Wrong subnet configuration

[GandalfGrey]

hi guys

i was trying to move from single ipv4 stack to a dual stack. i've changed the default subnet to custom and enabled the ipv6, but i did a mistake, i've enabled it as internal IP. I wanted an external ip address....

now, the configuration can't be set anymore, the only solution seems to destroy the subnet and creating a new one from scratch (maybe using the same previous subnet ip allocation). But there is an issue: i have a lot of instances running on top of these IP. I can shutdown them allowing the change to the subnet , but how can I ensure that after the power on, instances, will get the same previous IPs ?

reconfiguring all operating system to use a new ip address is not a solution ,we have TONS of software relaying on this. 

[VannGuce]

For this concern, you can reserve a static external or internal IP address, depending on what IP address you want to reserve. Once an IP address (external or internal) is set to static, the IP address will never change even if the VM instance is reset or turned off.

Use this link[1][2] for more detailed information. Use also the same link as a guidance on how to reserve internal or external IP addresses.

[1]https://cloud.google.com/compute/docs/ip-addresses/reserve-static-internal-ip-address
[2]https://cloud.google.com/compute/docs/ip-addresses/reserve-static-external-ip-address

[GandalfGrey]

I can't delete the subnet as long the reserved IP is still reserved. I have to free it.