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haoest_162921's avatar
haoest_162921
Icon for Nimbostratus rankNimbostratus
Jul 05, 2014

Cache or other request interception?

Hello,

 

In our production environment, we are running into some weird problems. I am not network admin, and I don't even know which model of F5 balancer we are using. But let me explain the trouble anyways. Maybe it's some obvious miss-configuration that you gentlemen have ran into.

 

We have a web form that let's the user enter some information, and submit to send back to server for processing. Sometimes, the submit never gets through the LB. Although Firebug indicates a HTTP 200 code for the POST request, in reality it never reaches IIS, and so the data was never processed. I observe that whenever this happens, the Date line in response header would contain a timestamp that is 6 minutes in the future. From what I hear, we have 2 F5 load balancers, one of which is a backup (redundancy?), that distribute traffic to 3 front-end web servers running IIS.

 

I know that persistence is turned on for at least 10 minutes. Does the LB's clock have anything to do with this behavior? Or is it some other configuration such as cache (cache should never intercept POST requests, but who knows)?

 

1 Reply

  • Kevin_Stewart's avatar
    Kevin_Stewart
    Icon for Employee rankEmployee
    Jul 05, 2014

    A few things to check:

     

    1. Are the dates/times the same on all of the IIS servers? If you're having a persistence issue, you could be load balancing to another box intermittently.

       

    2. What persistence mechanism are you using? You said something about 10 minutes, so assuming source address maybe? Since this is an HTTP-based application, consider using the built-in cookie persistence. It has no timeout value, uses less resources, and can be more reliable in most cases.

       

    3. Do you have any iRules applied to the virtual server? Is there a caching profile? If yes to either, are there any unusual configurations? A caching mechanism should indeed not affect a post, but stranger things have happened.