F5 - Journeys BIG-IP LTM Migration - GTM considerations

Posting here in the technical forum for Franky-frank-reg7 

Hello all,

I'm working on migrating configurations off a pair of BIG-IP 5050 appliances to new R2800's devices. The 5050's are running code version 15.1.5 and the rseries 15.1.8, they're configured for LTM functions only, we have a separate pair of VE appliances handling BIG-DNS (GTM) functions.  I've configured new managment IP's on the new rseries appliances, installed Journeys on a VM, and created UCS config backups of the existing 5050 appliances.

My company prefers we do a per app migration due to the nature of the potential large outage associated with migrating a whole device-group (data center) in one maintenance window.

My next steps are to prepare the tenant on the rseries appliances - which as I understand means we need to configuring VLANs, trunks and interfaces on rseries appliances, deploy the tenant image and install the master key on the new tenant, prior to importing UCS files. I'm working on these steps now. 

For the migration, I was planning to import the UCS file with the interfaces on the core shutdown on the new rseries appliances, and disable all virtual servers after the UCS file is imported, configure new self IP's and enable groups of virtual servers individually in separate maintenance windows. In the Journeys documentation, there's either a full migration or application migration, I know the above is kind of hybrid approach but can someone comment on this and provide guidance?

Also, can someone explain whats required for the new appliances to connect to the GTM's? I know we'll have to create new self IP's and an iquery session with the GTM appliances. There are some basics I can use a refesher on as it relates to the GTMs. If some can describe what's required for the GTM's to support the migration along with supporting configuration examples that would be very helpful.

Lastly, as I understand it when UCS file is loaded into Journeys and deployed to new platform its translated to AS3? Does this mean we can no longer manage the virtual servers that way we did before via the GUI? I guess the questions is, if I were to choose the old approach of migrating between platforms by exporting CLI configurations and importing them to the rseries with TMSH is this supported and is there anything we need to be aware before attempting?