Cross-tenant data leak
A multi-tenant SaaS shards data by `tenant_id`; every write must include it as the partition key. At 11:00 a feature flag enabled a new 'fast path' write handler for 5% of traffic. By 11:40, support escalates: a few tenants see *another tenant's* records appearing in their lists, and some of their own new records are 'missing'. Dashboards: write success 100%, error rate flat, no auth failures. The new handler derives `tenant_id` from a cached request context. How do you triage, stop the cross-tenant contamination immediately, and remediate?
What a strong answer looks like
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.
0:00 of about 40 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.