When Certificates Hide in Plain Sight: A Traefik Mystery

Traefik’s Memory Games: Hunting Invisible Certificate Ghosts

The borisovai-admin project was experiencing a mysterious failure: HTTPS connections were being rejected, browsers were screaming about invalid certificates, and users couldn’t access the system. On the surface, the diagnosis seemed straightforward—SSL certificate misconfiguration. But what unfolded was a lesson in asynchronous systems and how infrastructure actually works in the real world.

The task was to verify that Traefik had successfully obtained and was serving four Let’s Encrypt certificates across admin and auth subdomains on both .tech and .ru TLDs. The complication: DNS records for the .ru domains had just finished propagating to the server, and the team needed confirmation that the ACME challenge validation had completed successfully.

My first instinct was to examine acme.json, Traefik’s certificate cache file. Opening it revealed something unexpected: all four certificates were actually there. Not only present, but completely valid. The admin.borisovai.tech certificate was issued by Let’s Encrypt R12 on February 4th with expiration in May. Everything looked pristine from a certificate standpoint.

But here’s where the investigation got interesting. The Traefik logs were absolutely filled with validation errors and failures. For a moment, I had a contradiction on my hands: valid certificates in the cache, yet error messages suggesting the opposite. This shouldn’t have been possible.

Then it clicked. Those error logs weren’t describing current failures—they were historical artifacts. They dated back to when DNS propagation was still in progress, when Let’s Encrypt couldn’t validate domain ownership because the DNS records weren’t consistently pointing to the right place yet. Traefik had tried the ACME challenges, failed, retried, and eventually succeeded once DNS stabilized. The logs were just a record of that journey.

This revealed something important about ACME systems that often goes unmentioned: they’re built with resilience in mind. Let’s Encrypt doesn’t give up after a single failed validation attempt. Instead, it queues retries and automatically succeeds once the underlying infrastructure catches up. The system is designed for exactly this scenario—temporary DNS inconsistencies.

The real culprit wasn’t the certificates or Traefik’s configuration. It was browser DNS caching. Client machines had cached the old, pre-propagation DNS records and stubbornly refused to forget them. The fix was simple: running ipconfig /flushdns on Windows or opening an incognito window to bypass the stale cache.

The infrastructure had actually been working perfectly the entire time. The phantom errors were just ghosts of failed attempts from minutes earlier, and the browsers were living in the past.

The next phase involves configuring Authelia to enforce proper access control policies on these freshly-validated endpoints—but at least now we know the foundation is solid. Sometimes the best debugging comes not from fixing something broken, but from realizing it was never actually broken to begin with.

What’s the best prefix for global variables? window. 😄