Intermittent 521 Cloudflare/Azure

I am getting an intermittent 521 Cloudflare page when accessing my azure app.

  • The cf 521 error page returns immediately.
  • If I bypass cloudflare, i.e. access the server directly via * I get no error.
  • It just started happening after no changes to server.
  • If I reload the page, it immediately works again (so I’m pretty sure this is not an actual 521)
  • I don’t see any error in server logs

I am thinking it is related to a config problem, there is a single cloudflare proxy doing something bad. @stefano1
Any help is appreciated.

Seeing the same thing here with one of our domains. Intermittant 521s that immediately go away with a refresh.

If you’re using Azure, I think I managed to fix it by going into the Azure Tsl/Ssl settings and creating a binding that binds to the Cloudflare private cert. and enabling https on.

Hope this helps you.

edit: did not fix but it seems way more intermittent now - i’m just disabling cf proxy now.

Disabling cf proxy is the fix, haven’t seen error in 2 days.

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Hello Alan,

we might need to record that to a ticket, directly on your website, do you mind open a ticket and paste the number here,

@jjb could you also open a ticket?

the ideal here is to create a test sub-d, domain, proxied with CF, please check: