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Cisco ACE: Using Backup Server Farm to Dynamically add Servers






In Cisco ACE configuration Real servers are dedicated physical servers that you typically configure in groups called server farms. Server farms are groups of networked real servers that contain the same content and that typically reside in the same physical location in a data center. Web sites often comprise groups of servers configured in a server farm. Load-balancing software distributes client requests for content or services among the real servers based on the configured policy and traffic classification, server availability and load, and other factors. If one server goes down, another server can take its place and continue to provide the same content to the clients who requested it.
This document describes steps to use to add an extra device to the server farm and in case of failure fall back to the original server farm.





The existing server farm has 3 operational servers configured and working properly. You need to add an additional device, like cache server, so that if the cache server (let's call this vc130) is up and running, it should send all traffic to this server. If the cache server is down, on not replying on port 80, it should fall back to this current scenario.



Initial Configuration


probe tcp PROBE_TCP
  port 80
  interval 5

rserver host ns123
  ip address
  conn-limit max 50000 min 40000
rserver host ns124
  ip address
  conn-limit max 50000 min 40000
rserver host ns125
  ip address
  conn-limit max 50000 min 40000

serverfarm host FARM_WEB
  predictor leastconns
  probe PROBE_TCP
  rserver ns123
  rserver ns124
  rserver ns125

parameter-map type http HTTP_PARAMETER_MAP
  set header-maxparse-length 65535
  set content-maxparse-length 65535
  length-exceed continue
  parsing non-strict

sticky http-cookie ACE-Insert web-sticky
  cookie insert browser-expire
  serverfarm FARM_WEB
  timeout 5

class-map match-all L4-WEB-IP
  2 match virtual-address [my ip] tcp eq www

policy-map type loadbalance http first-match WEB_L7_POLICY
  class class-default
    sticky-serverfarm web-sticky
    insert-http x-forward header-value "%is"

policy-map multi-match WEB-to-vIPs
  class L4-WEB-IP
    loadbalance vip inservice
    loadbalance policy WEB_L7_POLICY
    loadbalance vip icmp-reply active
    nat dynamic 1 vlan [my vlan]
    appl-parameter http advanced-options HTTP_PARAMETER_MAP





Configure a new serverfarm, add real servers etc and put that serverfarm as backup serverfarm under L7 policy map. So, for example, you have serverfarm "test" which you want as back up.

policy-map type loadbalance http first-match WEB_L7_POLICY
  class class-default
    sticky-serverfarm web-sticky backup test  ----->  This is where you will specify the backup serverfarm.
    insert-http x-forward header-value "%is"


You will have probes etc in the same way as you have for regular serverfarm. You can also use backup command under sticky group and specify the backup serverfarm there with sticky keyword. But remember if you have sticky configured for backup serverfarm, even when the primary serverfarm comes back as "operational", the connections which have sticky entry in DB for servers in backup serverfarm, will continue to be served by the backup serverfarm.

For example if your primary serverfarm is APP1-SF1 & Backup serverfarm is APP1-SF2 you need to configure the following.

sticky ip-netmask address source APP1-sticky
timeout 60
serverfarm APP1-SF1 backup App1-SF2 sticky
  --->  This will ensure that sticky is applied to backup serverfarm too



Related Information

Configuring Real Servers and Server Farms
ACE dynamic configuration

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