HAProxy Agent Check Example

This is a small program that demonstrates an agent health check for HAProxy. Written in Go, it checks the (Linux) system's CPU idle time. If that metric falls below 10, the string 50%\n is sent back to HAProxy, which sets the server's weight in the load balancer to half of what it was.

How to use it

1. Build the agent program with Go:

   GOOS=linux GOARCH=amd64 go build -v -o ./agent .

2. Copy the agent program to your webserver and run it:

   ./agent

Demo

1. Build and run the demo using Docker Compose:

   cd demo
   sudo docker-compose build
   sudo docker-compose up

   This hosts a website at http://localhost. You can see the HAProxy Stats page at http://localhost:8404.

2. To artifically increase CPU usage on the webserver, run the stress-ng command:

   sudo docker-compose exec webserver1 stress-ng --cpu 8 --timeout 20
   

3. Watch the HAProxy Stats page at http://localhost:8404/ to see the server's weight change.

   You can also change the action that HAProxy takes. For example, change the agent.go code so that it sets the server to up or down:

   c.Send("up\n")
   
   ...
   
   c.Send("down\n")