Postmortem: How a Let's Encrypt Certificate Expiry Took Down Our Nginx 1.26 Sites for 1 Hour in 2026

On January 12, 2026, at 09:17 UTC, every Nginx 1.26 instance in our global fleet serving 14.2 million monthly active users stopped accepting TLS connections for 58 minutes and 42 seconds. The root cause? A Let's Encrypt certificate that expired 11 mi...