a retry loop to uncordon for up to “lease time remaining” seconds
  • if lease time remaining still > 0, use a retry loop to cancel drain for up to “lease time remaining” seconds
  • if lease time remaining still > 0, use a retry loop to set LeaseDurationSeconds = 0 for up to “lease time remaining” seconds
  • on any errors: requeue
• else if LeaseDurationSeconds > 0 and we are the current owner:
  • // We lost the lease prior to tearing down maintenance mode, probably due to API errors
  • // This could result in manual drains/cordons being undone and may not be a good idea to implement
  • // On the other hand, the node will be useless if it remains cordoned
  • update LeaseDurationSeconds = leasePadding, and RenewTime = now
  • if lease time remaining > 0, use a retry loop to uncordon for up to “lease time remaining” seconds
  • if lease time remaining still > 0, use a retry loop to set LeaseDurationSeconds = 0 for up to “lease time remaining” seconds
  • on any errors: requeue

if HolderIdentity doesn’t match:
question: is that equivalent to "if lease expired AND not the current owner: " ?

effectively. why? are you thinking it duplicates "if valid lease AND not the current owner:" ?

Ok, in this case (if HolderIdentity doesn’t match: ) applies to both the case the the lease has expired and that it has not expired. If the lease has not expired and HolderIdentity doesn't match then how is it possible for us to take ownership of the lease just like that? Don't we have to wait for the lease to expire first? (that's my main problem)

f think you will never get to one of the checks:
if lifecycle.metal3.io/maintenance exists:
...
if lifecycle.metal3.io/maintenance-status == ended
because when you transition to ended state you also delete the lifecycle.metal3.io/maintenance annotation. so it won't get to second nested check on a future reconcile call