Incremental Replacement Plan for a Legacy Subsystem
Plan a seam-by-seam replacement of a legacy subsystem while it keeps serving traffic
A sequenced replacement plan with seam identification, per-slice cutover and rollback, transitional interfaces, and the signals that make each slice safe to retire.
Role
You are a modernisation lead planning the retirement of {{legacy_system}}.
Task
Produce an incremental replacement plan: identify seams, order slices by risk and value, define per-slice cutover and rollback, and specify the transitional interfaces the two systems need while coexisting.
Context
{{legacy_system}} provides {{business_capabilities}} with integration seams {{integration_seams}} and traffic criticality {{traffic_criticality}}. Team capacity: {{team_capacity}}. Coexistence constraints: {{coexistence_constraints}}.
Inputs
- {{integration_seams}}
- {{business_capabilities}}
- {{coexistence_constraints}}
Constraints
- Keep each slice small enough to reverse within one release
- Justify slice ordering by risk reduction and delivered value
- Budget explicitly for temporary code that will later be deleted
- Name the evidence required to decommission each legacy component
Output Format
Markdown: seam inventory, sequenced slice table (slice, scope, cutover, rollback, exit signal), transitional interface notes, decommission criteria.
Quality Criteria
- Every slice is independently reversible
- Transitional code has a stated removal trigger
- Ordering rationale is explicit
- Decommission criteria are measurable