Intermittent Error 520, host says nothing in logs, Always Online off


I’ve been having seemingly random intermittent error 520 on my site for months. It shows up on any platform, any time, one refresh and it’s gone. My host, Steadfast, says everything looks fine on their end, and nothing shows up in the logs, even when I send them timestamps of the errors.

  • Steadfast assures me that all CF IPs have been white listed, triple verified. Additionally, both mod_cloudflare and mod_remoteip are installed and enabled. As well as the Interworx plugin for Cloudflare…

  • I have Always Online off, and I still get 520s.

  • I’m on the free CloudFlare plan. I upgraded to Pro a few months ago to get CoudFlare to help with the issue, but they assured me it was a problem with my host. I’m not using any load balancer. HTTP/2 is forced on, I cannot disable it

  • I’ve followed the Community Tip here: Community Tip - Fixing Error 520: Web server is returning an unknown error

  • An example of a Ray ID from an error 520 on would be 67e3bac58822f555 timestamp 2021-08-13 17:40:37 UTC

  • I cannot prepare HAR files since the error is intermittent and so far impossible to reproduce on purpose.

Any help is greatly appreciated!

I forgot to include the trace result:

uag=Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.131 Safari/537.36

@rollergirl , welcome to the club! Here’s the main thread on the issue: Sometimes a CF 520 error

After enduring a lot of complaints from customers, I removed the CF, I’m doing several tests and so far, no 520 error.

Thanks, but that thread said it was solved on August 11th. I’m still having error 520. I got one myself yesterday.

Same here! The sudden increase of 520 errors started about 3 weeks ago for me. I haven’t experienced them myself on the front end, but you can see that stat in your account, and for me it’s about 2% percent of the requests that return 520, which is huge.

For some reason, this stat is buried deep in the interface. To check it, you need to go to support center, then click “Submit a request”, and then click on “Error Analytics”.

Looks and sounds like it’s just an issue with Mozilla version 5.0, cause I’m using chrome 93.0.4577.36 (Official Build) beta (64-bit) version and it loads for me!

@rollergirl Use a different browser or update your browser (it seems it’s working for me and I’m using chrome)

Have you followed these steps
Error 520: web server returns an unknown error
Error 520 occurs when the origin server returns an empty, unknown, or unexpected response to Cloudflare.


A quick workaround while further investigating 520 errors is to either grey cloud the DNS record in the Cloudflare DNS app or temporarily pause Cloudflare.
Contact your hosting provider or site administrator and request a review of your origin web server error logs for crashes and to check for these common causes:

Origin web server application crashes
Cloudflare IPs not allowed at your origin
Headers exceeding 32 KB (typically due to too many cookies)
An empty response from the origin web server that lacks an HTTP status code or response body
Missing response headers or origin web server not returning proper HTTP error responses
520 errors are prevalent with certain PHP applications that crash the origin web server.
If 520 errors continue after contacting your hosting provider or site administrator, provide the following information to Cloudflare Support:

Full URL(s) of the resource requested when the error occurred
Cloudflare cf-ray from the 520 error message
Output from (replace with your hostname and domain where the 520 error occurred)
Two HAR files:
one with Cloudflare enabled on your website, and
the other with Cloudflare temporarily disabled.

The problem is intermittent, in only happens sometimes, seemingly randomly. Not just for me, for our visitors as well and they are on multiple browsers and platforms.

I have followed the tip you posted. the only thing I cannot provide are the HAR files since I cannot reproduce the error on demand.


Calling in the infantry on this one: ticket number 2224284 @MoreHelp

Are there any remaining problems with error 520s on the free zones?

If not, what should I do next?

I too keep having this issue, i’m not sure why. But when i have this issue, i jsut need to login to cloudflare and the problem just mysteriously solved. What is the main issue?

I’m not sure what the issue is. That’s why I’m posting here.

Well, not necessarily related, but I upgraded my account to the Pro level to get some help from CloudFlare support, because they weren’t responding to the @MoreHelp tag, and I’ve had no errors since…

We have just received an update that the continued 520s do not look like a Cloudflare issue, as there was before. Cloudflare Status - Elevated 520 errors on Free Zones is now resolved.

If you are still receiving 520s, they are likely caused by an issue on your origin server. Please follow the guidance in the #CommunityTip and Support Center.

1 Like

I’m having 520 errors intermittently since Aug 27, 2021.
All 520 errors only from the Los Angeles cloudflare datacenter.
Anyone with the same issue?

I’ve been getting the same 520 errors described here and in other threads as well, I started noticing the error probably sometime in July.

Just like a lot of people have described, the Error 520 are intermittent, and I often get hit with the error with fast clicks.

I spent the past 4 days investigating the problem on our side, but the result is inconclusive. Nothing showed up in server logs, SSL all working, server load is pretty light and consistent with few months prior. I can’t even reproduce the error consistently. What’s going on Cloudflare?

Ray ID: 686d6a934c78fb98

uag=Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.159 Safari/537.36

My 520 errors are 100% from Los Angeles datacenter.
Ray IDs:

Ray ID: 686e4f336c0a5275
Ray ID: 686dfd4a5b76eb49
Ray ID: 686de999ad055214
Ray ID: 686d832afbcd0d34
Ray ID: 68662023caa2eb14
Ray ID: 686641c46fc2312e
Ray ID: 686641ca9b90312e
Ray ID: 686641cabbc5312e

Out of curiosity, where is your site hosted? I go through LAX and I can’t remember the last time I’ve seen a 520 on any site.

The server is an EC2 located in the N. Virginia AWS datacenter (us-east-1 region). And it’s running HAProxy 2.4.3.

The errors are randomly, the major of requests works great. But the request that respond with a 520 errors, 100% of that requests came from the LAX cloudflare datacenter. All other CF datacenters works perfectly.

This start happening since Aug 27, 2021.