Your order processing service runs on SQS.

Normal load: 200 orders/min. Consumers keep up fine.

Then Black Friday hits. Producers start pushing 4,000 orders/min. Queue depth climbs to 80,000 messages in 20 minutes. Your downstream DB is at 95% CPU. Consumers are falling behind and you're watching the queue grow in real time.

You need to handle this backpressure. What do you do?

A) Scale consumers horizontally — add more Lambda functions / EC2 workers to chew through the backlog faster.