Clodflare site responds as down 5XX, while direct access responds (up)

Hello, I am having a recurring issue where the website fails to respond via cloudflare. For some computers (control group) I have setup a static DNS record to the internet IP address of the website (hosted in a collocation service). When the problem occurs the website via cloudflare fails to respond, on some cases times out and gives the error that the host is down, while the other PCs (control group with statis DNS entry) website accessing the same login page respond instantly. Control group PCs are on the same internet provider, same office, than the ones using Cloudflare DNS and proxy. I’m trying to figure out what is the best way to approach the search of the logs and or metrics that can shed some light into why will this happen. It seems specific to the cloudflare service. The test is to go to the login page, direct static IP DNS resolution to the website works, via Cloudflare it times out, then after several minutes all goes back to normal. Web server metrics all look normal, no excessive loading on any metric. I resulted on turning off proxy DNS and for now, all seems to be working without the issue.

Hello,

Sorry to hear you are having issues. The best way to test this is to grab a HAR file to see what is happening within the browser. When you fire off the request.

With the proxy enabled on the problem machines are you able to dig/nslookup the zone name and have it resolve to Cloudflare IP’s? As it should when the proxy is enabled due to it routing to our edge network.

Are you able to access the zone when the proxy is enabled on a mobile device that is not on the same network? If not what is the error we see when this is tested? Any screenshots or errors would be very helpful. Look forward to hearing from you.

Hello and thank you for the answer. Yes, the machines that have the problem yes they resolve to the Cloudflare IPs and just do not not get a response from the site. If I access another site, on the same cloudflare account, we get perfect response. So seems a site specific issue in cloudflare. While the non responding site problem occurs, I do get access and the site responds instantly on machines with static dns to the website (bypassing Cloudflare proxy). The problems persists with other machines or cell on other machines connected to other Internet providers networks. When the problems occur we tested with different carriers (cell) and different Internet providers. Everything points to an issue with the Cloudflare “proxying” which suddenly stops. We see no up spikes on security logs on the account, nothing glaringly obvious. Not sure if we hit a throttling issue with cloudflare or what the issue is. We turned off proxy for that specific site and problem is no longer happening, but would like to turn on again, we just can’t without getting an answer.