Folder-Level Access to S3 with AWS AIM

Program-GroupI recently had a need to grant users access toS3 but to limit access to specific folders within an S3 bucket.  While this requirement is not supported out-of-the-box, as with a traditional filesystem, you can set up IAM policies to achieve the same effect.

Background: The background for my folder-level access requirement is that we are building a system the processes data, and users should be able to write new data into S3 that the system will then process.  However, I don’t want users to access system data, and they should instead only be able to drop input data into a specific input folder.

S3 Concepts: As mentioned above, S3 is not a file system, and there are no paths, such as “/home/bob/my-file.text”.  In S3, you can create such a file but the “path” will be the file name and the slashes “/” in the file name won’t have special meaning.  Therefore, you must set up IAM policies where you define the slash “/” to be a delimiter.

s525151301783206906_p10_i1_w425S3 Buckets: You may have heard that S3 organizes data into “buckets” and you could just give different users access to different buckets.  While this is true, and easier to set up, this approach won’t scale because S3 only allows up to 100 buckets in each AWS account.

IAM Policies: In order to implement the folder-level access permissions, you will need to create policies for listing buckets, getting bucket locations, listing a specific bucket, and allowing all S3 actions in a specific folder.  With these policies you will be able to allow required Amazon S3 console permissions, allow required Amazon S3 console permissions, allow listing objects in the user’s folder, and allow all Amazon S3 actions in David’s folder.

Policy Variables: By setting up fixed IAM policies, you can get specific users set up easily.  However, if you have many users you won’t want to create the required set of policies for each user individually.  Instead you will want to use “policy variables“.  That is, instead of referring to a specific user such as “David”, you will be referring to the “username” variable: ${aws:username}.

If you have more questions about folder-level access to S3 with AWS AIM be sure to visit Jim Scharf‘s post on “Writing IAM policies: Grant access to user-specific folders in an Amazon S3 bucket“.


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