Subject Matter Expert (SME)

## The Hands on the Keyboard If the **Incident Commander** is the conductor, the **Subject Matter Expert (SME)** is the soloist. They are the engineer who knows *exactly* why the Redis queue is backing up or why the load balancer is throwing 502s. ### Responsibilities - **Diagnosis**: finding the root cause. - **Mitigation**: stopping the bleeding (e.g., adding capacity, rolling back). - **Communication**: telling the IC what they are doing *before* they do it. ### How to be a Great SME The best SMEs don't just fix things; they **communicate**. * **Bad SME**: Goes silent for 20 minutes, then says "Fixed it." * **Good SME**: "I suspect a bad migration. I am going to verify the schema version. (5 mins later) Verified. I requested permission to rollback." ### One Area of Focus An SME should focus on **one** thing. If the incident spans multiple services (e.g., Database + Frontend), you need multiple SMEs. The IC coordinates them; the SMEs fix the systems.