Load balancer as proxy or redirector

Question

The current situation: I have written an c# application server, which communicate with some applications (Computer/Smartphone/Web). Now I have the problem, that the application server has to deal with a lot of requests and it is going to be very slow.

My idea was to change the application server to work in a software cluster. To select the correct application server I want to write a load-balancer who choose the application server with the lowest workload.

My problem is, that I don't know how to write the load-balancer. Should the load-balancer work as a proxy, so that all the traffic goes through the load-balancer or should the load-balancer redirect to the application server and the application communicate directly with the application server.

Answer 1

Actually there are off-the-shelf products which do exactly what you're looking for, one of the most established ones is HAProxy that acts as a HTTP/TCP Load Balancer/ HA proxy, it can select appropriate server based on previous client requests (e.g. by cookie -insertion, it supports other methods), which I believe does exactly what you need.

back to the question,

Should the load balancer work as a proxy, so that all the traffic goes through the load balancer or should the load balancer redirect to the application server

Proxy implementation is a normal route to take, and Redirecting is not such a good idea and cause some disturbing issues on client-side specially browsers (e.g. bookmarks won't work as intended) and I would say it wouldn't have much gain over using proxy (aside from removing load balancer node if balancing is going to be done on client-side)

that i don't know how to write the load balancer

Short answer is you don't need to write your own, as I said before there are well established products in this area, however if you want to write your own HAProxy Architecture manual and Writing a load balancer proxy from ground up would be good start.

Answer 2

Answering in two parts:

1. You need a Proxy functionality, and not a redirect or a router function. A redirect would reveal the IP/URL for your backend server pool to the client, which you certainly do not want. The clients could always bypass your LB once they know the backend IPs. Thus, all the traffic must flow through the proxy.

2. I would not recommend entering the realm of writing a LB. Its a pretty specialized function, and there are many free/commercial baked products that can be deployed for this. You might choose one of HAProxy, Appache HTTPD, Microsoft NLB, NginX. Each one offers a configuration choice of many load balancing algorithms, that you may want to use.