I used eb-create
in the EB CLI to spin up a new application environment. However, when I tried to create a new database, it required me to select at least at least two availability zones from a list of four.
No matter which two I selected it would stop me with an error using the following language:
DBSubnets: Invalid option value [...] Specify the VPC ID and make sure all subnets exist.
I tried enabling the same options in the VPC configuration, but I was told this couldn't be done on an existing environment. It took me a while to find the answer, so I am posting it here.