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afreudenr's avatar
afreudenr
Icon for Nimbostratus rankNimbostratus
Jul 05, 2019
Solved

Pool member with sporadically listening service

We have following setup: a virtual server listening on port 80/http. Behind it is a pool member, which by default does not listen to anything. Only on manual intervention it runs acmetool (for creati...
application delivery
BIG-IP
LTM
  • Heino's avatar
    Heino
    Jul 05, 2019

    I recommend looking at how fast your monitor is configured to be (un)available. I recommend tcp_half_open (it's faster).

    A very agressive monitor could be configured:

    Interval: 1

    Up interval: Disabled (it'll be online as soon as a succesful reply is received)

    Time Until Up: 0

    Time out: (however long you want the service to be available even when there's no successful response)

    Manual resume: No

     

    Additionally; you could add an alias service port. If the pool member is 10.10.10.10:4401 but the health monitor is to check 4402, you could specifiy 4402 in your monitor.

     

    if an active pool member starts to listen on a port - how fast is F5 expected to connect to it

    However fast your monitor interval + monitor up time + pool slow ramp combination is

    Slow Ramp shouldn't prevent traffic as the intention described shouldn't generate too much of it... but you never know.

     

    Possible troubleshooting:

    Verify that you haven't configured a connection limit

     

    There's a nice little tool called tcping (for windows). In cmd/powershell try running it before starting the service. Then you can see how quickly the vIP is online.

    .\tcping.exe -t 10.10.10.10 4402

     

    The mcpd process reports in your ltm log when it sees them member back online.

Heino's avatar
Heino
Icon for Cirrus rankCirrus

I recommend looking at how fast your monitor is configured to be (un)available. I recommend tcp_half_open (it's faster).

A very agressive monitor could be configured:

Interval: 1

Up interval: Disabled (it'll be online as soon as a succesful reply is received)

Time Until Up: 0

Time out: (however long you want the service to be available even when there's no successful response)

Manual resume: No

 

Additionally; you could add an alias service port. If the pool member is 10.10.10.10:4401 but the health monitor is to check 4402, you could specifiy 4402 in your monitor.

 

if an active pool member starts to listen on a port - how fast is F5 expected to connect to it

However fast your monitor interval + monitor up time + pool slow ramp combination is

Slow Ramp shouldn't prevent traffic as the intention described shouldn't generate too much of it... but you never know.

 

Possible troubleshooting:

Verify that you haven't configured a connection limit

 

There's a nice little tool called tcping (for windows). In cmd/powershell try running it before starting the service. Then you can see how quickly the vIP is online.

.\tcping.exe -t 10.10.10.10 4402

 

The mcpd process reports in your ltm log when it sees them member back online.

afreudenr's avatar
afreudenr
Icon for Nimbostratus rankNimbostratus
Jul 05, 2019

Hi Heino - thanks a lot for the quick reply. Your tips helped me figure out what was needed to get it working. First - after using tcping - I realized that the acmetool was only listening on localhost when started (my stupid oversight). But after fixing that I still needed to play with the monitoring interval and a delay I had added as an iRule to get it working.

It works now e.g. with a 2 second tcp monitor interval and a 3 second delay in the iRule. Longer tcp intervals and shorter delays make it fail sometimes.

I'll play around a bit more with the parameters and might give the alias service port a try (which might avoid the monitor interval dependency).

It looks a lot more promising now - thanks again!