In nginx's configuration, could "if (!-f $request_filename) {" cause a performance hit on virtual machines?

Question

If nginx is configured as a reverse proxy, could the following bit of configuration (counter-intuitively) cause a performance hit?

    if (!-f $request_filename) {
        proxy_pass http://app_server;
        break;
    }

This checks if a file exists, then serves it and finishes the request. However, this may cause some I/O to happen. If that file system is slow, might it be possible that forwarding the request to the proxied service ends up being faster?

Answer 1

Just like @mlbright said, if is bad, try to avoid it as much as you can, a good equivalent for the case you want to handle would be

location /whatever {
    try_files $uri @app_server;
}
location @app_server {
    proxy_pass http://app_server;
}