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Benoit_C_'s avatar
Benoit_C_
Oct 06, 2015

HTTP monitor receive string : how to not take the '200 OK' into account

Hello, I have to monitor a page which give in its body 'OK' if server is OK and KO if the server is down. As a 'receive string', I use 'OK'. The problem is that 'OK' is already present in the 'HT...
application delivery
availability
BIG-IP
design
LTM
microsoft
monitor
Benoit_C_'s avatar
Benoit_C_
Oct 06, 2015

Hi Brad,

 

thanks for the answer.

 

Yes that's what I put in place: KO as a receive string.

 

But I think i'm confused because of this SOL: https://support.f5.com/kb/en-us/solutions/public/12000/800/sol12818.html (the table with results of matching)

 

Because then I could end in a situation where both 'receive string' and 'receive disable string' will match: OK because of the 'HTTP/1.1 200 OK' KO because of the body of the page

 

I'll continue to dig this and take dumps. But so far I observe a lot of flaps on servers for which I apply this monitor, and am wondering if it could be related to the strings I trying to match.

 

(For info I more or less follow the best practice 'Timeout = 3x Interval + 1')

 

Br,

 

Ben

 

  • Brad_Parker's avatar
    Brad_Parker
    Icon for Cirrus rankCirrus
    Oct 06, 2015
    You may want to think about changing your monitor to look for something other than OK if you want it to be marked down even if a 200 is being sent.
  • Benoit_C_'s avatar
    Benoit_C_
    Oct 07, 2015
    Hi Brad, yep that's what I proposed as an alternative: - give me smtg else than a OK, for example 'Valid' But devs are not willing to change this before a next release, so I'm looking at how to make it work. I'm not sure on how F5 behaves when 'reading' the HTTP response: - will LTM stop to parse it after finding the 1st occurence of an OK/KO ? (then I'm a bit stuck) - Or will it go through the entire page, count the numbers of OK or KO and take its decision ? (then it will find the KO which will 'super seed' the OK seen in the HTTP 200, and it is acceptable. Even if the matching OK won't be in the body) thanks!
  • Valentine_96813's avatar
    Valentine_96813
    Icon for Nimbostratus rankNimbostratus
    Apr 22, 2016
    Health monitors are first exact match. If there are more than one, it takes the first. I have seen issues with monitors because of this. Also, keep in mind that health monitors don't look at the entire page. https://support.f5.com/kb/en-us/solutions/public/3000/400/sol3451.html