Weeknotes

Weeknotes for the week finishing Friday, 10th April 2026.

This week, I:

• Fixed a bug in production. The SSL certificate didn’t automatically renew. It expired, leaving a Cloudflare “Invalid SSL certificate” message in place of OpenPrescribing v2 for about 40 minutes early this morning.
• Started work on a new feature: the ability to query by form/route and ingredient in OpenPrescribing v2’s backend. (Peter added the ability to fetch/ingest dm+d data and to fetch/ingest a mapping from dm+d codes to BNF codes.) I didn’t finish work on it this week, because of the bug in production.
• Finished reading Simon Willison’s guide to Agentic Engineering Patterns.

Another bug in production

I fixed a bug in production last week, too. I’m not concerned that they exist or that they caused long outages; not today, anyway. OpenPrescribing v2 is still beta, signalled by the subdomain and the banner at the top of the page.¹ It takes time to fit together two reverse proxys (Cloudflare, Nginx), SSL certificates (Let’s Encrypt), a web server (Gunicorn), and a web application (Django). Sometimes, a long time: it’s likely that today’s bug was caused by a change I made nearly two months ago in response to an issue with OpenPrescribing v1.

More than last week, this week I leaned heavily on ChatGPT. I asked it to suggest reasons for the error, based on the message and code. I asked it about Dokku and the Let’s Encrypt plugin, because it wasn’t clear to me whether the error originated at the system-level or the app-level. And when the fix we — yes, ChatGPT and me — agreed on didn’t work, I asked it about Cloudflare’s reverse proxy. At this point, however, I ignored its suggestions to disable Cloudflare’s reverse proxy and to use DNS-01 rather than HTTP-01, and instead added a Cloudflare security rule.

Time’s up!