nginx redirects users to backend address on rare occasions

Chris Ostmo

12/6/22, 8:38 PM

We have an pretty standard nginx, Apache and PHP-FPM reverse proxy setup on Ubuntu 20 installed through ServerPilot.

Our nginx location context is configured simply as this:

    proxy_pass      $backend_protocol://$backend_host:$backend_port;
    add_header      'Access-Control-Allow-Origin' '*';

Those variables resolve to http://127.0.0.1:81

The site has been working flawlessly for several weeks and thousands of users.

However, we have two users who were accessing the frontend address (e.g. https://example.com), and for some reason I cannot discern, were redirected to the backend address and received this browser error.

When these users do any of the following, loading the home page works as expected:

Open the Network Console and check "Disable cache"
Load the site in Incognito mode
The user goes to https://example.com/index.php (which is the only possible index page for the request)

However, even after successfully loading the home page through any of these methods, after quitting the browser and re-opening, the behavior returns - attempts to load the home page without 'index.php' get redirected to the backend server address for the two users.

My two questions:

What could be causing this to happen, and very rarely?
How can we clear this condition for users who are affected without having them dump their entire browser cache (which I'm not 100% confident will work anyway)?

0 + 1

nginx

reverse-proxy

php-fpm

Michael Hampton

12/10/22, 11:01 PM

Why do you believe this has anything to do with nginx? Such problems are usually caused by the backend application. Though in your case it could be Apache.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: nginx redirects users to backend address on rare occasions

TH: nginx เปลี่ยนเส้นทางผู้ใช้ไปยังที่อยู่ส่วนหลังในบางโอกาส

RO: nginx redirecționează utilizatorii către adresa backend în rare ocazii

RU: nginx в редких случаях перенаправляет пользователей на серверный адрес

VI: nginx chuyển hướng người dùng đến địa chỉ phụ trợ trong những trường hợp hiếm hoi

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