ServerIron ADX Server Load Balancing Guide

Release 12.0.00

June 15, 2009

PBSLB Pool Failsafe Group

This feature allows a ServerIron ADX to direct traffic away from a given server pool to a "default pool" in situations where the servers in the server pool become unavailable.

Overview of PBSLB Pool Failsafe Group

When PBSLB is used to filter traffic based on source IP address, a ServerIron ADX looks up a group id for the client to forward the incoming request to. If all the servers in the group fail, the ServerIron ADX sends a TCP reset to the client, causing the request to fail. This feature allows you to configure a failsafe group, which will be used to forward traffic, in case the group designated for a client source-ip address fails. The following section outlines the behavior of this feature in two scenarios.

•	“For IPs present in the PBSLB list:”

•	“For IPs not present in the PBSLB list:”

For IPs present in the PBSLB list:

•	If the group-id is 0 (deny group), the traffic is denied (RST in case of tcp and drop in case of udp).

•	If the group-id is not 0, and if servers are healthy and max-conn limit is not reached, traffic is load balanced among servers as per predictor.

•	If all servers of the group are in a failed state or the max-conn limit is reached, traffic is load balanced among "failsafe" group servers.

•	If all of the servers of the "failsafe" group are in a failed state or the max-conn limit is reached, traffic is denied (RST in case of TCP and drop in case of UDP).

For IPs not present in the PBSLB list:

•	If the default-group-id is not configured or it is configured as 0(deny group), traffic is denied.

•	If the default-group-id is configured, traffic is load balanced among default-group servers as per predictor.

•	If all of the servers of the default-group are in a failed state or themax-conn limit is reached on all servers, the traffic is load balanced among "failsafe" group servers.

•	If all of the servers of the failsafe group are in a failed state or the max-conn limit is reached, the traffic is denied.

Command Line Interface

There are two steps to enable this feature.

1.	Create pbslb failsafe group-id

2.	Assign real server ports to a

3.	failsafe group

4.	Enable pbslb on a VIP port

Create a PBSLB failsafe group

To create a PBSLB failsafe group, enter a command such as the following:

ServerIron(config)# server pbslb failsafe-group-id 2

Syntax: [no] server pbslb failsafe-group-id <group-id>

Assign Real Server Ports to a Failsafe Group

A failsafe group can contain one or more real servers. If there is more than one real server in a failsafe group, requests are load balanced across all the servers in the group. To assign real servers to the failsafe group, enter commands such as the following:

ServerIron(config)# server real-name rs1 207.95.7.1
ServerIron(config-rs-rs1)# port http group-id 2 2
ServerIron(config-rs-rs1)# exit

Enable PBSLB on a VIP Port

To enable PBSLB on a vip port,enter commands such as the following:

ServerIron(config)# server virtual-name-or-ip mysite 209.157.22.63

ServerIron(config-vs-mysite)# port http

ServerIron(config-vs-mysite)# port http sw-l4-pbslb

ServerIron(config-vs-mysite)# bind http rs1 http

Show Commmands

To view the number of requests forwarded to the failsafe server group, enter the following command:

ServerIron# show pblsb failsafe

Syntax: show pbslb failsafe

To clear PBSLB fail-safe counter, enter the following command:

ServerIron# clear pbslb failsafe

Syntax: clear pbslb failsafe