Do not roll back a worker into an unreadable job format
Worker v8 enqueues a new payload shape. Rolling back to v7 starts a retry storm because v7 cannot parse jobs already accepted by v8.
- Focused work estimate
- 5h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Message evolution · Rollback safety · Queue operations · Compatibility contracts
Estimated field mix
- Platform engineering60%
- Distributed systems40%
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 scheduling service has an API, a worker, and PostgreSQL. Releases use immutable images on two application instances. The team needs compatibility checks, staged traffic, and a rehearsed rollback without introducing a new orchestration platform.
Setup prerequisites
- HTTP health checks
- CI pipelines
- Database migrations
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Version job envelopes and declare the worker versions able to consume each version.
- Gate rollback when queued work would become unreadable.
- Provide a safe drain or compatibility path that preserves accepted job identities.
Implementation constraints
- Do not rewrite historical payloads in place or discard incompatible jobs to make rollback green.
Verification to include
- Process old and new fixture envelopes with the declared compatible worker.
- Attempt an incompatible rollback with queued v8 work and assert a useful blocking reason.
Deliverables
- Job compatibility matrix and rollback preflight
Rollout and recovery
Deploy backward readers before new writers; remove old readers only after the compatibility window closes.
Value of the work
For the engineer: Practice release contracts, compatibility windows, measurable canaries, and incident decisions on a modest application topology.
For the team: Review whether an engineer can make deployments diagnosable and reversible while identifying when rollback is unsafe.
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.