I am in a situation where I need to migrate a bunch of nodes to a new app without first removing them from their original app.
I was wondering what would happen if two separate apps have the same node appEUI, DevEUI, AppKey entered for an OTAA activation, does the node join with the first app it receives a Join response from?
Can’t be done with the data integrity constraints on the stack.
You just have to script it in advance so it exports, deletes & imports on each device at a time.
Or, given realistic packet loss expectations, export all, delete all & import all which will be much faster.
That is a bit tricky. The issue is that the nodes currently report to an app which is running on a private thethingsindustries stack. Since the company has gone under and there is no more support, I need to migrate the nodes to TTN V3 without having any access to current app server.
I do have local access to the devices, so I can force them to re-join at will.
On their own server or a hosted instance under TTI?
If the former I’m sure someone must be willing to shut down the server if not already done (contact the bust companies administrator/auditor) - they will want to minimise costs before creditor recovery - unless they are trying to sell as a going concern - in which case your actions might be premature! (& potentially unuthorised?!). If the latter I’m sure the TTi team wont want to keep instance up if no one paying the bills! 
- A quick note to core team to highlight? (Then you can re-instance on V3 with it taking the slack after next session initiates?)
Company =???
Update: another thought - who owns the nodes? Are they a company asset? If so even if folded you may be acting without authority - if end client owned (was company delivering a managed service?) then they could potentially act independently to action - thouh they may need to ‘determine’ any contract 1st and provide notice to the Company liquidators/administrators… IANAL!
The nodes and gateways belong to the client using them. The business model consisted of first selling the nodes and gateways and then charging a monthly fee for network usage. So the nodes and gateways have been paid by and belong to the client according to the service contract.
I suppose the last resort option is to just change the AppEUI for every node
Having now provided the not inconsequential detail that the devices are on a totally different database, go for your life.
The gateways, when migrated over to TTN, will then join up the dots
If the GW’s are also migrated to TTN V3 they will no longer feed the node data through to the private instance in any event starving the old instance of join request or data even if still live! Registering both gw’s and nodes in TTN V3 will then mean they act as one system independent of any history 
Just go for it !
Remember to re-instate any applications/integrations along with the node details and you then should be able to extract the delivered data as before…