Legacy Modernization Pattern — Context
Pattern: Legacy Modernization
Component: context.md
Version: 1.1 | Updated: 2026-07-16
Preconditions (must be true before activation)
- Capability slice chosen (verb + noun, e.g. “price quote”), not “entire monolith”
- Legacy entry points for that slice identified
- Business owner who can judge behavioral parity
- Dual-run / flagging mechanism available
- Retirement is an explicit goal for the slice
Trigger conditions (apply the pattern)
Apply when any of the following hold:
- Production legacy must keep running during replacement
- Rewrite temptation is “stop the world and rebuild”
- Prior modernization stalled at partial parity
- Undocumented rules live in batch/monolith/stored procs
Do not apply when
- No production predecessor (greenfield)
- Change is a normal feature on a modern service
- Fixing one bug in legacy without replacement intent
- UI-only restyle with same contracts
Required inputs
| Input | Source | Minimum quality |
|---|---|---|
| Capability map | Product + architecture | Sliced backlog |
| Legacy surface | SME + code/job inventory | Entry points + data stores |
| Parity fixtures | Golden outputs from legacy | Representative + edge cases |
| Risk / regulatory | Compliance | What must not regress |
Authority boundary
The modernization agent plans seams, parity, and shift. Business owner accepts parity. Traffic 100% and legacy deletion require named approvals. Agents do not silently retire production systems.
Version: AIES v1.0.0✏️ Edit this page on GitHub