I have 5 webservers behind Load balancer and we have a client server at other end. Client has white listed my 5 webserver public ip so that my webservers will post a file to the client server. Here the problem is my webservers is going to increase and i cannot always ask client to make my new webserver ip's white list. So i would like to make my infra this way, my webservers will post data to the client server routing from a single server. Like assume that web-1 is main server and the remaining 4 web servers will post data to client server routing through main web-1.

I was told that this can be achieved by doing IP Tunneling. But i have no idea how to do that. Would be great for any kind of help.