Session Persistence Using Cookie Insert on the Cisco Application Control Engine Configuration Example
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Contents |
Goal
Configure basic load balancing with cookie insert where client traffic enters on one network and is directed to servers residing on a second network. Once the client has entered the site they will remain stuck to a given server based on a HTTP Cookie inserted by ACE.
Design
Clients will send application requests through the multilayer switch feature card (MSFC), which routes them to a virtual IP address (VIP) within the Cisco® Application Control Engine (ACE). The VIP used in this example resides in an ACE context, which is configured with a client VLAN and a server VLAN (see figure below). Client requests will arrive at the VIP, and the ACE will check the request to see if it contains a cookie. If it does, the sticky table will be checked to see which server should receive the request. If the cookie entry has expired, or if the client does not have a cookie the ACE will pick the appropriate server to receive the request based on the requested URL. When the server responds ACE will insert a cookie into the HTTP Response to so that upon future requests client persistence to the server will be maintained.
Within the Cisco ACE sticky resources are finite and are controlled via resource allocation. Before a context can apply session persistence using sticky groups, the context must first be given a sticky allocation. Once this is done, a sticky group is created to define parameters and the serverfarm where client requests will be sent. Recall, the load balancing action tells ACE how to handle traffic which has hit a VIP. Thus the sticky group on ACE is applied within the load balance policy-map. To enable server load-balancing with session persistence based on cookies ACE inserts you need to do the following:
- Allocate sticky resources to the context
- Enable ACLs to allow data traffic through the ACE device, as it is denied by default.
- Configure the IPs of the servers (define rservers)
- Group the real servers (create a serverfarm)
- Create a sticky group
- Define the virtual IP address (VIP)
- Define how traffic is to be handled as it is received (create a policy map for load balancing)
- Apply the sticky group to the load balancing policy
- Associate a VIP to a handling action (create a multimatch policy map [a service policy])
- Create client- and server-facing interfaces
- Apply the VIP and ACL permitting client connections to the interface (apply access group and service policy to interface)
 | Note: | For brevity only the bold steps are covered in this document. Please review the URL Load Balancing using Routed Mode document for more information on basic URL load balancing and the base configuration. |
To begin the configuration, allocate sticky resources to the context you will be using In this example a context “routed” has already been defined. Create a resource class, allocate the desired amount of sticky entries, and apply them to the “routed” context.
ACE-1/Admin# show run | begin routed context routed allocate-interface vlan 10 allocate-interface vlan 20 allocate-interface vlan 40 ACE-1/Admin(config)# resource-class sticky ACE-1/Admin(config-resource)# limit-resource all minimum 0.00 maximum unlimited ACE-1/Admin(config-resource)# limit-resource sticky minimum 10.00 maximum equal-to-min ACE-1/Admin(config)# context routed ACE-1/Admin(config-context)# member sticky
| Note: | At this time sticky resources are a fixed resource outside the other resources. Thus you must use maximum equal-to-min and you must define sticky resources even is all is previously used. This also applies to the Admin context. |
Once the resources have been allocated a sticky group can be defined. The Cisco ACE can be configured in various ways to apply session persistence using cookies. For this example cookie insert will be used. The cookie name ACE will insert is supplied when the sticky group is created. By default ACE inserts permanent cookies which have a timeout of 24 hours. Using the configuration below ACE will insert a cookie with the name “ACE-Insert”, it will have a timeout of 5 minutes, and use a pre-existing serverfarm named “webfarm”.
ACE-1/routed(config)# sticky http-cookie ACE-Insert web-sticky ACE-1/routed(config-sticky-cookie)# cookie insert ACE-1/routed(config-sticky-cookie)# timeout 5 ACE-1/routed(config-sticky-cookie)# serverfarm webfarm
| Note: | If session cookies (cookies that are removed when the client closes the browser) are preferred then “cookie insert browser-expire” can be configured. |
The serverfarm within the load balancing policy map must be swapped with the sticky group to apply cookie-insert sticky to new client requests. Based on this example configuration there are two possible actions for handling new client requests. Any requests for images will be sent to the “imagefarm” serverfarm, which does not require persistence. All other requests will be sent to the web servers in the “webfarm” where the clients will use session persistence.
ACE-1/routed(config)# policy-map type loadbalance http first-match slb-logic ACE-1/routed(config-pmap-lb-c)# class class-default ACE-1/routed(config-pmap-lb-c)# no serverfarm webfarm ACE-1/routed(config-pmap-lb-c)# sticky-serverfarm web-sticky
| Note: | Changing from a serverfarm to a sticky group is potentially service impacting. While current connections will be allowed to finish, new connections will not be accepted during the removal of the serverfarm and applying the sticky group to the load balance policy. |
When cookie insert is applied permanent entries are inserted into the static sticky database for each real server defined in the serverfarm. In this example there are two entries created.
ACE-1/routed(config-pmap-lb-c)# do show sticky database static sticky group : web-sticky type : HTTP-COOKIE timeout : 5 timeout-activeconns : FALSE sticky-entry rserver-instance time-to-expire flags ---------------------+----------------------+--------------+-------+ 16820511103801384579 lnx1:0 never - sticky group : web-sticky type : HTTP-COOKIE timeout : 5 timeout-activeconns : FALSE sticky-entry rserver-instance time-to-expire flags ---------------------+----------------------+--------------+-------+ 3347854103021350619 lnx2:0 never -
| Note: | The “sticky-entry” is a hash of the cookie-value set by ACE for the real server. It will not appear in a sniffer trace or on the client browser. See the comment section below for determining which server a client is associated to via the cookie value. |
When a client connects to the VIP they download index.html page from the web servers. At this point the client will get a cookie for the selected server to ensure all future requests will continue to use the same server. While there is no way to see how many clients have a cookie for a given server the common show commands will provide details on the incoming requests and responses and other data stats.
