Amazon S3 Bucket Naming Requirements
The Amazon S3 bucket that you use to store CloudTrail log files must have a name that conforms with naming requirements for non-US Standard regions. Amazon S3 defines a bucket name as a series of one or more labels, separated by periods, that adhere to the following rules:
The bucket name can be between 3 and 63 characters long, and can contain only lower-case characters, numbers, periods, and dashes.
Each label in the bucket name must start with a lowercase letter or number.
The bucket name cannot contain underscores, end with a dash, have consecutive periods, or use dashes adjacent to periods.
The bucket name cannot be formatted as an IP address (198.51.100.24).
Because S3 allows your bucket to be used as a URL that can be accessed publicly, the bucket name that you choose must be globally unique. If some other account has already created a bucket with the name that you chose, you must use another name. For more information, see Bucket Restrictions and Limitations in the Amazon Simple Storage Service Developer Guide.