You can configure your web server running on port 80 to simply issue a redirect to 443/HTTPS, before it even hits Moodle.
Apache: https://wiki.apache.org/httpd/RedirectSSL
Nginx: https://www.digitalocean.com/community/questions/http-https-redirect-positive-ssl-on-nginx
Suggest also using HTTP Strict Transport Security/HSTS, to prevent protocol-downgrade attacks.
Apache/Nginx: https://raymii.org/s/tutorials/HTTP_Strict_Transport_Security_for_Apache_NGINX_and_Lighttpd.html