What is the purpose of version dates in AWS policy documents

John Skiles Skinner

10/20/23, 3:24 AM

AWS policies contain a date version. What is its purpose? In this example a bucket policy and a user policy both contain "Version": "2012-10-17" in the JSON. I don't see the purpose of the date explained in the docs.

I want to add statements from this AWS documentation show with the date 2012-10-17 to an s3 bucket policy that has existing statements with a different version date, 2008-10-17. Is this a problem? Which date should I retain?

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Tim P

10/20/23, 6:39 PM

This might help - https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_elements_version.html

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Tim

10/20/23, 7:43 PM

I'm going to copy and paste from the page Tim P linked to, so the question can be marked answered.

Short answer: it's so the policy format / language can change over time, still letting old templates work while new templates can have different format / features.

The Version policy element specifies the language syntax rules that are to be used to process a policy. To use all of the available policy features, include the following Version element outside the Statement element in all of your policies.

IAM supports the following Version element values:

2012-10-17. This is the current version of the policy language, and you should always include a Version element and set it to 2012-10-17. Otherwise, you cannot use features such as policy variables that were introduced with this version.
2008-10-17. This was an earlier version of the policy language. You might see this version on older existing policies. Do not use this version for any new policies or when you update any existing policies. Newer features, such as policy variables, will not work with your policy. For example, variables such as ${aws:username} aren't recognized as variables and are instead treated as literal strings in the policy.

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John Skiles Skinner

10/20/23, 10:41 PM

Thanks, Tims! Do we know if they're backward-compatible? Can I switch out `2008` on my existing policy for `2012` without breaking it?

Tim

10/21/23, 12:19 AM

Try it and see :)

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