Specifications

Pools
BIG-IP® Reference Guide 4-21
be confined to that group. If the number of available nodes in the highest
priority group goes below the minimum number, the BIG-IP also distributes
traffic to the next higher priority group, and so on.
The configuration shown in Figure 4.6 has three priority groups, 3, 2, and 1.
Connections are first distributed to all nodes with priority 3. If fewer than
two priority 3 nodes are available, traffic is directed to the priority 2 nodes
as well. If both the priority 3 group and the priority 2 group have fewer than
two nodes available, traffic is directed to the priority 1 group as well. The
BIG-IP continuously monitors the higher priority groups, and each time a
higher priority group once again has the minimum number of available
nodes, the BIG-IP again limits traffic to that group.
If you set the load balancing mode to Ratio (as opposed to Ratio Member),
you must define the ratio settings for each node address.
Persistence
If you are setting up an e-commerce or other type of transaction-oriented
site, you may need to configure persistence on the BIG-IP. Persistence is
one of the pool attributes listed in Table 4.1.
Whether you need to configure persistence or not simply depends on how
you store client-specific information, such as items in a shopping cart, or
airline ticket reservations. For example, you may store the airline ticket
reservation information in a back-end database that all nodes can access, or
on the specific node to which the client originally connected, or in a cookie
on the client’s machine.
If you store client-specific information on specific nodes, you need to
configure persistence. When you turn on persistence, returning clients can
bypass load balancing and instead can go to the node where they last
connected in order to get to their saved information.
pool my_pool {
lb_mode fastest
min_active_members 2
member 10.12.10.1:80 priority 3
member 10.12.10.2:80 priority 3
member 10.12.10.3:80 priority 3
member 10.12.10.4:80 priority 2
member 10.12.10.5:80 priority 2
member 10.12.10.6:80 priority 2
member 10.12.10.7:80 priority 1
member 10.12.10.8:80 priority 1
member 10.12.10.9:80 priority 1
}
Figure 4.6 Sample pool configuration for priority based member activation