Initial configuration
Your initial configuration file contains the following structure:
defaults mode http timeout client 10s timeout connect 5s timeout server 10s timeout http-request 10s frontend myfrontend bind 127.0.0.1:80
This example includes:
defaults
section, which defines settings that are shared across all sections that follow. It sets (These are just good safety measures that will help avoid common problems.):- timeouts for how long HAProxy should wait for a client to send data (
timeout client
), - how long to wait when trying to connect to a backend server (
timeout connect
), - how long to wait for the server to send back data (
timeout server
), - how long to wait for the client to send a complete HTTP request (
timeout http-request
). mode
sets how HAProxy treats requests. It can be either http or tcp, with the former used when working with HTTP web applications. In this mode, HAProxy is able to inspect metadata of an HTTP request, such as headers, cookies, and the URL path, when deciding how to route the request.
- timeouts for how long HAProxy should wait for a client to send data (
The load balancer is now listening on the localhost address, 127.0.0.1, at port 80. If you make a request using curl
, you’ll get back a response:
$ curl 127.0.0.1:80 <html><body><h1>503 Service Unavailable</h1> No server is available to handle this request. </body></html>
Granted, there’s no reply from a server because we haven’t configured any servers yet. Nevertheless, you can see that HAProxy is functional.
Add a backend server
In HAProxy, a frontend receives traffic before dispatching it to a backend, which is a pool of web or application servers. One of the servers in the backend will receive the request, form a response, and then send the response back through HAProxy to the client.
In your HAProxy configuration, below the frontend
section, add a backend
section that contains a single server. Also, add a default_backend
line to your frontend that points to this new backend. Your file now looks like this:
defaults mode http timeout client 10s timeout connect 5s timeout server 10s timeout http-request 10s frontend myfrontend bind 127.0.0.1:80 default_backend myservers backend myservers server server1 127.0.0.1:8000
You can also add multiple backends:
defaults mode http timeout client 10s timeout connect 5s timeout server 10s timeout http-request 10s frontend myfrontend bind 127.0.0.1:80 default_backend myservers backend myservers server server1 127.0.0.1:8000 server server2 127.0.0.1:8001 server server3 127.0.0.1:8002
With each new request that you make to port 80, HAProxy receives it and selects a server to handle it. HAProxy rotates through the list of servers, relaying the next request to the next server in line. You are now balancing the load across these servers.
Resources
https://www.haproxy.com/blog/haproxy-configuration-basics-load-balance-your-servers