Limit upload file size and redirect user to error page if limit exceeds

You should be able to do this using something like:

server {
  server_name example.com;

  client_max_body_size 10m; # or whatever size limit you want
  error_page 413 /custompage.html; # you can also use a named location here if you like
}

• http://nginx.org/en/docs/http/ngx_http_core_module.html#client_max_body_size
• http://nginx.org/en/docs/http/ngx_http_core_module.html#error_page

Don't forget to set post_max_size and upload_max_filesize to corresponding value in php.ini.