Topics / Engineering practice
Migrate a critical service with an explicit preservation contract.
Name the promises that survive the move, gather evidence at the boundaries and keep the cutover decision separate from implementation completion.
Identify what consumers rely on.
Start with APIs, stored data, event formats, timing expectations and failure behavior. Recover undocumented dependencies from callers, incidents and operators. Mark inferred expectations as candidates until an accountable owner confirms them.
Illustrative example
The new service is correct, but old events remain.
A replacement validates its new schema perfectly. The queue still contains events written by the previous version. Migration evidence needs mixed-version and replay scenarios, not only tests of new events on a clean installation.
Make the transition observable.
- Record the old and new versions and the agreed behavior delta.
- Exercise representative persisted data and queued work.
- Check duplicate delivery, partial migration and restart.
- Decide which mismatches block cutover.
- Define operational observation and rollback conditions.
- Retain the evidence used to authorize the transition.
A rollback plan also needs scrutiny: some data transformations or external effects cannot simply be undone by restoring the old binary.
Use the graph to keep the agreement connected.
Proof links requirements, dependencies, code and evidence so the migration’s preservation obligations remain available to engineers and agents. Incomplete mappings remain a limit on the assessment.
Begin with one consumer boundary and an executable comparison. Expand the scope as concrete dependencies appear, rather than claiming the entire migration is safe from one green suite.
Try it on your software
Bring the riskiest boundary in your migration.
We will identify the preserved promises, transition scenarios and unresolved decisions.