NGINX on AWS EC2 to forward HTTPS to HTTP://localhost

I have some dockers containers deployed on AWS EC2, that listens on http. My idea is using nginx as reverse proxy, to pass traffic from https, to http://localhost.

Each container listens on a specific http port. The EC2 instance will accept traffic just on http:80 and http:443 and I will use subdomain to chose the right port. So I should have:

https://backend.my_ec2instance.com --> http://localhost:4000
https://frontend.my_ec2instance.com --> http://localhost:5000

I'v got my free TSL certificate from Let's Encrypt (it's just on file containing public and private keys), and put it in

/etc/nginx/ssl/letsencrypt.pem

Then I have configured nginx in this way

sudo nano /etc/nginx/sites-enabled/custom.conf

and wrote

server {
       listen 443 ssl;
       server_name backend.my_ec2instance;
       # Certificate
       ssl_certificate letsencrypt.pem;

       # Private Key
       ssl_certificate_key letsencrypt.pem;

       # Forward
       location / {
               proxy_pass http://localhost:4000;
               }
}
server {
       listen 443 ssl;
       server_name frontend.my_ec2instance;
       # Certificate
       ssl_certificate letsencrypt.pem;

       # Private Key
       ssl_certificate_key letsencrypt.pem;

       # Forward
       location / {
               proxy_pass http://localhost:5000;
               }
}

then

sudo ln -s /etc/nginx/sites-available/custom.conf /etc/nginx/sites-enbled/

Anyway, if I open my browser on https://backend.my_ec2instance it's not reachable. http://localhost:80 instead correctly shows the nginx page.