During DNS validation, ACM searches for a CNAME in a publicly hosted zone. When it doesn't find one, it times out after 72 hours with a status of Validation timed out. You cannot use it to host DNS records for private domains, including resources in an Amazon VPC private hosted zone, untrusted domains in your private PKI, and self-signed certificates.
検証に失敗して72時間でタイムアウトする。
