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Let's Encrypt Errors and Solutions

What will you learn in this guide?​

This guide covers common SSL and DNS errors encountered when using Let's Encrypt.
You learn how to diagnose and resolve these errors on Nginx and Ubuntu.
The goal is to complete HTTPS configuration quickly and accurately.

Technical Summary​

Main topic: Troubleshooting Let's Encrypt SSL errors
Solved problem: DNS, firewall and certificate problems occurring during HTTPS installation
Gain: Stable and secure HTTPS configuration

Steps followed:

  1. Verify DNS records
  2. Resolving certificate expiration and renewal issues
  3. Troubleshoot mixed content errors
  4. Resolving Certbot connection and firewall errors
  5. Checking manual HTTPS configuration

1. Checking DNS Records​

Most Let's Encrypt errors are caused by DNS.
Your domain name must be pointed to the correct IP address.

Test DNS resolution​

nslookup ornek.com
  • This command shows which IP address the domain name is resolved to.
  1. DNS changes may not propagate immediately.
  • The propagation time is usually between 5 and 30 minutes.

If the TTL value is high, propagation takes longer. TTL may be temporarily lowered during testing.

2. Certificate Expired Errors​

  1. Let's Encrypt certificates are valid for 90 days.
  • Non-renewed certificates produce browser errors.
  1. Renew the certificate manually

sudo certbot renew --nginx -d ornek.com -d www.ornek.com
  • This command renews existing certificates.
  1. After the refresh, Nginx can be restarted.

sudo systemctl restart nginx
  • This command enables new certificates to become active.

3. Mixed Content Errors​

  1. If HTTP content is called within an HTTPS page, the browser issues a warning.
  • This situation is usually caused by proxy or old links.
  1. Add Nginx SSL redirect headers

location / {
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-Host $host;
    proxy_set_header X-Forwarded-Proto https;
}
  • These settings pass HTTPS information to the backend application.

Additionally, all asset connections must be HTTPS.

4. Certbot Timeout and Firewall Errors​

  1. If Certbot cannot reach the server during verification, the process will fail. This situation is usually caused by the firewall.

  2. Open the required ports


sudo ufw allow 'Nginx Full'
  • This command opens ports 80 and 443.

Then run certbot again.


sudo certbot --nginx -d ornek.com
  • If attempts are made too frequently, a temporary limit will be applied. In this case, approximately 1 hour should be waited.

5. HTTPS Not Working But No Error​

Certbot may have obtained the certificate. However, Nginx configuration may not have switched to HTTPS.

  1. Basic HTTPS configuration example

listen 443 ssl;

ssl_certificate /etc/letsencrypt/live/ornek.com/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/ornek.com/privkey.pem;

if ($scheme != "https") {
    return 301 https://$host$request_uri;
}
  • This configuration listens for HTTPS and redirects HTTP.
  • Test the changes.

sudo nginx -t
sudo systemctl restart nginx
  • These commands verify and apply the configuration.

Frequently Asked Questions​

1. DNS is correct but certbot gives an error, why? DNS propagation may not be completed.

2. What happens if the certificate is not automatically renewed? Browsers show the site as unsafe.

3. Is the mixed content error dangerous? Yes, it lowers the browser security level.

4. Is it enough to open only 443? Usually 80 is also required for verification.

Result​

Let's Encrypt errors are mostly caused by DNS and configuration. With the right controls, these problems can be resolved quickly. Once the HTTPS configuration is completed, your site is secure.

You can easily implement these processes in the GenixNode infrastructure.