[hnov]

You pretty much have to take the same approach as you would outside of terraform: create the new thing (launch configuration, standalone instance) and attach it to the ELB before spinning down the old one. Terraform does have some rudimentary aid to that end in the form of the create_before_destroy[0] flag, though it doesn't work out with uniquely named things.

[0] https://www.terraform.io/docs/configuration/resources.html#c...