After fresh installation nginx on Amazon Linux 2 (EC2) following commands,

$ amazon-linux-extras install nginx1
$ nginx -v
nginx version: nginx/1.22.0
$ cat /proc/version
Linux version 5.10.144-127.601.amzn2.x86_64 (mockbuild@ip-10-0-44-229) (gcc10-gcc (GCC) 10.3.1 20210422 (Red Hat 10.3.1-1), GNU ld version 2.35-21.amzn2.0.1) #1 SMP Thu Sep 29 01:11:59 UTC 2022

I'm confused about the behavior of upstream directive is not working as my expectation. I just want http://my-domain.com to pass all requests to http://1234-567-89-012-345.ngrok.io and returns results without domain changes.

Starting from the default config file /etc/nginx/nginx.conf, The followings are my tries.

(GET http://1234-567-89-012-345.ngrok.io/ping returns pong as text response)

Try 1

• Modification

  upstream devproxy {
      server 1234-567-89-012-345.ngrok.io;
  }
  
  server {
      listen 8081;
      listen [::]:8081;
      server_name devproxy_server;
  
      location / {
          proxy_pass http://devproxy;
      }
  }
  

• Expected: Navigate to http://1234-567-89-012-345.ngrok.io/ping on Google Chrome, and show text pong on the page.
• Actual: Navigate to http://1234-567-89-012-345.ngrok.io/ping, then redirect to https://devproxy/ping(literally, not an alias) with DNS_PROBE_FINISHED_NXDOMAIN. See the screenshot

Try 2

• Modification

  server {
      listen 8081;
      listen [::]:8081;
      server_name devproxy_server;
  
      location / {
          proxy_pass http://1234-567-89-012-345.ngrok.io;
      }
  }
  

• Expected: Navigate to http://1234-567-89-012-345.ngrok.io/ping on Google Chrome, and show text pong on the page.
• Actual: It works as I expected. See the screenshot

Am I missing something? Thanks a lot for your answers! :)