nginx "randomly" serves the wrong server

Question

I have an nginx server with several servers, basically the config file looks like this:

http {
    server {
        listen              [::]:80;
        listen              80;
        server_name         DOMAIN1.com www.DOMAIN1.com;

        location ~ \.php$ {
            // ...
            fastcgi_pass            unix:/run/php/DOMAIN1-php7.3-fpm.sock;
        }

        listen [::]:443 ssl http2 ipv6only=on; 
        listen 443 ssl http2; 
        ssl_certificate /etc/letsencrypt/live/DOMAIN1/fullchain.pem; 
        ssl_certificate_key /etc/letsencrypt/live/DOMAIN1/privkey.pem; 
        include /etc/letsencrypt/options-ssl-nginx.conf; 
        ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; 
    }

    server {
        listen              [::]:80;
        listen              80;
        server_name         DOMAIN2.com www.DOMAIN2.com;

        location ~ \.php$ {
            // ...
            fastcgi_pass            unix:/run/php/DOMAIN2-php7.3-fpm.sock;
        }

        listen [::]:443 ssl http2 ipv6only=on; 
        listen 443 ssl http2; 
        ssl_certificate /etc/letsencrypt/live/DOMAIN2/fullchain.pem; 
        ssl_certificate_key /etc/letsencrypt/live/DOMAIN2/privkey.pem; 
        include /etc/letsencrypt/options-ssl-nginx.conf; 
        ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; 
    }
}

When I open DOMAIN1.com the page usually loads. But when I refresh the page several times, I will eventually get the contents of DOMAIN2.com - the same happens on DOMAIN2.com

I have 10 domains in total, and there is no "default" domain; i.e. when a wrong site is served, it's always a different one.

I can actually observe a pattern: When I make a request to a domain it works. Then I open a different browser and load a different domain. Then I refresh the first browser it serves the domain that I just opened on the second browser.

Any idea how I could debug/fix this or what configuration actually triggers this behavior?

Did you test with setting one of the domains as the "default"? Do you then still get the same issues? — Tommiie, Mar 12 '19 at 11:03
This is how nginx load balancing like you did in your config works ... there is no `root`, no server block config for different sites, so you have the requests balanced. — bjoster, Mar 12 '19 at 13:37

Philipp · Answer 1 · 2019-03-12T23:07:17.960

For the record: It actually turns out, that this is no issue with nginx but with PHP.

I hadded the following line to all server blocks in nginx:

add_header X-Source-Server <DOMAIN>-$server_addr;

Here I can clearly see, that the correct nginx server block is chosen and it forwards the process correctly to the PHP FPM pool. However, the PHP pool picks the wrong Database/Docroot for some reason.

Actually, this question describes my problem:
FPM sometimes serving from wrong pool -> Possibly it's a problem caused by opcache or similar.

Following the advice I found in this blog post I could solve the issue ("why multiple PHP-FPM masters are better"). After creating a new PHP-FPM master for each domain everything is stable

nginx "randomly" serves the wrong server

1 Answers1