Your First Load Balancer

Now that HAProxy is installed, it's time to configure your first load balancer.

Before we dive in, let’s review the lab environment you’ll be working in.

In this lesson—and most of the ones that follow—you’ll interact with several machines, each with a specific role:

• dev-machine – Your "local machine" used to do testing (i.e. send requests to HAProxy).
• loadbalancer – The machine where HAProxy will be configured.
• backends – Servers acting as backend services, listening to HTTP and SSH traffic on ports 80 and 22.

Network topology

To reflect a real-world setup, dev-machine cannot access the backends directly. All traffic must go through the load balancer.

Go to the loadbalancer tab and create the following configuration file:

listen my_lb
  bind :80

  server backend-01 backend-01:80
  server backend-02 backend-02:80
  server backend-03 backend-03:80

Restart the service for the changes to take effect:

sudo systemctl restart haproxy

Switch to the dev-machine tab and try sending requests to the load balancer:

while true; do curl http://loadbalancer; sleep 2; done

You should see something like this:

Hello from backend-01!
Hello from backend-02!
Hello from backend-03!
Hello from backend-01!
Hello from backend-02!
Hello from backend-03!

🎉 Congratulations!

You've successfully configured your first load balancer using HAProxy.

Let’s go through the configuration options one by one.

The listen block tells HAProxy to listen on specified IP addresses and ports, and to forward incoming connections to a defined set of backends.

To specify which IP addresses and ports HAProxy should listen on, use the bind directive.

In this example, bind :80 tells HAProxy to listen on port 80 across all available network interfaces.

Here are a few other ways you can use the bind directive:

Finally, the server directive tells HAProxy where to forward incoming traffic.

In this example, three backend servers are defined. HAProxy will forward each request to one of them, selected at random.

New configuration options introduced in this lesson:

• listen block
• bind directive
• server directive