Make scheduled maintenance occurrences idempotent across leadership changes
A new leader repeats the current maintenance period and creates a second plan for the same logical occurrence.
- Focused work estimate
- 4h + prerequisites
- Priority in the scenario
- Medium
- Engineering practice
- Idempotency · Scheduling
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.
- ALEASE-101 · Specify scheduler lease state with a separate authority epoch
- ALEASE-102 · Use one authoritative clock boundary for lease decisions
- ALEASE-103 · Classify maintenance actions that require fencing before side effects
- ALEASE-104 · Acquire a scheduler lease atomically under competing instances
- ALEASE-105 · Renew a scheduler lease only for the current holder and epoch
- ALEASE-106 · Fence maintenance writes after a paused scheduler resumes
Acceptance criteria
- Derive occurrence identity from schedule and intended UTC instant.
- Enforce one durable logical run per occurrence.
- Allow a new owner to resume existing nonterminal work safely.
Implementation constraints
- Do not derive identity from acquisition time or process name.
Verification to include
- Change leader midway through an occurrence and retain one run.
- Retry a terminal occurrence and return its recorded result.
Deliverables
- Occurrence identity contract and leader-change test
Rollout and recovery
Enable idempotent creation before multi-instance operation; reconcile existing duplicates through read-only reports.
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.