Recall, the Cisco ACE inserts a static entry for each server in a server farm in the sticky group. In this case there is only one sticky group and it uses cookie-insert and the serverfarm contains 2 real servers. Thus the output of the show stats sticky command displays 2 entries, despite the number of clients using the VIP.
ACE-1/routed# show stats sticky +------------------------------------------+ +----------- Sticky statistics ------------+ +------------------------------------------+ Total sticky entries reused : 0 prior to expiry Total active sticky entries : 2 Total active sticky conns : 0 Total static sticky entries : 2
Related show commands
This section provides information you can use to confirm your configuration is working properly.
Certain show commands are supported by the Output Interpreter Tool (registered customers only), which allows you to view an analysis of show command output.
ACE-1/routed #show sticky database static ACE-1/routed #show service-policy client-vips ACE-1/routed #show service-policy client-vips detail ACE-1/routed #show serverfarm ACE-1/routed #show rserver ACE-1/routed #show stats
Comments
The type of cookie ACE will insert depends on if cookie-insert is configured or cookie-insert browser-expire is configured. The sniffer traces below show the difference between the types of cookies ACE will insert.
ACE configured with “cookie insert”
Hypertext Transfer Protocol
HTTP/1.1 200 OK\r\n
Set-Cookie: ACE-Insert=R4052451851; path=/; expires=Thu, 16-Oct-2008
00:08:55 GMT\r\n
Date: Fri, 29 Aug 2008 19:17:35 GMT\r\n
Server: Apache/2.0.52 (Red Hat)\r\n
Accept-Ranges: bytes\r\n
Content-Length: 1112\r\n
VirtualHost: 192.168.1.12\r\n
Connection: close\r\n
Content-Type: text/html; charset=UTF-8\r\n
\r\n
ACE configured with “cookie insert browser-expire”
Hypertext Transfer Protocol
HTTP/1.1 200 OK\r\n
Set-Cookie: ACE-Insert=R4052450762; path=/\r\n
Date: Fri, 29 Aug 2008 19:31:58 GMT\r\n
Server: Apache/2.0.52 (Red Hat)\r\n
Accept-Ranges: bytes\r\n
Content-Length: 353\r\n
VirtualHost: 192.168.1.11\r\n
Connection: close\r\n
Content-Type: text/html; charset=UTF-8\r\n
\r\n
Notice the two cookie values do not appear to be related to the sticky-value in the show sticky database static output, displayed below:
sticky-entry rserver-instance time-to-expire flags
---------------------+----------------------+--------------+-------+
16820511103801384579 lnx1:0 never -
<…snip…>
3347854103021350619 lnx2:0 never -
This is because the sticky-entry is a hash of the cookie value. In order to determine the server a client is hitting one must mark the server such that it can be distinguished, possibly using a HTTP Header in the server response, or by determining the cookie value ACE uses for each server. The cookie value is a number based on the serverfarm name, rserver name, and rserver port. The following script can be used to determine the values associated with each rserver.
[root@host cookie]# ./ace-cookie-value.tcl webfarm lnx1 0
Value: R4052451851
[root@host cookie]# ./ace-cookie-value.tcl webfarm lnx2 0
Value: R4052450762
#!/usr/bin/tclsh
#######################################################################
# #
# Name: ace-cookie-value.tcl #
# #
# This script takes the serverfarm name, the real server name and the #
# port number used by ACE and returns the generated hash that will be #
# used for cookie insertion. #
# #
#######################################################################
if { $argc != 3 } {
puts "[info script] <serverfarm> <realname> <port>"
exit 0
}
set serverFarmName [lindex $argv 0]
set realServerName [lindex $argv 1]
set port [lindex $argv 2]
set hashValue 5381
set hashMultiplier 32
set cookieInsertStr "$serverFarmName:$realServerName:$port"
set len [ string length $cookieInsertStr ]
for { set ix 0 } { $ix < $len } { incr ix } {
set hashValue [expr (($hashValue * $hashMultiplier) + $hashValue) \
+ [scan [string index $cookieInsertStr $ix] %c]]
}
puts [format "Value: R%u" $hashValue]
show running-config
ACE-1/routed# show run
Generating configuration....
access-list everyone line 8 extended permit ip any any
access-list everyone line 16 extended permit icmp any any
rserver host lnx1
ip address 192.168.1.11
inservice
rserver host lnx2
ip address 192.168.1.12
inservice
rserver host lnx3
ip address 192.168.1.13
inservice
rserver host lnx4
ip address 192.168.1.14
inservice
serverfarm host imagefarm
rserver lnx3
inservice
rserver lnx4
inservice
serverfarm host webfarm
rserver lnx1
inservice
rserver lnx2
inservice
sticky http-cookie ACE-Insert web-sticky
cookie insert browser-expire
timeout 5
serverfarm webfarm
class-map type http loadbalance match-all images
2 match http url /images/.*
class-map match-all slb-vip
2 match virtual-address 172.16.1.101 any
policy-map type management first-match remote-access
class class-default
permit
policy-map type loadbalance http first-match slb
class images
serverfarm imagefarm
class class-default
sticky-serverfarm web-sticky
policy-map multi-match client-vips
class slb-vip
loadbalance vip inservice
loadbalance policy slb
interface vlan 20
description "Client Side"
ip address 172.16.1.5 255.255.255.0
access-group input everyone
service-policy input client-vips
no shutdown
interface vlan 40
description "Default gateway of real servers"
ip address 192.168.1.1 255.255.255.0
service-policy input remote-access
no shutdown
ip route 0.0.0.0 0.0.0.0 172.16.1.1
