Let's Encrypt Auto-Renewal Failed? Here’s How to Fix It.

Let's Encrypt has revolutionized web security by providing free, automated SSL certificates. However, their certificates are only valid for 90 days. You are meant to rely on automated scripts (like Certbot) to renew them every 60 days.

But what happens when that automated script fails? Your site goes offline, your visitors see a scary warning, and you lose revenue.

Top Reasons Why Let's Encrypt Renewals Fail

1. Port 80 is Blocked

Let's Encrypt uses the HTTP-01 challenge to verify that you own the domain. This challenge requires your server to respond to a request on Port 80 (HTTP). If you recently tightened your firewall rules and completely blocked port 80 (forcing everything to 443), the Let's Encrypt bot cannot reach your server to verify ownership, and the renewal will fail.

2. DNS Changes or Cloudflare Proxy Issues

If you recently moved your DNS to Cloudflare and turned on the orange "Proxy" cloud, the IP address Let's Encrypt sees no longer matches your origin server. You may need to use the DNS-01 challenge or Cloudflare's Origin Certificates instead.

3. The Cron Job is Missing or Broken

Sometimes, the server gets restarted or updated, and the crontab that triggers `certbot renew` gets wiped out. If the script never runs, the certificate simply expires.

How to Fix the Issue

1. Run a Dry Run: SSH into your server and run certbot renew --dry-run. This will simulate a renewal and print out the exact error message.
2. Check your Firewall: Ensure port 80 is open to the public internet.
3. Verify DNS: Make sure your domain's A record points exactly to the IP of the server requesting the certificate.