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chris_wood's avatar
chris_wood
Icon for Nimbostratus rankNimbostratus
Jun 26, 2023

Big-IP LTM - load balancing incoming request to 2 different 'paths' on Member Pool

Hi,

A strange request has come in :).  I donlt think it's possible but thought I'd reach out just encase some has an answer.

We have a VS setup that load balances to 2 different servers.

In this example we need the incoming request to load balance to a different path on each server, e.g.

incoming request > VS

VS re-writes/redirects the URL to:

Load balance to server 1 path   (https://example1/folder/folder/server1) 

Load balance to server 2 path  (https://example1/folder/folder/server2) 

Many thanks in advance!

Chris

application delivery
  • Mohamed_Ahmed_Kansoh's avatar
    Mohamed_Ahmed_Kansoh
    Icon for MVP rankMVP
    Jun 26, 2023

    Ok chris_wood , 

    This Irule Code should meet your need : 

     

    when LB_SELECTED {
if { [IP::addr [LB::server addr] equals x.x.x.x] } { 
log local0. " Server 1 selected , Change path to ( http://example/folder/folder/server1 ) "
HTTP::uri "http://[HTTP::host]/folder/folder/server1"
} elseif { [IP::addr [LB::server addr] equals x.x.x.x] } {
log local0. " Server 2 selected , Change path to ( http://example/folder/folder/server2 ) "
HTTP::uri "http://[HTTP::host]/folder/folder/server2"
}
}

#Replace "x.x.x.x" Ips by your servers/poolmembers IPs. 
#First "x.x.x.x" server1 and second "x.x.x.x" server2

     

    >> I have tested it and it works as expected , after capturing the traffic in both sides , I observerd the chaning in URI paths according to selected pool member inside the pool. 

    << Why I used this method >> ? 
    Because you need to use round Robin loadbalance technique and modify the request to servers at the same time. 

    try it and let me know. 
    Goodluck 🙂 

    • CA_Valli's avatar
      CA_Valli
      Icon for MVP rankMVP
      Jun 26, 2023

      This works, I was wondering if there was a way to make it dynamic so it was scalable ..
      I've looked into [LB::server] instruction and tested it, but it only returns server IP and pool name. 

      chris_wood if you have control on the server environment and it's possible to edit the URLs, you might want to set it up this way:
      - assign any IP address you want
      - if possible, try configuring server hostname to match the last octect ex. apache30 for IP 10.10.10.30 or apache12 for 10.10.10.12 
      - if possible, configure server URL to match the hostname, ex. /path/to/apache15 
      This way, iRule might support service scalability as server farm grows, 

       

       

      when LB_SELECTED {
  set selected [getfield [LB::server addr] "." 4]
  set server "apache$selected"
#  log local0. "server $server"
  set path "/path/to/$server" ; set host "$server.local.domain"

  HTTP::host $host 
  HTTP::path $path
}

       

       

      This will rewrite  http(s)://<virtual server url>   to    http(s)://apacheXX.local.domain/path/to/apacheXX for any given XX , without redirects (client transparent) 

    • chris_wood's avatar
      chris_wood
      Icon for Nimbostratus rankNimbostratus
      Jun 26, 2023

      Thank you! I will test this afternoon and let you know!

    • chris_wood's avatar
      chris_wood
      Icon for Nimbostratus rankNimbostratus
      Jun 27, 2023

      Hi!

      I tried your script - and looks good in the F5 logs - however the server logs aren't showing showing any connections.   

      Tried on both http/https - with the http & http-transparent profile.  I'm thinking along the lines of SSL/TLS getting in the way - might need to add 

      Removing the http profile and only using 1 server in the pool worked as expected.

      • Mohamed_Ahmed_Kansoh's avatar
        Mohamed_Ahmed_Kansoh
        Icon for MVP rankMVP
        Jun 27, 2023

        Hi chris_wood , 

        While assinging my iRule script in your virtual server, did you assign the correct pool in Virtual server resources ? 

        you sould assign a pool has 2 pool members ( and only replace first "x.x.x.x" by first pool member IP and do the same with the second pool member ip ) 

        Please Take this Packet capture to see the server and client side connections , and see the effect from F5 Bigip 

        tcpdump -nnni 0.0:nnnp -vvv -w /var/tmp/path_test.pcap host x.x.x.x

#put Client_ip address instead of "x.x.x.x"

         I will be waiting your response 

    • chris_wood's avatar
      chris_wood
      Icon for Nimbostratus rankNimbostratus
      Jun 26, 2023

      Hi Mohamed,

      Thanks for your reply.

      Basically, we want to load balance (round robin for e.g) to 2 servers in the member pool - but before passing it on to the servers, we need the Virtual Server to re-write the URL path to a different specific folder on each server:

      The reading I've done so far suggests when we use the HTTP::redirect iRule, the F5 replies directly to the client and doesn't load balance (even then sending to 2 different locations is a big ask). 

      In the mean time, we are looking into completing this task using re-directs on the individual servers, as I think that makes more sense.

  • CA_Valli's avatar
    CA_Valli
    Icon for MVP rankMVP
    Jun 26, 2023

    It's not optimal, but technically it should be possible.
    If you want to have it work dinamically, I'd suggest to configure the objects with a specific naming convention , for example referencing the path. 

    I haven't tested this code, but you could try something like this: 

    when LB_SELECTED {
  set path "/folder/folder/[LB::server name]"
}
when SERVER_CONNECTED {
  HTTP::path "$path"
}