Common Built-in Variables in the Nginx HTTP Module

Server Related

• $server_addr: Server address
• $server_name: Virtual host name (configured by the server_name directive)
• $server_port: Server port
• $document_root: Path configured by the root or alias command, which may be a symbolic link.
• $realpath_root: The actual path corresponding to the current request, absolute path.
• $request_filename: The file path of the current request, derived from the configuration of root or alias
• $host: The value from the Host header if present, otherwise the server_name (from nginx configuration)
• $hostname: Hostname of the server running nginx
• $nginx_version: Version of nginx
• $pid: Worker process ID
• $limit_rate: Value set by the limit_rate directive.

Example of variable usage for logging:

http {
 log_format about_server_log 'server_addr: $server_addr, server_name: $server_name, server_port: $server_port\n'
        'document_root: $document_root, realpath_root: $realpath_root, request_filename: $request_filename\n'
        'host: $host, hostname: $hostname, nginx_version: $nginx_version\n'
        'pid: $pid, limit_rate: $limit_rate';
 server {
  listen 80;
  server_name localhost;
  access_log logs/server.log about_server_log;

        location / {
            root   /var/www/html;
            index  index.html index.htm;
        }

  location /api/ {
   proxy_pass http://localhost:8009/api/;
   limit_rate 100k;
  }
 }
}

When requesting<span>http://xxx.xxx.xxx.xxx/5.jpg</span>, the value of $document_root is the path configured by the root directive, which is a symbolic link, while the value of $realpath_root is the actual physical path. When requesting<span>http://xxx.xxx.xxx.xxx/api/student/11</span>, the response comes from the proxy service, and the value of $request_filename is derived from the combination of the root configuration and$uri:

Client Related

• $binary_remote_addr: Binary representation of the client IP
• $remote_addr: Client IP
• $remote_port: Client port
• $remote_user: Username during HTTP Basic authentication
• $request: HTTP request, including method, URI, protocol, and version
• $request_method: Request method
• $request_uri: Complete URI
• $request_completion: Value is OK when the request is complete, otherwise an empty string
• $args or $query_string: Request parameters
• $arg_name: Value of the name parameter in the request
• $is_args: If there are request parameters, the value is ?, otherwise an empty string
• $scheme: Request protocol, http or https
• $https: Connection protocol, if https, the value is on, otherwise an empty string
• $http_host: Value of the Host header in the request
• $http_name: Value of the name header in the request
• $content_length: Content-Length in the request header
• $content_type: Content-Type in the request header
• $cookie_name: Value of the cookie with key name, name can also be other names
• $document_uri: This is$uri
• $server_protocol: HTTP protocol version

Example for if condition:

server {
 listen 80;
 server_name localhost;

 location /api/ {
  # Pass the username from HTTP Basic authentication to the upstream service
  proxy_set_header X-User $remote_user;

 # Check the request method
 if ($request_method != "GET") {
   return 405 "method not allowed";
  }

# Check the Content-Type type that can be handled
 if ($content_type != "application/json") {
   return 415 "Unsupported Media Type";
  } 
  proxy_pass http://localhost:8009/api/;
 } 
}

server {
 listen 81;
 server_name localhost;

 location / {
  # Redirect HTTP requests to HTTPS:
  if ($scheme = "http") {
   return 301 https://$host:443$request_uri;
  }

  ... 
 } 
}

Response Related

• $status: Response status code
• $sent_http_name: Name value in the response header
• $body_bytes_sent: Number of bytes sent in the response body
• $bytes_sent: Number of bytes sent in the response

Proxy Related

• $upstream_addr: IP and port of the upstream server
• $upstream_status: Response status code from the upstream server
• $upstream_response_time: Response time from the upstream service
• $proxy_host: Hostname and port of the target server in the proxy_pass directive
• $proxy_port: Port of the target server in the proxy_pass directive