If an instance type is specified in the install-config.yaml, the installer will try to validate its availability in the given region and that it meets the minimum requirements for OCP nodes. When that happens, the `ec2:DescribeInstanceTypes` permission is used but it's not validated by the installer as a required permissions for installs.

    4.16+

    Always by setting an instanceType in the install-config.yaml

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    If you install with an user with minimal permissions, you'll get the error:

level=error msg=failed to fetch Master Machines: failed to load asset "Install Config": failed to create install config: [controlPlane.platform.aws: Internal error: error listing instance types: fetching instance types: UnauthorizedOperation: You are not authorized to perform this operation. User: arn:aws:iam::460538899914:user/ci-op-8phprrsm-ccf9a-minimal-perm is not authorized to perform: ec2:DescribeInstanceTypes because no identity-based policy allows the ec2:DescribeInstanceTypes action
                level=error msg=	status code: 403, request id: 559344f4-0fc3-4a6c-a6ee-738d4e1c0099, compute[0].platform.aws: Internal error: error listing instance types: fetching instance types: UnauthorizedOperation: You are not authorized to perform this operation. User: arn:aws:iam::460538899914:user/ci-op-8phprrsm-ccf9a-minimal-perm is not authorized to perform: ec2:DescribeInstanceTypes because no identity-based policy allows the ec2:DescribeInstanceTypes action   
                level=error msg=	status code: 403, request id: 584cc325-9057-4c31-bb7d-2f4458336605]

    The installer fails with an explicit message saying that `ec2:DescribeInstanceTypes` is required.