NGINX / Cloudflare random 520 HTTP errors when HTTP2 is enabled within NGINX

TidyDev

11/18/22, 8:07 AM

I'm seeing a problem where Cloudflare returns a 520 HTTP error code to roughly 10% of requests. However the issue does not occur if I bypass the Cloudflare proxy, and request from the server directly.

After lots of troubleshooting, I've discovered if I remove the two http2 parameters after listen, then the issue goes away, and Cloudflare stops returning the 520 errors.

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    ssl_certificate         *path to key*;
    ssl_certificate_key     *path to key*;
    server_name example.com;
    root *path to directory*;
    location / {
        proxy_pass         http://localhost:5000; // proxying asp.net core app
        proxy_http_version 1.1;
        proxy_set_header   Upgrade $http_upgrade;
        proxy_set_header   Connection keep-alive;
        proxy_set_header   Host $host;
        proxy_cache_bypass $http_upgrade;
        proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header   X-Forwarded-Proto $scheme;
    }
}

Is there a resolution to the problem that allows me to keep the HTTP2 capability?

292

1 + 0

nginx

cloudflare

Score:3

Server

Esa Jokinen

11/18/22, 9:42 AM

The easy explanation is that according to the Understanding Cloudflare HTTP/2 and HTTP/3 Support:

Cloudflare only uses HTTP/1.x between the origin web server and Cloudflare.

You can disable the HTTP/2 on your origin server and still benefit from it between the browser and Cloudflare, as it is enabled by default if you have TLS at Cloudflare's edge network.

0 + 0

Elon Musk

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

EN: NGINX / Cloudflare random 520 HTTP errors when HTTP2 is enabled within NGINX

TH: ข้อผิดพลาด HTTP 520 ของ NGINX / Cloudflare เมื่อเปิดใช้งาน HTTP2 ภายใน NGINX

RO: Erori HTTP aleatoare 520 NGINX / Cloudflare atunci când HTTP2 este activat în NGINX

RU: NGINX / Cloudflare случайные 520 ошибок HTTP, когда HTTP2 включен в NGINX

VI: Lỗi HTTP 520 ngẫu nhiên NGINX / Cloudflare khi bật HTTP2 trong NGINX

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