Lets say you are hosting www.example.com with an NGINX front-end and you want to re-direct http://example.com and https://example.com to http://www.example.com. Here is the NGINX config to do that

server {
listen 80;
server_name example.com;
return 302 https://www.example.com$request_uri;
}

server {
listen 443;
server_name example.com;
return 302 https://www.example.com$request_uri;
}

server {
listen 443 default_server ssl;
client_max_body_size 4M;

...

}