Lease

You might say

Two scheduler instances must not run the same summary. Let one hold time-limited ownership, let it expire after failure, and let the other take over.

A lease is time-limited ownership that must be renewed and can be taken over after it expiresIf two scheduler instances can run the daily summary, one can acquire and renew a lease while the other waits. If the holder fails, the lease expires and a waiting instance can take over. A lease only decides who may take over: a delayed old holder can still write, so each takeover also needs a larger fencing token that the write target checks atomically to reject stale holders.

How two schedulers avoid running one job at the same time

Billing-job leader leaseDaily at 09:00

instance Aready to bill

instance Balso ready

duplicate riskmay run twice

EvidenceBoth instances observe the same schedule

Without coordination, the job can run twice.

A lease limits ownership by time

Control takeover with renewal and expiry: Without coordination, both schedulers can start the daily summary. A lease lets only the current holder run and renew ownership. If it fails or disconnects, a waiting instance must wait for expiry before acquiring a new lease and taking over.

Verify the old-holder risk: Each successful takeover receives a larger fencing token, and the database or target service compares it atomically when accepting a write. Pause A through expiry, let B take over, then resume A and verify that A's stale write is rejected.

Another case: controller leadership: When several controllers can update the same resources, a lease can elect the current leader and be renewed. After failure, a new controller takes over with a newer token so the old leader cannot keep submitting changes.

Quick checkChoose the best answer

The current scheduler is unreachable and another instance is ready to run the same job. When may it take over?

Confirm expiry, acquire a larger fencing token, and have the write target atomically reject stale tokensWait forever unless the old instance releases the lease itselfIgnore lease state and start as soon as one heartbeat is late

You can say this to an AI Agent

Use a lease for the daily summary job: an instance acquires time-limited ownership and renews it while running; after expiry, the new holder receives a larger fencing token. Make the database or target service atomically reject writes whose token is older than the current one. Pause instance A until expiry, let B take over and write, then resume A; verify that A's stale write is rejected and only B's result is accepted.

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