The Constant Frozen at Boot Bug: A Ruby Exercise For An Interview

Wed, 10 Jun 2026 00:00:00 +0000

I like interview questions that come from real incidents instead of a puzzle book. You can’t google your way out of them, and the candidate’s reasoning maps directly onto the job. This one came from a payment service. It looks trivial. It is not.

I’ve stripped the production code and rebuilt the same shape around a fake payment router. The bug is identical; the names are not.

The Question

Here is a class that routes payments to a gateway. Occasionally a charge is
written to the database with method_id = NULL, even though the payment method
clearly exists in the payment_methods table. No exception is raised. The only
thing that reliably fixes it is restarting the process. Find the bug.

Ruby IO buffering

Fri, 16 Jan 2026 00:00:00 +0000

Your Kibana/Cloudwatch/Grafana have different timestamps, you don’t see recent logs from your application. Why is that? You may ask. Some QA reports that your application is not working/was not deployed, asking you to review the deploy process. Or even worse: asking your devops colleagues to “something went wrong” with last deployment could you check?

You login into your shell running kubectl get pods to verify timestamps update or checking Helm releases helm ls. But everything seems fine, everything deployed. CI/CD is green, all timestamps updated. But yet. QA does not see the logs. Where have they gone?

Rails on @zhisme :: signal over noise

The Constant Frozen at Boot Bug: A Ruby Exercise For An Interview

The Question

Ruby IO buffering