Codeigniter on Nginx generates https action for form, but not Apache
Assuming you are using the automatic site_url detection, Codeigniter's own http/https detection relies on the $_SERVER['HTTPS'] value to be off if it is in fact set to something, to generate the http for the base_url.
Check your default fastcgi_params (usually /etc/nginx/fastcgi_params), maybe it sets it to an empty string or something other than "off", also you can force this from nginx config with this to be "off":
fastcgi_param HTTPS off;If you are using one server block for both the http and https connection inside the nginx's config file, you can use a mapping to create the value you need based on the $scheme variable:
# somewhere inside http { ... }map $scheme $php_https { default off; https on; }And reference it in the fastcgi_param:
fastcgi_param HTTPS $php_https;
Check your config.php on the Nginx box vs the Apache box. site_url returns what you have specified in your $config['base_url'] entry in config.php