Cirrostratus
MVPSteveD1979 First I will be changing domain.com to example.com. I'm not understanding why the client would be entering application.something.gtm.example.com in the first place. Typically the way DNS is configured is you would have the following.
*** DNS at auth NS for example.com ***
application.something.datacenter.example.com 300 IN CNAME application.something.gtm.example.com
*** DNS on GTM for gtm record ***
application.something.gtm.example.com 300 IN A 1.1.1.1
application.something.gtm.example.com 300 IN A 1.1.1.2
Then the client would connect to either IP depending on what the GTM responded with while still maintaining the FQDN application.something.datacenter.example.com. Typically you wouldn't want to narrow down the FQDNs to be a specific datacenter name because that allows people to aquire more information about your infrastructure than they should.
CirrostratusRight that's how everything else we have is setup. For this situation though right now they're just using LTMs in separate datacenters. There is an A record that points to a VIP in the datacenter that is active and for a disaster recovery situation DNS would be changed to point the record to the VIP in the other datacenter. The DNS records are wildcarded *.datacenter.domain.com to 1.1.1.1 and that resolved to a VIP with the openshift routers as the pool members. Based on the application.something part of the URL Openshift knows where to route the traffic.
For this they want the developers to have a singular URL for their apps that wouldn't have to be changed in a true disaster or just a disaster recovery exercise so that would be their application.gtm.domain.com. There would be a separate WIP for each. So in a disaster situation we would just disable the pool member on the GTM for the datacenter that they weren't running out of.
The openshift configuration needs to have a route configured to know which application is being called. Right now thats the application.something.datacenter.domain.com and those engineers don't want to have to add another route (the gtm.domain.com) for each application. This is all internal traffic not exposed to the internet.
It isn't going to be a hot/hot scenerio but we wanted the developers to have one URL, traffic to know which datacenter based on the pool member enabled on the wide IP but then when it gets to the VIP on the LTM change the URL ending so that openshift still see the route and knows where to send the traffic.
When we do disaster recovery exercises not all of the applications do it at the same time so we need to be able to send some traffic to one datacenter or the other.
MVPSteveD1979 The following is what you should have for each application.
*** DNS Auth for example.com ***
application.example.com
*** DNS on GTM ***
application.gtm.example.com
Having the above configuration for each application will provide you the flexibility of being able to failover each application without much complexity on the GTM side of things. I believe it is possible to create a data-group with every application and a value of 0 or 1 and then configure an iRule to reference the data-group to check each application and it's value and failover based on that but that adds unneaded complexity to the GTM configuration.
CirrostratusThat's how we have every other application configured that have their own dedicated static VIPs on the LTMs. For this since there are so many applications hitting the same VIP and not all can be moved I thought it would be easier if i could just redirect part of the URL. I'm not sure how to do that with the datagroups but are you saying redirecting part of a URL isn't possible? I tried a policy and several irules to look for contains and replace in the URL but it wasn't working.
MVPSteveD1979 The issue here is that you have 2 different pieces handling two different parts of your request.
1. The GTM will resolve all DNS requests it is sent.
2. After you have DNS resolve you then have your request directly to the destination IP that the GTM pointed you to for lets say application1.example.com. This part of the request is not something the GTM would see because it is an application request and not a DNS request. The GTM doesn't change the original FQDN that you are attempting to resolve a destination for.