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uni's avatar
uni
Icon for Altostratus rankAltostratus
Mar 08, 2018

Wrong monitor interval, but not failing

I was upgrading software on a box I was unfamiliar with. When rebooting, I discovered what I consider a misconfiguration in one of the monitors. I has interval 1200 and timeout 16.

The behaviour I expected here was that the monitor would take 1200 seconds to come up, then go down after 16 seconds, and stay down until the next 1200 seconds came around.

The behaviour I am seeing is it takes 1200 seconds to come up, but then stays up.

Can anyone explain this?

ltm monitor https Monitor_xxx-HTTPS {
    adaptive disabled
    cipherlist DEFAULT:+SHA:+3DES:+kEDH
    compatibility enabled
    defaults-from https
    destination *:*
    interval 1200
    ip-dscp 0
    password $M$xxxxxxxxxxxxxxxxxxxx==
    recv active
    recv-disable none
    send "GET /testpage HTTP/1.1\r\nUser-agent: F5Monitor\r\nHost: xxx.yyy.com"
    time-until-up 0
    timeout 16
    username f5monitor@yyy.com
}
application delivery
LTM
monitor interval

3 Replies

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  • JG's avatar
    JG
    Icon for Cumulonimbus rankCumulonimbus
    Mar 08, 2018

    The monitor times out after 16 seconds if unsuccessful, and will not try again until after 1200 seconds, making it, effectively, ineffective in catching a service status change soon enough.

     

    The settings should probably be returned to the default:

     

    • Interval: 5 seconds;

       

    • Timeout: 16 seconds.

       

    as it is hardly normal for the monitor to take 1200 seconds to receive a response, and the timeout value should be 3 times the interval as recommended by F5.

     

    [EDITED]

     

  • Simon_Blakely's avatar
    Simon_Blakely
    Icon for Employee rankEmployee
    Mar 09, 2018

    The monitor issues a status check every 1200 seconds. If a status check does not get an OK response within 16 seconds, it will be marked down.

     

    If the first check attempt fails to get a response before the timeout period (16 seconds), the member is marked down.

     

    The next check will be 1184 (1200-16) seconds after the pool is marked down. If the pool member responds within 16 seconds, then the member will be marked up and will stay marked up until the next check 1200 seconds later.

     

    Is that clear?