Nodejs app gives 502 error if cloudflare proxy is turned on

[sisindrymedagam]

I have hosted an Angular SSR (NodeJs) application in my IIS (Windows VPS).

It is working if Cloudflare Proxy is turned off. But if Cloudflare Proxy is turned on it shows the 502 error, please find the attached screenshot for the same.

Please help with it. we are on live.

[matteo]

There is no screenshot attached, but…

The 502/504 errors are caused by a problem connecting to an upstream server - meaning your server is trying to initiate a process and this fails to work as expected or times out. In most cases of 502 / 504 errors, back-end servers are not communicating correctly. When this happens, you will see color page with Cloudflare branding and the Error 502 Bad Gateway or Error 504 Gateway Timeout. Review this Community Tip for fixing 502 or 504 gateway errors.

[ngocbauofficial]

I also have the same problem

[ruslan.novikov]

Same problem in several of my projects.
It doesn’t depend on my servers.

Some websites are slow and Cloudflare gives 502 or 504 gateway errors. Other websites on the same server through Cloudflar are fast.

I enabled “Development Mode. Temporarily bypass our cache. See changes to your origin server in realtime.” Gateway error goes away!

[sisindrymedagam]

I have found the root cause for this. If I enable Full or Full (strict) SSL modes in Cloudflare. I’m getting a 502 error. But my server has already been configured with the Let’s Encrypt certificate.

Can someone have a solution for this?

[erictung]

@sisindrymedagam

But my server has already been configured with the Let’s Encrypt certificate.

Is your server allowing port 443 traffic from Cloudflare?

[sisindrymedagam]

@erictung

Is your server allowing port 443 traffic from Cloudflare?

Yes, Here I am allowing 80, 443 ports

And Scope set to Any IP Address.

Have any thoughts?

[sandro]

@sisindrymedagam

if I put it as flexible, the app ends up with a redirect error.

You shouldn’t be using that in the first place.

Why you should choose Full Strict, and only Full Strict

Unencrypted & unverified connections Imagine you open Paypal and suddenly get that warning [image] Would you continue? Probably not. For decades leaders in IT security have advocated that people upgrade their sites from unencrypted HTTP to secure HTTPS. And for a reason, everything you send via an HTTP connection is sent in plain text and can be intercepted at any point between you and the server. Equally, you’d probably not proceed if you got such a warning, right? [image] That’s when th…