How to Set Up Amazon S3 ACL for Read-Only and Write-Once Access

How to Set Up Amazon S3 ACL for Read-Only and Write-Once Access

Amazon S3 (Simple Storage Service) is a highly scalable, durable, and secure object storage service that allows you to store and retrieve data at any time, from anywhere on the web. However, managing access to your S3 buckets can be a complex task. Today we’ll focus on how to set up Amazon S3 Access Control Lists (ACLs) for read-only and write-once access.

What Are Amazon S3 ACLs?

Access Control Lists (ACLs) in Amazon S3 are a mechanism you can use to manage access permissions to your buckets and objects. They allow you to control who can perform actions such as reading and writing data. Let’s delve into how to leverage this feature to set up read-only and write-once access.

Setting Up Read-Only Access

To allow read-only access to a bucket, you need to grant the READ permission to the user or group of users. Here’s how to do it:

1. Navigate to the Amazon S3 console.
2. Select the bucket you want to manage.
3. Go to the ‘Permissions’ tab.
4. Click ‘Access Control List’.
5. Under the ‘Access for other AWS accounts’ section, click ‘Add account’.
6. Enter the AWS account ID or the canonical user ID of the user you want to grant access to.
7. Check the ‘List objects’ box to grant read-only access.
8. Click ‘Save’.

The user now has read-only access to your bucket. They can list and read the objects but cannot write or delete them.

Setting Up Write-Once Access

Write-once access is a little more complex since Amazon S3 doesn’t directly provide a write-once permission. However, you can achieve this by combining bucket policies and AWS Lambda.

First, create a bucket policy that allows the s3:PutObject action:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {"AWS": "arn:aws:iam::ACCOUNT_ID:user/USERNAME"},
      "Action": "s3:PutObject",
      "Resource": "arn:aws:s3:::BUCKET_NAME/*"
    }
  ]
}

Next, create an AWS Lambda function that removes the s3:PutObject permission from the bucket policy after an object is uploaded. You can trigger this function using the s3:ObjectCreated:* event. Here’s an example in Python using the boto3 library:

import boto3

def lambda_handler(event, context):
    s3 = boto3.client('s3')
    bucket_name = event['Records'][0]['s3']['bucket']['name']

    s3.delete_bucket_policy(Bucket=bucket_name)

Remember to replace ACCOUNT_ID, USERNAME, and BUCKET_NAME with your details.

Conclusion

Amazon S3 provides robust mechanisms for controlling access to your data. While setting up read-only access is straightforward, write-once access requires a bit more work, involving AWS Lambda functions and bucket policies.

However, by following the steps outlined above, you can effectively manage your S3 resources and ensure your data’s security.

Remember, each organization has unique requirements, so always tailor your access controls to meet your specific needs.

Tags: Amazon S3, ACL, Access Control, Read-Only Access, Write-Once Access, AWS Lambda, Data Security, Bucket Policy

Meta Description: Learn how to set up Amazon S3 ACL for read-only and write-once access. This guide provides step-by-step instructions on managing access permissions to your Amazon S3 data.

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