C613-16088-00 REV A
www.alliedtelesis.com
How To|
Introduction
In many Server Hosting environments, two requirements are important: maximising
throughput availability to each service, and minimising service downtime. This How To Note
contributes towards both these aims.
The Note is split into two parts. The first part illustrates both redundancy of servers and
redundancy of the load balancers themselves. The second part provides an optional
extension that enables you to control server selection without losing redundancy. This is
helpful when you prefer to have customers access a certain server, instead of balancing that
traffic. However, if that server fails, the customers need to use the alternate server instead.
The examples
The network configuration for these examples is shown in the following figure.
The Note’s first example illustrates how to load balance web services, and includes:
• Load balancing of incoming web traffic to maximise throughput to web servers. It also
provides redundancy if a web server goes down.
• Redundancy between two load balancing routers. In the unlikely event of a router going
down, a backup router takes over as master and continues the load balancing work for
incoming web connections. Load balancer redundancy and VRRP ensure that clients and
servers access the same public and private addresses no matter which router is the master.
• A firewall to secure the LAN against attack. The firewall configuration changes
automatically if the backup router takes over the load balancing role.
Web/SFTP server 1
192.168.1.1
Web/SFTP server 2
192.168.1.2
private address
192.168.1.201
private
VLAN 3
with VRRP
virtual
address
192.168.1.202
public
VLAN 2
private address
192.168.1.200
public address
172.214.1.3
public address
172.214.1.4
redundancy
management
VLAN 4
192.168.2.2
redundant
load balancer
virtual address
172.214.1.2
Load Balancer 1
Load Balancer 2
client
redundancy
management
VLAN 4
192.168.2.1
public side private side
lb-redundancy.eps
Configure Load Balancer Redundancy on Allied Telesis
Routers and Switches
Configure Load Balancer Redundancy on Allied Telesis Routers and Switches 2
The Note’s second example extends the first example by showing how to control server
selection for SFTP (Secure File Transfer Protocol) traffic, while still providing server
redundancy if the preferred server fails.
For simplicity, these examples provide load balancing between two servers. You can easily
expand the examples by adding more servers.
What information will you find in this document?
As outlined above, the Note first describes basic load balancer redundancy. To configure
this, do all the following steps:
• "Configure Load Balancer 1" on page 3
• "Configure Load Balancer 2" on page 7
• "Create the Scripts" on page 9
Then the Note describes the optional extensions that let you control server selection. To
configure this, make all the following additions to the basic configuration:
• "Configure Load Balancing: Extra Commands" on page 10
• "Configure the Triggers: Extra Commands" on page 11
• "Modify the Scripts" on page 11
• "Create New Scripts" on page 12
Finally, the Note gives the complete extended configuration so you can verify your
configuration. Also, you may find it easier to copy this configuration to your router instead of
using the step-by-step configuration.
• "Commands: Load Balancer 1" on page 13
• "Commands: Load Balancer 2" on page 14
• "File: master.scp" on page 15
• "File: slave.scp" on page 15
• "File: sftp1down.scp" on page 15
• "File: sftp1up.scp" on page 15
Which products and software version does it apply to?
We created this configuration using AR440S routers and Software Version 275-05. However,
the configuration applies to the following products:
• AR44xS and AR450S Series routers
• AR750S, AR7x5 routers
• Rapier i Series switches
• AT-8800 Series switches
• AT-9800 Series switches
It requires software version 275-05 or later (except version 276-01, which lacks the
necessary trigger functionality).