# HAProxy on a VDS: Load Balancing and Health Checks

> HAProxy on a VDS distributes traffic across servers — see how to install it, set up health checks, and choose roundrobin or leastconn balancing.

## What HAProxy is and when you need it on a VDS

HAProxy is a TCP/HTTP load balancer and proxy that distributes incoming requests across multiple backend servers. It sits in front of a pair of web servers, a PHP-FPM cluster, or several application instances so the setup survives the failure of one node and traffic gets spread evenly. HAProxy was built from the start specifically as a load balancer and can monitor backend health deeply — there is a separate article on [Nginx as a load balancer](https://www.zevshost.net/en/kb/nginx-load-balancer/) for a lighter option.

HAProxy is useful when a VDS, or several VDS instances, run more than one copy of an application and you need to decide where to route each request, as well as automatically remove failed servers from rotation.

## Installing HAProxy on Ubuntu and Debian

The HAProxy package is available in the standard repositories. Install it and check the version:

```
apt update
apt install haproxy -y
haproxy -v
```

The service registers with systemd right away. The main configuration file is located at `/etc/haproxy/haproxy.cfg`. Make a backup before any changes:

```
cp /etc/haproxy/haproxy.cfg /etc/haproxy/haproxy.cfg.bak
```

## Basic configuration: frontend and backend

HAProxy configuration is built from a `frontend` section (what to listen on) and a `backend` section (where to send traffic). A minimal working example for distributing HTTP traffic between two servers:

```
frontend http_front
    bind *:80
    default_backend http_back

backend http_back
    balance roundrobin
    server web1 10.0.0.11:80 check
    server web2 10.0.0.12:80 check
```

The `check` parameter at the end of the `server` line enables an availability check for that backend — without it HAProxy never finds out the server is down and keeps sending traffic to it.

## Backend health checks

By default, HAProxy checks the TCP connection to the backend's port every few seconds. For HTTP services, it is better to enable a check against a specific URL to tell an open port apart from an application that actually responds:

```
backend http_back
    option httpchk GET /health
    http-check expect status 200
    server web1 10.0.0.11:80 check inter 3000 fall 3 rise 2
    server web2 10.0.0.12:80 check inter 3000 fall 3 rise 2
```

The `inter 3000` parameter sets the check interval to 3000 milliseconds, `fall 3` is how many failed checks in a row remove a server from rotation, and `rise 2` is how many successful checks bring it back.

## Load balancing algorithms

The `balance` parameter in the backend section defines how requests are distributed. The main options:

| Algorithm | Working principle |
| --- | --- |
| roundrobin | Cycles through each server in turn |
| leastconn | Sends to the server with the fewest active connections |
| source | Hashes the client IP — the same client always reaches the same server |

For session-based applications without shared session storage, use `source` or `balance leastconn` with `stick-table` enabled, so a user does not lose their login when switching between backends.

## Checking the configuration, reloading, and monitoring

Before applying a new configuration, always check the syntax — an error in the file brings down the entire balancer and blocks traffic to all backends at once:

```
haproxy -c -f /etc/haproxy/haproxy.cfg
systemctl reload haproxy
```

Production checklist:

- Always validate the config with `haproxy -c` before `reload`.
- Point `httpchk` at a real application health endpoint, not just the site root.
- Open the balancer's port in the firewall — see the article on [configuring UFW on a VDS](https://www.zevshost.net/en/kb/ufw-firewall-vps/).
- Connect general server resource monitoring alongside HAProxy — see the article on [VDS resource monitoring](https://www.zevshost.net/en/kb/monitoring-vds/).
- Enable the HAProxy stats page (`stats enable`) on a separate port to see backend status in real time.

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Source: https://www.zevshost.net/en/kb/haproxy-nastroika/