HaProxy description

HaProxy is a widely used Load Balancer that is available on almost every Linux distribution. You can install it on Ubuntu using the following bash command:

sudo apt install haproxy

Official website: http://www.haproxy.org/
Man Page: http://manpages.ubuntu.com/manpages/xenial/man1/haproxy.1.html

Sample Configurations

This section contains a few examples for configuring HaProxy. For production environments, please refer to the official haproxy.org documentation in order to be sure that the configuration is optimal for your solution

HaProxy for Web servers

This section contains example on how to configure HaProxy to load balance traffic between web servers. For quick setup, append the following code to /etc/haproxy/haproxy.cfg:

frontend http
  bind *:80
  mode http
  default_backend web-backend
 
backend web-backend
   balance roundrobin
   server httpd-01 10.10.20.21:80 check
   server httpd-02 10.10.20.22:80 check
   server httpd-03 10.10.20.23:80 check

More complex solutions might require SSL (HTTPS).

# code block for https required

For information regarding the Apache2 HTTPD web server, please visit the official server guide.

HaProxy for Galera Cluster

HaProxy can be used in association with Galera cluster in order to load balance traffic between the MariaDB/MySQL Nodes. If you want to run a quick setup, append the following code to /etc/haproxy/haproxy.cfg:

listen galera
        bind 127.0.0.1:3306
        balance leastconn
        mode tcp
        option tcpka
        option mysql-check user haproxy
        server mariadb-server1 10.10.10.11:3306 check weight 1
        server mariadb-server2 10.10.10.12:3306 check weight 1
        server mariadb-server3 10.10.10.13:3306 check weight 1

For the checks to work, you must create a haproxy user within the database:

CREATE USER 'haproxy'@'10.10.20.21';

This setup assumes that your database servers are part of network 10.10.10.0/24 and that the server where haproxy runs has the IP 10.10.20.21.
The bind address is 127.0.0.1:3306 since you will probably install this on the server where your Apache2 is running, and Apache2 will need to connect to the DB.

Using keepalived for high availability

In some cases you might need to always have a haproxy instace running, for production environments. If downtime is not accepted, please consider keepalived to shift the IP to another server in case your main servers goes down. Use the following command to install keepalived:

apt install keepalived

Let's assume that your haproxy configutation has the following IPs:

• haproxy-node-01: 10.10.30.11 on eth0
  haproxy-node-02: 10.10.30.12 on eth0
  

You will need a 3rd IP to shift between the two servers when one of them goes down. Let's assume the IP that will be always available is 10.10.30.50.

For such an example, the configuration for would be as follows bello:

On node haproxy-node-01, create /etc/keepalived/keepalived.conf and add the following to it:

global_defs {
   smtp_server localhost
   smtp_connect_timeout 30
}
 
vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 101
    priority 101
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        10.10.30.50
    }
}

On node haproxy-node-02, create /etc/keepalived/keepalived.conf and add the following to it:

global_defs {
   smtp_server localhost
   smtp_connect_timeout 30
}
 
vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 101
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        10.10.30.50
    }
}

As you can see, the two nodes have similar configutation. The big difference is the priority, which states that haproxy-node-01 will be active and that haproxy-node-02 will be standby. The lower priority on the 2nd node meands that the 2nd node will take 10.10.30.50 only when node-01 is down.

This configuration can be tested by running ip addr to check the IPs on each machines. With a running setup, node-02 will take the virtual IP when node-01 is down.