ADN reliability and availability techniques Application delivery network

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1 adn reliability , availability techniques

1.1 advanced health checking
1.2 load balancing algorithms
1.3 fault tolerance

1.3.1 network based failover
1.3.2 serial based failover







adn reliability , availability techniques
advanced health checking

advanced health checking ability of adn determine not state of server on application hosted, status of application delivering. advanced health checking techniques allow adc intelligently determine whether or not content being returned server correct , should delivered client.


this feature enables other reliability features in adn, such resending request different server if content returned original server found erroneous.


load balancing algorithms

the load balancing algorithms found in today s adn far more advanced simplistic round-robin , least connections algorithms used in 1990s. these algorithms loosely based on operating systems scheduling algorithms, have since evolved factor in conditions peculiar networking , application environments. more accurate describe today s load balancing algorithms application routing algorithms, adn employ application awareness determine whether application available respond request. includes ability of adn determine not whether application available, whether or not application can respond request within specified parameters, referred service level agreement.


typical industry standard load balancing algorithms available today include:



round robin
least connections
fastest response time
weighted round robin
weighted least connections
custom values assigned individual servers in pool based on snmp or other communication mechanism

fault tolerance

the adn provides fault tolerance @ server level, within pools or farms. accomplished designating specific servers backup activated automatically adn in event primary server(s) in pool fail.


the adn ensures application availability , reliability through ability seamlessly failover secondary device in event of hardware or software failure. ensures traffic continues flow in event of failure in 1 device, thereby providing fault tolerance applications. fault tolerance implemented in adns through either network or serial based connection.


network based failover

the virtual ip address (vip) shared between 2 devices. heartbeat daemon on secondary device verifies primary device active. in event heartbeat lost, secondary device assumes shared vip , begins servicing requests. process not immediate, , though adn replicate sessions primary secondary, there no way guarantee sessions initiated during time takes secondary assume vip , begin managing traffic maintained.


serial based failover

in serial connection based failover configuration 2 adn devices communicate via standard rs232 connection instead of network, , sharing of session information , status exchanged on connection. failover instantaneous, though suffers same constraints regarding sessions initiated while primary device failing network based failover.








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