Welcome emails delivered multiple times
A `welcome-email` worker consumes a Pub/Sub subscription and calls an email provider's send API per message. At 17:00 support gets a wave of 'I received the same welcome email 3–4 times' complaints. Dashboards: the subscription's `oldest_unacked_message_age` is elevated and redelivery is high — `ack_message_count` is healthy but the *delivered/ack ratio* is well above 1; worker CPU and the email send latency both crept up after a deploy at 16:50 that added an analytics call into the send path. The ack deadline is 60s. How do you triage and mitigate?
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 35 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.