If you specify a value for IAMCertificateId, you must also specify how you want CloudFront to serve HTTPS requests. Valid values are vip and sni-only. If you specify vip, CloudFront uses dedicated IP addresses for your content and can respond to HTTPS requests from any viewer. However, you must request permission to use this feature, and you incur additional monthly charges. If you specify sni-only, CloudFront can only respond to HTTPS requests from viewers that support Server Name Indication (SNI). All modern browsers support SNI, but some browsers still in use don't support SNI. Do not specify a value for SSLSupportMethod if you specified true for CloudFrontDefaultCertificate.