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About Fail-safe Mode In an HA configuration.


suzuki kensuke

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In an HA configuration, should we set the this mode on each node?

 

https://docs.citrix.com/en-us/netscaler/12/system/high-availability-introduction/configuring-fail-safe-high-availability.html

 

< CASE 1 >

Node A (Primary) Health State : NOT_UP(failed last)

Node B (Secondary) Health State : NOT_UP (failed first)

Default HA Behavior : A (Secondary), B (Secondary)

Fail-Safe Enabled HA Behavior : A (Primary), B (Secondary)

Description : If both nodes fail, one after the other, the node that was the last primary remains primary.

 

< CASE 2 >

Node A (Primary) Health State : NOT_UP (failed first)

Node B (Secondary) Health State : NOT_UP(failed last)

Default HA Behavior : A (Secondary), B (Secondary)

Fail-Safe Enabled HA Behavior : A(Secondary), B(Primary)

Description : If both nodes fail, one after the other, the node that was the last primary remains primary.

 

About CASE 1, we guess that we should enable Fail-safe Mode on Node A. 

About CASE 2, we guess that we should enable Fail-safe Mode on Node B.

 

That is we should set the this mode on each node, right?

Please could you let me know whether our understanding is correct or not? 

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You can set failsafe mode on 1 node or both; both is generally preferred. 

 

All failsafe mode does is in the few scenarios that results in two secondaries it forces a system to remain primary. It will still only force a good primary to take over.  So normal operations, same behavior as ha without failsafe mode. If a primary becomes unhealthy while staysecondary/disabled set on the current secondary node; failsafe can't override and will force unhealth primary to retain role and do what it can. The minute a the secondary can be promoted as a healthy alternative once staysecondary/disabled are removed it will.

 

If failsafe is set and everyone fails at one time, the one that was up longest/last retains the role until a healthier adc is available.  If you set it on only one node and that node is offline; then the remaining node might not be in a "failsafe" mode condition if something else were to happen.  

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