Describe a time you led a significant technical initiative — architecture, delivery, and trade-offs

Model answer

STAR structure for system-level leadership. Situation: legacy PHP monolith handling 2M daily active users was causing 4-hour deployment cycles and frequent database deadlocks. Task: lead the extraction of the authentication subsystem to a standalone Go service — first step of a broader decomposition strategy. Action: (1) defined the service boundary using domain events — auth emits UserLoggedIn, SessionCreated events; downstream systems subscribe. (2) Designed a strangler fig migration: ran the Go service in shadow mode alongside PHP for 2 weeks, comparing outputs. (3) Managed stakeholder concerns about risk by presenting a rollback plan (feature flag to route traffic back to PHP in <30 seconds). (4) Mentored two mid-level engineers through their first microservice design review. Result: Go auth service handling 100% of auth traffic 6 weeks later, p99 latency dropped from 120ms to 18ms, zero incidents during cutover. Key lesson: the technical part is often easier than the organisational part — invest in communication and rollback plans.