Installation guide

7-11
Device Manager Guide, Cisco ACE 4700 Series Application Control Engine Appliance
OL-26645-02
Chapter 7 Configuring Stickiness
Configuring Sticky Groups
Sticky Table
To keep track of sticky connections, the ACE appliance uses a sticky table. Table entries include the
following items:
• Sticky groups
• Sticky methods
• Sticky connections
• Real servers
The sticky table can hold a maximum of four million entries (four million simultaneous users). When
the table reaches the maximum number of entries, additional sticky connections cause the table to wrap
and the first users become unstuck from their respective servers.
The ACE appliance uses a configurable timeout mechanism to age out sticky table entries. When an
entry times out, it becomes eligible for reuse. High connection rates may cause the premature aging out
of sticky entries. In this case, the ACE appliance reuses the entries that are closest to expiration first.
Sticky entries can be either dynamic (generated by the ACE appliance on-the-fly) or static
(user-configured). When you create a static sticky entry, the ACE appliance places the entry in the sticky
table immediately. Static entries remain in the sticky database until you remove them from the
configuration. You can create a maximum of 4096 static sticky entries in each context.
If the ACE appliance takes a real server out of service for whatever reason (probe failure, no inservice
command, or ARP timeout), the ACE appliance removes from the database any sticky entries that are
related to that server.
Related Topics
• Configuring Sticky Groups, page 7-11
• Sticky Types, page 7-2
• Sticky Table, page 7-11
Configuring Sticky Groups
Stickiness (or session persistence) is a feature that allows the same client to maintain multiple
simultaneous or subsequent TCP connections with the same real server for the duration of a session. A
session, as used here, is defined as a series of transactions between a client and a server over some finite
period of time (from several minutes to several hours). This feature is particularly useful for e-commerce
applications where a client needs to maintain multiple TCP connections with the same server while
shopping online, especially while building a shopping cart and during the checkout process.
E-commerce applications are not the only types of applications that require stickiness. Any Web
application that maintains client information may require stickiness, such as banking applications or
online trading. Other uses include FTP and HTTP file transfers.
The ACE appliance uses the concept of sticky groups to configure stickiness. A sticky group allows you
to specify sticky attributes. After you configure a sticky group and its attributes, you associate the sticky
group with a Layer 7 policy-map action in a Layer 7 SLB policy map.