gistfile1.txt

server {
  listen 443;
  server_name customerold.ourplatform.net;
  ...
  
  location / {
    proxy_set_header Host customer.ourplatform.net;
    proxy_pass http://upstream_application;
    proxy_redirect http://customer.ourplatform.net https://customerold.ourplatform.net;
  }
}

server {
  listen 443;
  server_name customer.ourplatform.net;
  ...
  
  location / {
    proxy_set_header Host customernew.ourplatform.net;
    proxy_pass http://upstream_application;
    proxy_redirect http://customernew.ourplatform.net https://customer.ourplatform.net;
  }
}

gistfile2.txt

  location ~ ^/batches/([^/]+)/customer$ {
    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_pass http://quartermaster_application/batches/$1/customernew$is_args$args;
    proxy_redirect http:// https://;
    proxy_read_timeout 500;
  }