When Cloudflare faces outages or routing issues, millions of websites experience failures ranging from 500 errors to SSL problems to connection timeouts.
However, not all errors mean Cloudflare is down — many originate from the origin server or misconfigurations in your Cloudflare dashboard.
This guide provides step-by-step solutions for website owners, developers, and server administrators to quickly diagnose and fix Cloudflare-related errors.
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1. Fixing “500 / 502 / 503 / 504” Errors
These errors normally indicate a problem on your origin server:
✔ Solutions
Restart your web server (NGINX/Apache)
Check server error logs
/var/log/nginx/error.log
/var/log/apache2/error.log
Increase PHP memory + max execution time
Optimize database (MySQL/MariaDB)
Disable heavy plugins (if using WordPress)
Check for high CPU or RAM usage
Verify hosting uptime — the provider may be down
🛠 Why It Happens
Cloudflare attempts to connect to your server but receives an invalid or delayed response.
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2. Fixing “Error 520 – Web Server Returned an Unknown Error”
This is a Cloudflare-specific error, usually caused by unexpected origin behavior.
✔ Solutions
Temporarily disable “Under Attack Mode”
Turn off WAF rules one by one to identify conflicts
Remove problematic Page Rules
Disable Rate Limiting
Check headers returned by the origin server (Cloudflare rejects malformed headers)
Ensure your server isn’t blocking Cloudflare IPs
🛠 Why It Happens
The origin returns something Cloudflare cannot interpret (bad headers, empty response, etc.).
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3. Fixing “521 – Web Server Is Down”
Cloudflare reaches your IP, but your server refuses the connection.
✔ Solutions
Whitelist all Cloudflare IP ranges in your firewall
https://www.cloudflare.com/ips/
Restart web server
systemctl restart nginx
systemctl restart apache2
Check iptables / UFW / CSF for blocked Cloudflare IPs
Verify your server is listening on port 80 and 443
netstat -tlnp
🛠 Why It Happens
Firewalls or security plugins block Cloudflare’s requests.
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4. Fixing “522 – Connection Timed Out”
Cloudflare connects but the server takes too long to respond.
✔ Solutions
Increase server timeout settings:
NGINX → proxy_read_timeout 300;
Apache → Timeout 300
Optimize slow MySQL queries
Upgrade server CPU/RAM if overloaded
Disable brute-force plugins or bot blockers
Ensure port 443 is open and not rate-limited
🛠 Why It Happens
The origin server is slow, overloaded, or under attack.
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5. Fixing “525 – SSL Handshake Failed”
Cloudflare and your origin cannot complete SSL verification.
✔ Solutions
Install a valid SSL certificate (Let’s Encrypt recommended)
Set SSL Mode to:
Full (strict) if your origin has a valid cert
Full if it has a self-signed cert
Check server date/time (SSL requires correct time)
Restart NGINX/Apache
Remove outdated TLS protocols (use TLS 1.2/1.3)
🛠 Why It Happens
Mismatch between Cloudflare SSL mode ↔ your server setup.
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6. Fixing “1020 – Access Denied”
Cloudflare Firewall is blocking visitors.
✔ Solutions
Go to: Security → Events
Identify what rule triggered the block
Remove or adjust strict firewall rules
Lower Bot Fight Mode sensitivity
Add country or IP range exceptions
Review:
WAF managed rules
Custom rules
Rate-limiting rules
Access Rules
🛠 Why It Happens
Overly restrictive security rules accidentally block legitimate traffic.
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7. Fixing DNS Issues
If DNS is misconfigured, Cloudflare won’t connect to your host.
✔ Solutions
Ensure DNS records (A/AAAA/CNAME) point to correct IP
Check if your hosting provider changed your server IP
Disable “DNS Only” for proxied traffic (turn Cloudflare orange)
Avoid circular CNAME references
🛠 Why It Happens
Incorrect IPs, deleted DNS entries, or misconfigured records.
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8. Fixing High Traffic or DDoS Overload
If Cloudflare detects abnormal traffic, it might throttle or block requests.
✔ Solutions
Enable Cloudflare Rate Limiting
Turn on Bot Management
Enable DDoS Attack Protection
Use Argo Smart Routing
Use a CDN Cache rule:
Cache Everything
Edge Cache TTL: 1 hour
Enable “Always Online”
🛠 Why It Happens
Sudden spikes overload your origin server, not Cloudflare.
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9. Server Optimization Tips for Cloudflare Users
✔ Enable full page caching
✔ Use Redis instead of MySQL for sessions
✔ Increase PHP-FPM children count
✔ Use object caching (Redis/Memcached)
✔ Upgrade to faster hosting (NVMe / Dedicated / VPS)
Good server optimization = fewer Cloudflare errors.
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Final Thoughts
Cloudflare is extremely powerful, but it requires proper configuration. Most Cloudflare errors are caused by:
Misconfigured server settings
SSL mismatches
Firewall blocks
Overloaded origin servers
Incorrect DNS records
By following the above steps, website owners can quickly restore uptime and prevent future issues — even during large-scale outages.
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