Move / Change VLAN HA pair

[#1]

Hello, 

We have two HA member in our prod environment

First HA : DNS services

Second HA : DHCP services and Grid Master
We are going to move these machines into a new vlan. Is it possible to do this operation without risk ?
During the vlan transfer, the two machines will not be able to communicate together for VRRP. I will probably have two active machines, is there any way to avoid the risk?

Kind regards, 

[#2]

First of all, I would not do this change in the middle of a production time. You would need to do the change over during a planned outage time.  There is really not enough information here to give you a definitive answer, but I will try.  Have you planned your VLAN change such that it uses the same IP subnet as before?  I would shut down one of the HA pairs before moving.  Your users will have spotty DNS services during the outage.  I would then move the shutdowned appliance first from the old VLAN to the new VLAN  and then move the appliance that is up to the new VLAN.  At this point, test the responsiveness of the VRRP address (ie can you ping the DNS address?).  If that works, then turn on the other appliance.

Hope this helps.