Derby ticket sales open: 4 purchases out of 10 fail with “try again later”

Tadakir (a fictional sports ticketing company) opened the sale of the 45,000 seats for the 25 October derby at 12:00. Purchases go through the Lambda function tadakir-achat, which decrements the seat stock in the DynamoDB table tadakir-billets and then records the ticket.

The table is in on-demand mode “precisely to absorb peaks”. Since 12:01, about 40% of purchases fail: the application shows “Heavy traffic, try again later” and fans keep retrying. The CTO wants to “switch the table to provisioned at 50,000 WCU”.

You are on your workstation with the AWS CLI v2 (region eu-west-1). The ticketing runbook is in your home directory.