Recently¹ tried to bring up a "Flexible" Postgres server (Azure's managed PG offering) on an IPv4 (four) only subnet. The request hung, for two hours, before finally failing with a generic "internal error". Retried, same result. Contact support. Flexible PG doesn't support being brought up on a vnet with IPv6, even if it is on an IPv4-only subnet, even if you have no intention of connecting to it over v6. Want that service? No IPv6 for you, I guess.
¹okay, apparently April, and even just the request to get the limitation added to their documentation of the limitations of IPv6 is still pending…
¹okay, apparently April, and even just the request to get the limitation added to their documentation of the limitations of IPv6 is still pending…