Nginx always not resolving path using $server_name with try_files

Question

I have the following location configuration as part of a reverse proxy server:

error_page 503 502 @down;
location @down {
  try_files /error/test/$server_name.html /error/test/generic.html;
  internal;
}
location /error/ {
  root /usr/share/nginx/html/;
  internal;
}

For a server block with server_name of events.example.com, I would expect /usr/share/nginx/html/error/test/events.example.com.html to be served if it exists. Otherwise Nginx should serve /usr/share/nginx/html/error/test/generic.html.

Nginx is always displaying the generic.html page, even when the more specific page exists. I thought that it might be that the variable wasn't being evaluated, so I created a file called $server_name.html in the error directory. The problem still persisted. If I change the try_files line to

index /error/test/$server_name.html

the configuration works as expected.

How can I have Nginx resolve a file based on the $server_name variable and fallback to a generic file if the first file does not exist?

Answer 1

Your root statement is not in scope when the try_files statement is encountered. So nginx cannot determine the correct path to the file.

Also, try_files will process the file terms within the same location, so you could combine both locations into a single named location (assuming that location /error/ { ... } is not required elsewhere).

For example:

error_page 503 502 @down;
location @down {
  root /usr/share/nginx/html/;
  try_files /error/test/$server_name.html /error/test/generic.html =404;
}

Add the =404 so that the second parameter is treated as a file parameter and not a URI parameter. See this document for more.