If IAMuser1 creates an s3 bucket he is the owner of the bucket. If IAMuser2 creates another IAMUser3, can he attach an identity based policy to IAMuser3 giving access to the s3 bucket created by IAMuser1?
Q: Can an IAM user give permissions to another user on a resource he does not own?
A: Yes. IAM user does not own the resource. It's the root AWS account to which the IAM user belongs own the resource.
Q: If IAMuser1 creates an S3 bucket, he is the owner of the bucket.
A: The "owner" of a bucket or an object in a bucket is not an individual IAM user, but rather the AWS account to which that user belongs.
Reference: https://acloud.guru/forums/aws-certified-solutions-architect-associate/discussion/-KPST25Z-1SVLVN7bfDW/owner-of-a-s3-bucket-file-in-s3-bucket?answer=-LEqBetBhyq9dAYn7wu9
Q: If IAMuser2 creates another IAMUser3, can he (IAMuser2) attach an identity based policy to IAMuser3 giving access to the S3 bucket created by IAMuser1?
A: It depends on what IAM permissions the IAMuser2 has. In order to give IAMuser3 access to the S3 bucket created by IAMuser1, IAMuser2 needs PutUserPolicy or AttachUserPolicy on the IAMuser3 IAM user resource.
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I have an IAM user that has full S3 access (i.e. can perform any S3 actions on any S3 resource within the AWS account). This user has created a bucket and put some files in it. The bucket has a policy which just contains an Allow rule that grants access to a different IAM user, in the same AWS account. Public access is turned off for the bucket.
Should the first user be able to access objects in this bucket? If so, is that because they created the bucket, or because they're in the account that owns the bucket? Is it possible to limit access to a bucket for users within the same AWS account?
S3 is one of the few services with resource policies, in this case they are called bucket policies.
A user in the same account has access to a (S3) resource if
nothing explicitly denies the access AND
either the bucket policy grants access OR the user / entity has a policy attached that grants access
If you wanted to restrict a bucket to a single user / entity you would
need to write a bucket policy that specifies that using a Deny statement for every user except the target one AND
either add a statement to the bucket policy or a policy attached to the user / entity granting access to the bucket.
The standard doc for understanding policy evaluation logic is this. There are other, more complicated ways to achieve your goal using e.g. permission boundaries and SCPs but they are probably overkill in your situation.
I am a AWS IAM user having "S3FullPermissions". I have created a bucket, and I want no other IAM users to access my buckets. How can I achieve it. Please help me with bucket policy..
S3 buckets and their objects are by default private. No one has access to them unless given explicit permissions to do so. So if you are the only one with S3 buckets permissions, no other IAM user will be able to access your buckets and objects.
is there a possibility for one iam user to be able to create bucket and only have full access to the bucket the user creates and NOT other buckets?
I have been reading a number of docs and watched number of videos, but I am still very confused about IAM Roles and Bucket policies. Here is what confuses me:
1) I create a bucket. At that time I can make it public or keep it private. If I make it public, then anyone, or any Application, can "see" the objects in the bucket. I think the permissions can be set to add/delete/get/list objects in the bucket. If this is the case, then why do I ever need to add any IAM Role for S3 buckets, or, add any Bucket policy (???)
2) At the time I create a bucket, can I give very specific permissions to only certain users/applications/EC2 instances etc to all or part of the bucket? e.g. App1 on EC2-X can access subfolder A in bucket B1.
3) Coming to IAM Roles, an EC2 role that gives full S3 access- what does it mean? Full access to any bucket? How can I restrict an app running on an EC2 to only certain buckets, with only certain restricted permissions (see #2) above)? Do all Apps on the EC2 have full access to all buckets? At the time of creating a bucket, can the permissions be so set that an IAM Role can be overruled?
4) Finally, what do Bucket Policies do in addition to the above IAM Roles? e.g is 'AllowS3FullAccess' a "Bucket Policy", or an "IAM Policy"? Why differentiate between types of policies- policies are just that- they define some permissions/rules on some objects/resources,as I see it.
Thanks for any clarifications.
- a newcomer to AWS
I think you are confusing permissions for resources with IAM entities.
i) There are resources (S3 bucket, EC2 instances etc.) owned by the AWS account and these resources can be accessed by IAM users, IAM roles or other AWS Services (can be from same or different account)
ii) We manage who can access and their permission level with policies
iii) Policies can be identity based (attached to IAM user/group/role) or resource based (attached to S3 bucket, SNS topic)
iv) Resource based policy will have a Principal element but the identity based policies will not have that (because the attached IAM entity is the Principal)
v) Permissions start from default deny, allow overrides the default deny and an explicit deny overrides any allow
vi) Final access will be determined by combination of all policies
To answer your questions:
1> We cannot add (or attach) an IAM role with an S3 bucket. If you want your bucket should be public (which is not recommended but need to do it till some extent if it's in use for static website), then you can keep it public
2> It is not possible while creating the bucket. You have to do it after creating the bucket via IAM and/or S3 bucket policy
3> If an IAM role has AmazonS3FullAccess, the role can (Effect:Allow) call any S3 API (s3:) for any S3 resource (Resource:) in your account (provided they don't have cross account access).
If multiple applications run on an instance with an IAM role attached and are using credentials provided by the role, their permission will be same.
4> I don't know where you got the reference AllowS3FullAccess but we cannot confirm unless we know the exact JSON. If it is attached to a bucket or has the Principal element, it is a bucket policy.
You can use IAM and Bucket policies based on your need. Usually bucket policies are used for cross account access or if you want to manage S3 permission policies in a single place.
I have four S3 buckets bucket1, bucket2, bucket3, bucket4. I would like to create a new Access/secret key that only has access to these four buckets.
How should I do this? Should I use IAM to create a new user, then login as that user, and create the S3 buckets? Would I need to create a new policy?
Create an IAM policy that only gives access to these four buckets. You do this by specifying the ARN of each bucket in the policy. Create an IAM user and assign the policy to that user. Create access keys for that user.
Here is some documentation on creating the IAM policy to grant access to specific S3 buckets.