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EIT_Network's avatar
EIT_Network
Icon for Altostratus rankAltostratus
Feb 12, 2019

Health Monitor Issue

Hello Friends,

 

I am back with a new query related to F5 Health Monitor.

 

A custom Parent Monitor (http) is available (Using word available as we did'nt configure this , configured by our implementor) on F5 for one of our application pool members. SEND string is configured with some values and content and RECEIVE String is mentioned as "true".

 

Pool members are down since couple of days and during investigation while we swapping the Health Monitor from above mentioned customized monitor to "icmp". pools members and LTM VIP came UP. please help to investigate the reason for this. We are assuming this as Customized Health monitor issue OR might be problem with Pool Members end something related to their String Services. How and where to verify this.

 

Rgds

 

application delivery
LTM

13 Replies

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  • Amresh008's avatar
    Amresh008
    Icon for Nimbostratus rankNimbostratus
    Feb 12, 2019

    The SEND string that has been configured as a monitor is actually related to monitoring the services (LAYER 4) on the pool members, whereas the ping monitor checks the availability (LAYER 3 ) of the nodes forming that pool. The services may be down even if the nodes are UP. Imagine a situation in which you have built the server and assigned it an IP address which is pinging from F5 (In this case the ping monitor will show the pool to be UP). But no services or your application has been configured and hence you will not get services out of that server( the pool would be down as per the customised monitor).

     

  • Amy003_314955's avatar
    Amy003_314955
    Icon for Cirrus rankCirrus
    Feb 12, 2019

    The SEND string that has been configured as a monitor is actually related to monitoring the services (LAYER 4) on the pool members, whereas the ping monitor checks the availability (LAYER 3 ) of the nodes forming that pool. The services may be down even if the nodes are UP. Imagine a situation in which you have built the server and assigned it an IP address which is pinging from F5 (In this case the ping monitor will show the pool to be UP). But no services or your application has been configured and hence you will not get services out of that server( the pool would be down as per the customised monitor).

     

  • Amresh008's avatar
    Amresh008
    Icon for Nimbostratus rankNimbostratus
    Feb 12, 2019

    The SEND string that has been configured as a monitor is actually related to monitoring the services (LAYER 4) on the pool members, whereas the ping monitor checks the availability (LAYER 3 ) of the nodes forming that pool. The services may be down even if the nodes are UP. Imagine a situation in which you have built the server and assigned it an IP address which is pinging from F5 (In this case the ping monitor will show the pool to be UP). But no services or your application has been configured and hence you will not get services out of that server( the pool would be down as per the customised monitor).

     

  • Andy_McGrath's avatar
    Andy_McGrath
    Icon for Cumulonimbus rankCumulonimbus
    Feb 13, 2019

    Your HTTP monitor receive string is a regular expression search agains the HTTP response from the monitor request.

     

    For a very basic check set to something like ‘200 OK’ assuming that you are getting a standard OK response.

     

    The following two knowledge articles are great to help you construct a good HTTP or HTTPS monitor:

     

    K5917: Using regular expressions in a health monitor receive string

     

    K2167: Constructing HTTP requests for use with the HTTP or HTTPS application health monitor