Application Delivery (ADX)

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Contributor
Posts: 39
Registered: ‎05-04-2009

How long does it take to declare a server as down using L7 health checks?

How long does it take to declare a server as down using L7 health checks?

Super Contributor
Posts: 316
Registered: ‎05-01-2009

Re: How long does it take to declare a server as down using L7 health checks?

This depends on what is actually happening :-).

A ServerIron is going to declare  a real server as failed immediately in case the server is sending an incorrect  response back in reply to a layer 7 health check (incorrect means incorrect content or status code depending on the health check configuration).

There are nevertheless cases without any  response from the real server at all (NO response at layer 7). The ServerIron is trying to send health check  packets to the real servers but there is no L7 response OR the response is coming  very late (delayed). The situation is different in this case. You do have to configure  health check intervals and the amount of retries in port profiles and as well  below the configuration of healthck's and port profiles. The interval is the  time in between two health checks going to the same real server. This is as well  the timeout of a single health check try - a health check try is getting declared as failed in case  the next health check is starting. The ServerIron needs to retry the health  check as often as configured to declare a server as down based on no replies or  delayed replies. The amount of time before a real server is getting taken out of  service is therefore higher in case it is because of slow responses or no  responses at all compared to incorrect layer 7 replies.

It wait eat up "interval * (retries + 1)" to declare a server as down talking about the worst-case scenario.

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