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Asked: 2024-09-25T21:32:51+05:30 In:

How can I configure an AWS S3 bucket policy using Terraform to restrict access so that only a specific user is allowed while all other users are denied?

I’m diving into configuring AWS S3 bucket policies with Terraform and I’m hitting a bit of a wall. I need to set up a bucket where only a specific user should have full access while everyone else gets denied. I know there are ways to do this, but I’m not exactly sure how to write the policy correctly in Terraform.

Here’s what I’ve got in mind: I have a user in AWS IAM, let’s say their username is `specific-user`. I want to make sure that this user can perform actions like `s3:PutObject`, `s3:GetObject`, and all those good stuff on a specific bucket, let’s call it `my-secure-bucket`. However, I want to ensure that any other users or even anonymous access get completely denied when they try to access anything in that bucket.

From what I understand, I should write a JSON policy that states that only this `specific-user` can access the bucket, but I’m not entirely sure how to implement that properly in Terraform. Should I start by defining the bucket resource first and then adding the policy? Or can I directly attach the policy to the bucket? Also, what’s the best way to structure the Terraform code to ensure that the bucket and its policy are clear and maintainable?

I’ve seen a few examples online, but they usually allow more than one user or seem overly complicated for what I need. I just want this one user to have control and have peace of mind knowing that no one else, including users from other accounts, could touch the data in that bucket.

If anyone has experience with this, could you share a simple yet effective example of what the Terraform configuration would look like? I’d really appreciate any tips or insights on how to handle this situation. Thanks!

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    2 Answers


    1. AWS S3 Bucket Policy with Terraform for a Specific User

      If you want to create an S3 bucket where only one specific user has full access while denying access to everyone else, you can do it easily using Terraform! Here’s a simple example to get you started:

      
resource "aws_s3_bucket" "my_secure_bucket" {
  bucket = "my-secure-bucket"
  acl    = "private"
}

resource "aws_s3_bucket_policy" "bucket_policy" {
  bucket = aws_s3_bucket.my_secure_bucket.id
  policy = <

      Here's a quick breakdown of what's happening:

      • We create an S3 bucket called my-secure-bucket and set its ACL to private.
      • Next, we define a bucket policy that allows specific-user to perform any action (thanks to s3:*) on the bucket.
      • Then we add a Deny statement which ensures everyone else gets denied access to the bucket, even anonymous users!

      Make sure to replace ACCOUNT_ID with your actual AWS account ID. When you run this Terraform code, it should give the desired effect of restricting access to just specific-user.

      This configuration is pretty straightforward, and you can modify it further if you need specific actions later on. Just keep your IAM policies and bucket policies separate for better clarity and maintenance!




    2. AWS S3 Bucket Policy Configuration with Terraform

      To configure your AWS S3 bucket policy using Terraform ensuring that only a specific user has access, you will first define the S3 bucket resource and then create an S3 bucket policy. In the bucket resource, you can specify the required bucket name, and then for the policy, you’ll define a JSON policy that allows only the specified user’s ARN to perform actions like `s3:GetObject` and `s3:PutObject`. Below is a simplified example of the Terraform configuration:

              
resource "aws_s3_bucket" "my_secure_bucket" {
  bucket = "my-secure-bucket"
}

resource "aws_s3_bucket_policy" "my_secure_bucket_policy" {
  bucket = aws_s3_bucket.my_secure_bucket.id
  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Effect = "Allow"
        Principal = {
          AWS = "arn:aws:iam::YOUR_ACCOUNT_ID:user/specific-user"
        }
        Action = [
          "s3:GetObject",
          "s3:PutObject"
        ]
        Resource = "${aws_s3_bucket.my_secure_bucket.arn}/*"
      },
      {
        Effect = "Deny"
        Principal = "*"
        Action = "*"
        Resource = "${aws_s3_bucket.my_secure_bucket.arn}/*"
      }
    ]
  })
}

      This configuration ensures that only `specific-user` has full access to the S3 bucket, while all other requests are denied. The second statement explicitly denies access to any other principal for any action. Ensure to replace `YOUR_ACCOUNT_ID` with your actual AWS Account ID. By structuring your code this way, you maintain clarity and can easily modify the policy later if needed. Use the `jsonencode` function to ensure your policy is properly formatted as JSON.


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