Does nginx fastcgi_pass support variables?

I would like to use dynamic host resolution with nginx and fastcgi_pass.

When fastcgi_pass $wphost:9000;

set to conf, nginx displays an error [error] 7#7: *1 wordpress.docker could not be resolved (3: Host not found),

but when i install fastcgi_pass wordpress.docker:9000;

it works except for the fact that after restarting wordpress nginx still points to the old ip.

server {
  listen [::]:80;
  include /etc/nginx/ssl/ssl.conf;

  server_name app.domain.*;

  root /var/www/html;
  index index.php index.html index.htm;

  resolver 172.17.42.1 valid=60s; 
  resolver_timeout 3s;

  location / {
    try_files $uri $uri/ /index.php?q=$uri&$args; ## First attempt to serve request as file, then as directory, then fall back to index.html
  }

  #error_page 404 /404.html;
  error_page 500 502 503 504 /50x.html;
  location = /50x.html {
    root /usr/share/nginx/html;
  }

  set $wphost wordpress.docker;  

  # pass the PHP s to FastCGI server listening on wordpress.docker
  location ~ \.php$ {
    client_max_body_size    25M;
    try_files               $uri =404;
    fastcgi_split_path_info ^(.+\.php)(/.+)$;
    fastcgi_pass            $wphost:9000;
    fastcgi_param           SCRIPT_FILENAME $document_root$fastcgi_script_name;
    fastcgi_param           SCRIPT_NAME $fastcgi_script_name;
    fastcgi_index           index.php;
    include                 fastcgi_params;
  }

  location ~* \.(jpg|jpeg|gif|png|css|js|ico|xml)$ {
    add_header        Pragma public;
    add_header        Cache-Control "public, must-revalidate, proxy-revalidate";
    access_log        off;
    log_not_found     off;
    expires           168h;
  }

  # deny access to . files, for security
  location ~ /\. {
        access_log    off;
        log_not_found off; 
        deny          all;
  }

}

      

        
        
        
      

    

I have a different virtual host configuration where I am using proxy_pass http://$hostname;

and in this setting everything works as expected and the node is found.

After doing various options, I'm wondering if the fastcgi_pass

variables support