Adding a dynamic generic host to GTM

Question

I am attempting to load balance GTM traffic to some servers that dynamically update their IP addresses. Is there a way I can configure the GTM to update the IP address of these servers when I associate them with a WIP?

iaine · Answer

Hi
I don't think you can do this in GTM as you can in LTM with ephemeral nodes.&nbsp; A couple of altenate methods spring to mind...&nbsp;
Firstly you could do something with an iRule to intercept the DNS request as it goes to the listener, do a DNS lookup and then respond to the request based on this logic.&nbsp; This would look something like
when DNS_REQUEST {

if {[DNS::question type] eq "A"}{
        if {[DNS::question name] eq "www.test.local"}{
            set result [RESOLVER::name_lookup "/Common/dns2" www.f5.com a]
            set answer [DNSMSG::section $result answer]
            set first_rr [lindex $answer 1]
            set rdata [DNSMSG::record $first_rr rdata]
        # Generate an answer
        DNS::answer insert "[DNS::question name]. 111 [DNS::question class] [DNS::question type] $rdata"

# Stop further processing of the query after this iRule and send the answer to the client
        DNS::return
        }
    }
}
Or you could create some third party script to do a comparison between the DNS resolution or the server and the GTM Virtual Server address and then, if there are different, you can make some&nbsp; calls to update the GTM VS and Pool config.&nbsp; Below is a bash shell that I've cobbled together that shows the idea - this is very basic with no error handling so would need polishing.&nbsp; But you could use something like this either on the BIGIP and use tmsh calls or externally and make API calls - if the script ran to an acceptable schedule then GTM should be able to keep up with 3rd party DNS changes.
#!/bin/bash

#Setup some variables
#GTM Server Object Name
gtm_srv=My_Laptop
#GTM Server-Virtual Server
gtm_vs=my_server
#DNS Name to lookup
dns=(www.f5.co.uk)

#DNS lookup
dns_rec=$( dig +short $dns | grep -E '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}')
#GTM Virtual Server 
gtm_rec=$( tmsh list gtm server $gtm_srv virtual-servers { $gtm_vs { destination }} | grep -E '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | sed 's/destination//g' | cut -f1 -d":" | sed 's/^ *//g')

echo $dns_rec
echo $gtm_rec
#See if the values are different
if [ "$dns_rec" == "$gtm_rec" ]; then
    echo "DNS and GTM are equal, no change"
else
tmsh modify gtm server $gtm_srv virtual-servers delete { $gtm_vs }
tmsh modify gtm server $gtm_srv virtual-servers add { $gtm_vs { destination $dns_rec:80}}
tmsh modify gtm pool a hello members add { $gtm_srv:$gtm_vs }
    echo "GTM updated to reflect DNS change"
fi

&nbsp;

Forum Discussion

Adding a dynamic generic host to GTM

Recent Discussions

Installing a PKCS 12 File onto an F5 Device

Irule to allow specific IPs

Uploading SKCS 12 File to F5 Device

F5 not Identifying Parameter in Text/Plain Upload

Migration from physical Hardware to R series

Related Content

JA4 Part 2: Detecting and Mitigating Based on Dynamic JA4 Reputation

SSL Orchestrator Advanced Use Cases: Detecting Generative AI

Secure, Deliver and Optimize Your Modern Generative AI Apps with F5

Generate API SDK for F5 Distributed Cloud

Configure Generic Webhook Alert Receiver using F5 Distributed Cloud Platform