Failed certificate renewals are a classic engineering grind that can quietly break your site. The HTTP-01 challenge usually fails due to subtle routing and infrastructure misconfigurations.
Here is what breaks your renewals:
The problem: Forgotten AAAA IPv6 records, restrictive CAA policies, or CDN features like Cloudflare Bot Fight Mode blocking challenge requests.
The fix: Ensure your request path correctly forwards challenge traffic and set up early alerts for renewal failures.
Why it matters: Understanding how the HTTP-01 challenge moves through your stack prevents surprise downtime and saves you from emergency SSL debugging.
Check out the full technical write-up to learn more about troubleshooting certificate renewals:
Why Let's Encrypt certificate renewals fail - Upsun Developer
Certificate renewals fail for a handful of recurring reasons. Here's how the HTTP-01 challenge works and what breaks it, from IPv6 records to CDN rules.
developer.upsun.com
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