hardScenarioCase StudySeniorStaffLead
You have inherited a system nobody left behind any knowledge of, and you have two weeks to produce a plan. Walk me through it.
6 min readUpdated 2026-08-15
Answer
Short answer
Spend the first week building an evidence map from money, traffic, incidents and deploys rather than from code, and interviewing the people who touch it with one fixed set of questions.
Legacy systems need discovery before redesign. Good discovery starts with runtime facts: traffic, data stores, batch jobs, owners, incidents, and the paths users actually depend on. Weak legacy systems answers propose a rewrite before discovery has shown what the system is for. Strong legacy systems work turns discovery into a risk map, then uses that map to decide what to stabilise, document, retire, or replace.
Strong legacy systems work also explains how legacy systems became risky, so the team can avoid recreating the same blind spots.
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Likely follow-ups
- Nothing is instrumented and you cannot deploy safely. What is the first change you make?
- Your plan says do not rewrite. How do you hold that line when the team wants to?
- Two weeks in, you find an undocumented nightly job that feeds finance. How does the plan change?
- Who signs off this plan, and what do you need from them to make it real?
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