It is 3AM. PagerDuty goes off. The payment service is down in production, and the first thing you type into the terminal says more about your seniority than anything on your CV. "Walk me through how you would debug it" is one of the most common senior DevOps and SRE interview questions precisely because it cannot be memorised: interviewers are listening for a repeatable mental model, not a list of commands.

This post walks one realistic incident end to end, the way you would narrate it in an interview or actually run it during an outage. If you prefer watching it as a live terminal walkthrough, the video version covers the same incident:

The incident

Your team deployed a new version of the payment service 45 minutes ago. Three replicas, but only one pod is serving traffic. Users are hitting 503s. You have kubectl access to the prod cluster, no dashboards pre-loaded, and no runbook for this specific failure.…