Re-balance requests from a single client

Hi!

 

Welcome to the world of iRules!

 

A few tips:

 

• The LB::reselect can't be used in the HTTP_REQUEST.
• Also, tables has an inbuilt expiration you can use.

/Patrik

 

Try this one:

when RULE_INIT {

    set static::lifetime 60
    set static::requestlimit 10

}

when LB_SELECTED {

    if { [HTTP::header "User-Agent"] contains "Mozilla" } {

        Add a table entry with a lifetime in seconds of the value of $lifetime.
        table add [IP::client_addr] 1 indefinite $static::lifetime

        if { [table incr [IP::client_addr]] > $static::requestlimit } {
            If the user has surpassed the request limit the pool member is reselected
            log local0. "This server was selected: [LB::server]"
            LB::reselect
            log local0. "Selected [LB::server]"
        }
    }
}

/Patrik

Hi Patrik,

 

Thanks for your reply! I'll edit the static::lifetime portion down to 2 and test this out.

 

Hi Patrik,

 

I looked over your suggestion again and I have a concern/question about using the LB_SELECTED tag. Will this rule only come into affect when a connection from the specified user-agent is initially opened?

 

Specifically, the issue we're seeing is that there is only one connection from the device, so to my thinking, the LB is only selected once, but a very large number of requests.

 

Does LB::reselect only work within LB_SELECTED, and if so, is there a similar function that would work under HTTP_REQUEST?

 

Thanks again! Jody

 

Hi Jody!

I see what you mean, and you have a point, and I did not know the answer. So I did an experiment. Set the maximum connections in firefox to 1 and then added the following rule on my VIP:

when CLIENT_ACCEPTED {
    log local0. "New connection. Client port [TCP::client_port]"
}

when LB_SELECTED {
    log local0. "LB Selected. Client port [TCP::client_port]"
}

This is the log

Mar 14 09:09:16 LB1 info tmm2[12112]: Rule /Partition/iruletest : New connection. Client port 18482
Mar 14 09:09:17 LB1 info tmm2[12112]: Rule /Partition/iruletest : LB Selected. Client port 18482
Mar 14 09:09:17 LB1 info tmm2[12112]: Rule /Partition/iruletest : LB Selected. Client port 18482

Looks like it's triggered everytime.

IF it does not work, we could try to reselect the member via the pool command in the HTTP_REQUEST event, but it will be messier. 🙂

/Patrik

Hi again!

 

Have you managed to solve your issue yet?

 

I did some further tests today for another thing and it turns out that what I saw must have been a fluke.

 

The LB_SELECTED event is only activated once (per pool selection), and this causes a problem for you since the LB::reselect command only seems to be valid in the LB_SELECTED event.

 

I have an idea for a solution using tables but I'd rather know if you've solved it before tampering with it later tonight.

 

/Patrik

 

I think I figured it out. I wrote and iRule and tried it on a virtual server having a default pool with two members. The load balancing method was predictive.

The result seems to be what you want. There was no interruptions to the requests and the server was changed as planned.

when RULE_INIT {

    set static::lifetime 60
    set static::requestlimit 5
    set static::debug 1
}
when CLIENT_ACCEPTED {
    log local0. "New connection"
}

when HTTP_REQUEST {

    if { [HTTP::header "User-Agent"] contains "Mozilla" } {
        Add a table entry with a lifetime in seconds of the value of $lifetime.
        table add [IP::client_addr] 1 indefinite $static::lifetime

        Check if the limit has been reached
        if { [table incr [IP::client_addr]] > $static::requestlimit } {
            Delete the table entry to restart the timeout
            table delete [IP::client_addr]
            if { $static::debug } { log local0. "Before select [LB::server addr]" }
            Disconnect the server session
            LB::detach
            Force a new load balancing decision based on the current load
            eval [LB::select]
            if { $static::debug } { log local0. "After select [LB::server addr]" }
        }   else {
            if { $static::debug } { log local0. "Connections still ok" }
        }
    }
}

Added some debug options for testing it, but you can remove them (and the whole CLIENT_ACCEPTED event.

To test it I wrote a powershell script that sends a request every 3 seconds and echoes the result. Since it's only using one session (can be verified by the fact that CLIENT_ACCEPTED logging only is triggered once) it could be used to simulate the calls made by your service.

Create a web client object
$wc = New-Object System.Net.WebClient 

while(0 -lt 1){
    Add headers
    $wc.Headers.Add("User-Agent", "User-Agent: Mozilla/4.0 (compatible; MSIE 7.0;)") 
    "Sending a request"
    $result = $wc.DownloadString("https://www.mysite.com") 
    Echo request result
    $result
    Wait for 3 seconds before sending the next one
    sleep 3
}

Hope it works for you!

/Patrik

do you know/can you explain why LB::reselect can't be used within HTTP_REQUEST, but LB::detach and LB::select can be?

 

For lack of a better answer, this has to do with event timing. The HTTP_REQUEST event triggers when the VIP consumes the request headers, but has not yet made a load balancing decision. You can preemptively cause a load balancing selection with LB::select (and perhaps detach that with LB::detach), but you can't reselect something that hasn't been selected yet.

 

Hi!

 

Just out of curiousity, did it work as expected?

 

/Patrik