If you have hosted your website on Cloudflare CDN then you or your visitor may have experienced the following problem on their browser.
A 522 error happens when a TCP connection to the web server could not be established. To initiate a TCP connection the Cloudflare edge server sends out 3 SYN packets and awaits a SYN-ACK packet in return, if it doesn’t receive one within 15 seconds the connection attempt will fail.
Common reasons for Cloudflare to not receive the SYN-ACK in return:
- Our connection attempt was blocked by a firewall/security plugin at the host
- Packets are being dropped within the host’s network
- The origin server was too overloaded to respond
- There was an issue with an upstream provider along the path
The most common solutions to the above problems are
- You should whitelist CloudFlare IP ranges to ensure this doesn’t happen. You can check this page on Cloudflare for the list of IP addresses.
- Check and lower load of the server if it is too high
Hope the above helped.