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Roy_Jee
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Jul 21, 2023

Session/Connection Management during a Failover event in a HA Peer

Hi,

Can any one explain during a failover event when secondary unit takes lead as primary how it handles sessions and on going connections,is there any stateful awareness managed at any layer as switchover is a matter of few seconds as i ahve aobservered  even connection/session mirroring is not enabled . or sessions replicated to HA peer too ?

  • This is a good question.  It all really depends on the application. 

    By default we do not mirror any connection information.  In short, afte a failover, the standby device (now active) just starts ARPing for the destination IP and it will process connection accordingly.

    Most modern web application, just open a new connection to the new active device and continue as needed.  So that may be why your seeing everything work pretty well during a failover.  

    As for timing, this depends on the failure.  If it's a user induced failover, it should be pretty seamless, possibly a second or two pause.  But if this is more of a network failure and the devices don't have a direct failover link, it could take up to 90 seconds.  Most of the time it's about 10-30 seconds.

3 Replies

  • This is a good question.  It all really depends on the application. 

    By default we do not mirror any connection information.  In short, afte a failover, the standby device (now active) just starts ARPing for the destination IP and it will process connection accordingly.

    Most modern web application, just open a new connection to the new active device and continue as needed.  So that may be why your seeing everything work pretty well during a failover.  

    As for timing, this depends on the failure.  If it's a user induced failover, it should be pretty seamless, possibly a second or two pause.  But if this is more of a network failure and the devices don't have a direct failover link, it could take up to 90 seconds.  Most of the time it's about 10-30 seconds.

    • Roy_Jee's avatar
      Roy_Jee
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      THanks for replying . But my query is about default behaviour of F5 HA as if we havent enable mirroring at any level .How much time secondary unit takes to recover failover/will secondary unit be aware of the ongoing sessions ?