How do I diagnose a long Initial Connection to webpage hosted in AWS with Nginx/ELB/ECS

Question

I have a React web page that uses the Razzle framework for SSR, containerised and deployed into ECS along with an Nginx container. I use Route 53 for DNS, which routes the record to an ELB, then to the target group where my container resides.

If I clear all browsing data and go to the site, it takes over a minute to establish an "Initial Connection" and everything else looks quick. Subsequent loads of the page do not take long at all.

I have no idea where to start to diagnose the issue, does anyone have an idea where I should look?

Here is my Nginx configuration file

server {
  listen 80;
  listen [::]:80;

  if ($http_x_forwarded_proto = 'http'){
    return 301 https://$host$request_uri;
  }

  location / {
    proxy_pass http://0.0.0.0:3000;
    proxy_http_version 1.1;
    proxy_redirect     off;
    proxy_set_header   Upgrade $http_upgrade;
    proxy_set_header   Connection "Upgrade";
    proxy_set_header   Host $host;
    proxy_set_header   X-Real-IP $remote_addr;
    proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header   X-Forwarded-Host $server_name;
  }
}

server {
  server_name www.<domain>.com;
  return 301 $scheme://<domain>.com$request_uri;
}

Answer 1

I found my issues was due to my ELB configuration where I had two private subnets associated instead of public subnets. After creating a public subnet in each availability zone and associating it with the ELB the initial connection time became negligible.