Custom load balancing

Help!
1

Hi,

I am using HAProxy for load balancing my HTTP requests. I would like to know if there is any way to customize the selection of backend server based on the responses returned by each server. I have a servlet which can return the responses (number of clients connected to it). I would like to use this information and route the request to the backend server which has the lowest number.

My HAProxy configuration looks like:

listen http_front xx.xx.xx.xx:8080
  mode http
  option httpchk GET /servlet/IHealthCheckServlet
  server app1 xx.xx.xx.xx:8080 check port 8080
  server app2 xx.xx.xx.xx:8080 check port 8080
  server app3 xx.xx.xx.xx:8080 check port 8080

Can you help me in this regard.

2

Well you can just use the leastconn algorithm to do this, its just a single option:
https://cbonte.github.io/haproxy-dconv/1.7/configuration.html#4.2-balance

I suggest you work with existing load balancing algorithms haproxy provides. You have a lot of options and should be able to find what you require easily (as I said leastconn probably already satisfies your requirement).

Custom application controlled load balancing can be complicated and cumbersome - a delayed reaction to high load may actually have the opposite effect and self-DDoS your backend servers.

However, yes, with the appropriate load-balancing algorithm you can shift the load by adjusting server weights. You can do this via the admin socket, or better yet with auxiliary agent checks:

https://cbonte.github.io/haproxy-dconv/1.7/configuration.html#5.2-agent-check

You may even be able to intercept HTTP responses with LUA and set appropriated server weights.

3

@Sunil I’m searching for a solution like you.

I experienced “leastconn” often is not good enough, as also in our case the tcp connection count does not reflect the usage. In my case the number of clients is more important, too.

Did you find any suitable solution with HAProxy?

Do you have a working example configuration?