Integrating Legacy Systems

Interview Phase (Critical - Not Optional)

When to Interview: This step is high-risk and often initiated prematurely. Always interview unless the user has explicit organizational buy-in for a freeze agreement AND has already assessed legacy system state and extraction feasibility.

Interview Strategy: Assess organizational readiness, understand legacy system constraints, and validate event extraction feasibility before designing the side-car. Poor planning here leads to costly integration failures.

Critical Questions

Always conduct this interview unless all context is provided:

1. Legacy System State & Documentation (Impact: Determines how much reverse-engineering is needed; affects timeline dramatically)

   • Question: "Tell me about the legacy system: (A) Technology stack, (B) Age/last major update, (C) Database size/complexity, (D) Current users/traffic, (E) Known documentation or audit trails?"
   • Why it matters: Undocumented systems require exploration; modern systems may have better audit logs; scaling affects extraction approach
   • Follow-up triggers: If documentation is incomplete → ask for at least data schema; if no audit trail → ask about update_at timestamps; if very large → ask about partitioning strategy

2. Organizational Freeze Agreement (Impact: Most critical—determines if side-car is even feasible)

   • Question: "Has business leadership agreed to FREEZE the legacy system? Specifically: (A) No new features in legacy, (B) Only bug fixes permitted, (C) No schema changes?"