Build a Message Queue (RabbitMQ / SQS) (14 scenes)
Scene 12

Operations — depth, age, DLQ

In production, three numbers tell you a queue's health: visible depth, oldest-message age, and DLQ depth — each one points at a distinct underlying failure.

Previously

We've built the queue end to end. Now invert: an operator sees only three dashboards. Which one moves first, and what does each one mean?

Scene 12

Operations — depth, age, DLQ

  1. Watch
  2. Try it
  3. Predict
  4. Capture
scenario: baselineQUEUE DEPTH (visible)200last 5 minutesdepth flat → producer/consumer rates balancedOLDEST MESSAGE AGE5sage low → head is movingDLQ DEPTH0redriveDLQ empty → no terminal failures
Kafka's analog is consumer lag (per partition, per group); queue depth and oldest-age are the broker-side equivalents because the broker, not the consumer, owns position.
What to watch for

Three incidents in sequence: a traffic spike, a stuck worker, then a poison wave from a bad schema deploy. Watch which meter moves under each — the mapping is the whole lesson.

Continue unlocks when the animation finishes.

Where this sits in Build a Message Queue (RabbitMQ / SQS)

Scene 12 of 14. Three numbers tell you a queue's health: visible depth, oldest-message age, DLQ depth. Each one points at a distinct underlying failure.

Up next. You can name the failure mode from the meter. Final move: stop being told the workload, and design the queue yourself.

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