Acquire a scheduler lease atomically under competing instances
Two instances see an expired lease and both believe they became the active scheduler.
- Focused work estimate
- 3h 30m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Transactions · Leader coordination
Estimated field mix
- Distributed systems60%
- Database engineering40%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional document service runs periodic retention planning on multiple application instances. Paused instances resume after lease expiry and can overlap newer schedulers.
Setup prerequisites
- Create a synthetic maintenance queue and two independent scheduler clients.
- Use fake time where possible and no destructive real retention actions.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Acquire through one guarded database transaction.
- Increment the epoch only for the winning acquisition.
- Return current safe ownership metadata to the loser.
Implementation constraints
- Use two independent database connections and a barrier.
Verification to include
- Race two acquisitions and assert one winning epoch.
- Hold a valid lease and verify another instance cannot replace it early.
Deliverables
- Atomic acquisition command and race test
Rollout and recovery
Canary with two local clients; stop scheduling if ownership results conflict.
Value of the work
For the engineer: Practice lease assumptions, fencing and stale-owner rejection.
For the team: Review safe coordination that remains explainable under pauses and recovery.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.