Nginx reverse proxy for requesting HTTP backend on HTTPS frontend - ssl

Question

I've been seeing a ton of info about reverse proxies and nginx but I'm a little lost on how to implement. I am running two separate EC2 instances (front and back end, with back end running pm2). I have SSL established on the front using LetsEncrypt, and it won't allow me to hit my backend because of Mixed Content. What should I do?
nginx.conf
server {
listen 80 default_server;
listen [::]:80 default_server;
server_name domain;
location / {}
return 301 https://$host$request_uri;
}
server {
listen 443 ssl;
listen [::]:443 ssl;
server_name localhost;
root /insert/root/here;
ssl_certificate "/path/to/cert";
ssl_certificate_key "/path/to/key";
ssl_session_cache shared:SSL:1m;
ssl_session_timeout 10m;
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_ciphers HIGH:SEED:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!RSAPSK:!aDH:!aECDH:!EDH-DSS-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA:!SRP;
ssl_prefer_server_ciphers on;
include /etc/nginx/default.d/*.conf;
location / {
}
error_page 404 /404.html;
location = /40x.html {
}
error_page 500 502 503 504 /50x.html;
location = /50x.html {
}
}

Answer 1

It looks like browser complains at your html content because it has hard-coded "http://" references to external resources, like javascript, fonts etc.
It does not mean that it can't reach backend due to this "mixed-content" issue.
I see no proxy_pass (or fastcgi_pass) directives in your config (which should pass requests to your upstream backend server) so probably that is an real reason why you can't reach your backend.
Your configuration should look like this:
server {
listen 443 ssl;
root /here/are/your/static/files/; # here you can place static html, css, js etc files from your backend to offload backend from serving static files - nginx will take care of them.
...
location / {
#this means that nginx will forward requests to backend server in case request does not match local static file.
try_files $uri $uri/ #backend;
}
location #backend {
#....
proxy_pass http://backend-server-ip-address:backend-port
}
}