Creating a new subnet group for AWS Aurora instances

I recently tried to create an AWS Aurora instance and kept getting this error message:

You cannot specify more than 3 availability zones (Service: AmazonRDS; Status Code: 400; Error Code: InvalidParameterValue; Request ID: f3947ecb-f1a2-11e6-85a4-75809343dd58)

It was hard for me to find the solution, so I'm hoping this post will help whoever runs into the same issue.

The cause of the issue is if you are using a region that has more than 3 AZs (us-east-1 has five AZs as of this post). The default subgroup automatically selects "All Available AZs" but Aurora does not support more than three. So the fix is to create a new subnet group with 3 AZs.

To create a new subnet group:

  1. Go to the RDS service page
  2. Click "Subnet Groups" on the left panel
  3. Create DB Subnet Group
  4. In the create dialog, specify name, description, and VPC
  5. In the availability zone section, make sure to only add 3 or less availability zones.

Now when you go back to the Aurora creation wizard, select your new subnet group from the dropdown.