How to Fix AWS S3 Bucket Access Denied Error

In this tutorial, you'll learn about How to Fix AWS S3 Bucket Access Denied Error. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

You try to list or access an S3 bucket and get AccessDenied — your IAM user or role lacks the required permissions.

Step-by-Step Fix

1. Check IAM user permissions

Verify the IAM user has S3 permissions:

aws iam list-attached-user-policies --user-name myuser

Expected output shows policies attached to the user:

{
    "AttachedPolicies": [
        {"PolicyName": "AmazonS3FullAccess", "PolicyArn": "arn:aws:iam::aws:policy/AmazonS3FullAccess"}
    ]
}

2. Attach S3 policy to the user

aws iam attach-user-policy --user-name myuser --policy-arn arn:aws:iam::aws:policy/AmazonS3FullAccess

3. Check bucket policy

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": "*",
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::my-bucket/*]
        }
    ]
}

Attach the policy:

aws s3api put-bucket-policy --bucket my-bucket --policy file://policy.json

4. Disable Block Public Access (if needed)

aws s3api put-public-access-block --bucket my-bucket --public-access-block-configuration BlockPublicAcls=false,IgnorePublicAcls=false,BlockPublicPolicy=false,RestrictPublicBuckets=false

5. Verify access

aws s3 ls s3://my-bucket

Expected output:

2024-01-15 10:30:00       1024 file1.txt
2024-01-15 10:31:00       2048 file2.txt

Common Mistakes

Prevention

• Use least-privilege IAM policies for S3 access.
• Enable S3 Access Logs to audit access attempts.
• Use bucket policies with conditions (source IP, VPC).
• Regularly review IAM policy attachments.

Common Mistakes with s3 bucket access

1. Using foldl instead of foldl' causing stack overflow on large lists
2. Forgetting deriving (Show, Eq) on custom data types needed for debugging
3. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable

These mistakes appear frequently in real-world AWS code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

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