Active/Standby Clustering

Installation

1. Install the VRRP module using your system's package manager on both instances of HAProxy Enterprise that will participate in your load balancer cluster:

   • apt Debian/Ubuntu
   • yum CentOS/RedHat/etc

   $ # On Debian/Ubuntu
   $ sudo apt-get install hapee-1.6r1-vrrp

   $ # On CentOS/RedHat/Oracle
   $ sudo yum install hapee-1.6r1-vrrp

2. On the instance that will serve as your active load balancer, edit the file /etc/hapee-1.6/hapee-vrrp.cfg. It looks like this:

   # Check for the presence of the SSH daemon. That way, if SSH dies, we prefer
   # the other node which remains remotely manageable.
   
   vrrp_script chk_sshd {
           script "pkill -0 sshd"          # pkill -0 is cheaper than pidof
           interval 5                      # check every 5 seconds
           weight -4                       # remove 4 points of prio if missing
           fall 2                          # check twice before setting down
           rise 1                          # check once before setting up
   }
   
   # Check for the presence of the load balancer daemon (hapee-lb) itself. The
   # weight is higher than for SSHD, because if one node only has SSHD and the
   # other one only has the LB running, we prefer the LB.
   
   vrrp_script chk_lb {
           script "pkill -0 hapee-lb"      # pkill -0 is cheaper than pidof
           interval 1                      # check every second
           weight 6                        # add 6 points of prio if present
           fall 2                          # check twice before setting down
           rise 1                          # check once before setting up
   }
   
   # This is an example of how it would be possible to check if the LB sees some
   # operational servers, and to use the result to decide to be primary or backup.
   # The "/are-you-ok" url should be referenced as a "monitor-uri" in hapee-lb,
   # and this vrrp_script should be referenced in the "track_script" block of the
   # concerned VRRP instances.
   
   vrrp_script chk_servers {
           script "echo 'GET /are-you-ok' | nc 127.1 8080 | grep -q '200 OK'"
           interval 2                      # check every 2 seconds
           weight 2                        # add 2 points of prio if OK
           fall 2                          # check twice before setting down
           rise 2                          # check twice before setting up
   }
   
   vrrp_instance vrrp_1 {
           interface eth0                  # or bond0 or whatever prod interface
           state MASTER                    # try to be primary (MASTER) without waiting
           virtual_router_id 51            # use a distinct value for each instance
           priority 101                    # 101 on primary, 100 on backup
           virtual_ipaddress_excluded {
                   55.55.55.55             # your shared service IP address(es)
           }
           track_interface {
                   eth0 weight -2          # interfaces to monitor
                   # eth1 weight -2
           }
           track_script {
                   chk_sshd
                   chk_lb
           }
   }

   In the vrrp_instance section, change the interface value from eth0 to the name of a network interface that receives traffic on the server. This is the same interface that you bind HAProxy Enterprise's frontend to. For example, if traffic reaches the load balancer using interface enp0s8, then set this line to interface enp0s8. Also, reference the same name in the track_interface block.

   Next, change the IP address listed in the virtual_ipaddress_excluded block to the virtual IP address you'd like to assign to this interface. HAProxy Enterprise will bind to this address to receive traffic. If needed, add more IP addresses here, each on its own line. The new address(es) should fall within the interface's IP subnet, but should not be assigned to any server already.

   The following snippet demonstrates these changes:

   vrrp_instance vrrp_1 {
           interface enp0s8                # Change network interface name
           state MASTER
           virtual_router_id 51
           priority 101
           virtual_ipaddress_excluded {
                   192.168.50.10           # NEW IP address
           }
           track_interface {
                   enp0s8 weight -2        # Change network interface name
           }
           track_script {
                   chk_sshd
                   chk_lb
           }
   }

3. Start the hapee-extras-vrrp service:

   $ sudo systemctl start hapee-extras-vrrp
   $ sudo systemctl enable hapee-extras-vrrp

4. Allow the server to bind to the virtual IP address.

   Edit the file /etc/sysctl.conf and add the net.ipv4_ip_nonlocal_bind=1 directive, which allows the server to accept connections for IP addresses that are not bound to any of its interfaces, enabling the use of a floating, virtual IP.

   net.ipv4.ip_nonlocal_bind=1

   Then reboot the server.

5. Configure your bind line in the HAProxy Enterprise configuration to use the virtual IP address.

   frontend myfrontend
     mode http
     bind 192.168.50.10:80
     default_backend web_servers

6. On your backup load balancer, the VRRP configuraton must be almost exactly the same. Edit the VRRP configuration file and the HAProxy Enterprise configuration in the same way, except:

   • change the priority field in the vrrp_instance block to have a lower number than the active instance; The load balancer with the highest priority is promoted to be the active instance. For example, if the priority on the active instance is 101, then set the backup instance's priority to 100.

   • change state to BACKUP.

   vrrp_instance vrrp_1 {
           interface enp0s8
           state BACKUP
           virtual_router_id 51
           priority 100                    # A lower priority value than the primary
           virtual_ipaddress_excluded {
                   192.168.50.10           # Same IP address as on primary
           }
           track_interface {
                   enp0s8 weight -2
           }
           track_script {
                   chk_sshd
                   chk_lb
           }
   }

Failover triggers

The following events can trigger a failover:

• The active instance lowers its weight below one of the backup instances due to a failed health check.

• A backup instance is reconfigured with a weight larger than the current active instance.

• The active instance stops emitting its heartbeat packet to the cluster.

vrrp_script chk_sshd {
  script "pkill -0 sshd"          # pkill -0 is cheaper than pidof
  interval 5                      # check every 5 seconds
  weight -4                       # remove 4 points of prio if missing
  fall 2                          # check twice before setting down
  rise 1                          # check once before setting up
}

vrrp_script chk_lb {
        script "pkill -0 hapee-lb"      # pkill -0 is cheaper than pidof
        interval 1                      # check every second
        weight 6                        # add 6 points of prio if present
        fall 2                          # check twice before setting down
        rise 1                          # check once before setting up
}

VRRP instance

The following fields define a vrrp_instance block: