Amazon S3:

Amazon S3 buckets are a reference to a hostname within a URL.

For example, a bucket named amazon-1 translates as http://amazon-1.s3.amazonaws.com; Amazon states that this is a known limitation. 

Though buckets can be named with any alpha-numeric character, follow some simple naming rules to ensure that you can reference your bucket using the .s3.amazonaws.com convention.
Refer to the following Amazon S3 link to know more about how to create buckets and its limitations.

https://docs.aws.amazon.com/AmazonS3/latest/UG/CreatingaBucket.html

Ensure the bucket names meet following System Recovery 2013 R2 SP6 requirements:

• Bucket names can contain lowercase letters, numbers, and dash (or hyphens).
• Bucket names cannot begin or end with a hyphen (-).
• System Recovery does not support buckets names having a period (.).

 

Microsoft Azure: Ensure that the container names meet following System Recovery 16 SP2 requirements:
A container name must be a valid DNS name, conforming to the following naming rules:

• Container names must start with a letter or number, and can contain only letters, numbers, and the dash (-) character.
• Every dash (-) character must be immediately preceded and followed by a letter or number; consecutive dashes are not permitted in container names.
• All letters in a container name must be lowercase.
• Container names must be from 3 through 63 characters long.

Ensure that the blob names meet following System Recovery 16 SP2 requirements:
A blob name must conforming to the following naming rules:

• A blob name can contain any combination of characters.
• A blob name must be at least one character long and cannot be more than 1,024 characters long.
• Blob names are case-sensitive.
• Reserved URL characters must be properly escaped.
• The number of path segments comprising the blob name cannot exceed 254. A path segment is the string between consecutive delimiter characters (for example, the forward slash '/') that corresponds to the name of a virtual directory.

Note: Avoid blob names that end with a dot (.), a forward slash (/), or a sequence or combination of the two.

The Blob service is based on a flat storage scheme, not a hierarchical scheme. However, you may specify a character or string delimiter within a blob name to create a virtual hierarchy. For example, the following list shows valid and unique blob names. Notice that a string can be valid as both a blob name and as a virtual directory name in the same container:

• /a
• /a.txt
• /a/b
• /a/b.txt

You can take advantage of the delimiter character when enumerating blobs.