connect() failed (110: Connection timed out) while connecting to upstream - nginx

Question

I have configured nginx setup like below
Nginx running as front end reverse proxy and routing live traffic to couple of upstream servers onprem and aws (Refer nginx site conf below). Here we trying to mirror the original On-Prem hosted application traffic to AWS hosted application which we using it as pre-production testing before completely migrate application to AWS cloud.
We noticed below things,
All original live traffic routed to onprem upstream server which is running on localhost:10200
We see few request failed with connection timeout while mirroring to aws upstream server which is running in AWS cloud
I am getting below error in nginx error log
connect() failed (110: Connection timed out) while connecting to
upstream
upstream onprem {
server localhost:10200;
keepalive 1024;
}
upstream aws {
server <myserver-name>:443;
keepalive 1024;
}
server {
server_name _;
listen 80 default_server;
client_header_buffer_size 16k;
client_header_timeout 900s;
client_max_body_size 100M;
client_body_buffer_size 100M;
client_body_timeout 900s;
proxy_connect_timeout 200s;
proxy_send_timeout 1200s;
proxy_read_timeout 1200s;
send_timeout 1200s;
proxy_buffers 16 128k;
proxy_buffer_size 16k;
proxy_redirect off;
proxy_busy_buffers_size 256k;
port_in_redirect off;
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_http_version 1.1;
proxy_set_header Connection "";
location / {
mirror /mirror;
proxy_pass http://onprem;
}
location = /mirror {
add_header 'Access-Control-Allow-Origin' 'https://myserver-name';
add_header 'Access-Control-Allow-Credentials' 'true';
add_header 'Access-Control-Allow-Headers' 'Authorization,Accept,Origin,DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';
add_header 'Access-Control-Allow-Methods' 'GET,POST,OPTIONS,PUT,DELETE,PATCH';
internal;
set $delimiter "?";
if ($is_args) {
set $delimiter "&";
}
#log_subrequest on;
set $flag "${delimiter}useTest=true";
if ($request_method = 'OPTIONS') {
add_header 'Access-Control-Allow-Origin' 'https://myserver-name';
add_header 'Access-Control-Allow-Credentials' 'true';
add_header 'Access-Control-Allow-Headers' 'Authorization,Accept,Origin,DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';
add_header 'Access-Control-Allow-Methods' 'GET,POST,OPTIONS,PUT,DELETE,PATCH';
add_header 'Access-Control-Max-Age' 1728000;
add_header 'Content-Type' 'text/plain charset=UTF-8';
add_header 'Content-Length' 0;
return 204;
}
proxy_ssl_server_name on;
set $new_uri $request_uri;
if ($request_uri ~ "^/ingest(.*)$") {
set $new_uri /test$1;
}
proxy_pass https://aws$new_uri$flag;
}
}