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f5starter_17204's avatar
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Nov 05, 2011

Unique FQDNs for each server port when using GTM?

When reading SOL9619: Overview of the BIG-IP GTM configuration files in the F5 Knowledgebase . I have noticed that the Pool and Server definitions have port number assigned to the pool member and virtual server respectively. Is the port number necessary in both definition?



We are using GTM to perform global site load balancing across multiple datacenters to LTMs at each data center. Each LTM is responsible for load balancing requests for multiple applications across 2 servers. Each application is listening on different port.




At a high level, this is how I see the GTM/LTM works:


1) GTM has a WideIP that maps to a pool of virtual servers (the LTMs)


2) Eash new request will have its domain name resolved, by the GTM, to an ARecord of the selected LTM


3) the LTM will in turn selects an application server(final destination) registered in its pool


4) the consumer will communicate with the application server directly for subsequent requests until the DNS TTL expires.






if I have multiple application services hosted on a single server, each listening on different port. This server is replicated across all my data centers for high availability. to access each applicaition, using F5 GTM/LTM




a) is it mandatory to define multiple FQDNs, GTM and LTM pools for the solution to work?




for example to reach each app I would use




b) or I can define 1 FQDN that maps to 1 GTM pool --> N LTM pools --> a selected server in a data center




For example to reach the same app I would use




The above (b) is what we are doing today with just the LTMs.




There are obviously gaps in my understanding of how GTM and LTM work but I hope you can understand my question and able to provide some comments on the 2 approaches.






1 Reply

  • The challenge here is how GTM should tell whether an application is available. Using your example, if you have pool1 which contains servers listening on port 2001 and pool 2 which contains servers listening on port 2002; what happens if pool 1's service goes down? Should GTM quit handing out "" even though pool2 is still up?