5.2 Bucket Policies and IAM Roles

Bucket Policies:

  • Define access permissions directly on S3 buckets.
  • Manage who can access and what actions they can perform on the data within the bucket.
  • Support JSON-based policies for precise control.

S3 Bucket policy

Purpose of Bucket Policies

  • Access Control: They primarily serve to grant or deny access to the S3 buckets and objects to various users and services within or across AWS accounts.
  • Security: Enhance the security of your S3 resources by ensuring only authorized access is allowed, based on a wide range of conditions like IP addresses, HTTP referrer, etc.
  • Compliance: Help in enforcing compliance requirements by strictly controlling who can access what resources.

Features of Bucket Policies

  • JSON-Based: Bucket policies are written in JSON (JavaScript Object Notation) and specify the Permissions (actions), Resources (buckets and objects), and Principals (users, accounts, roles) involved.
  • Conditions: Policies can include conditions for when the permissions apply, such as restricting access to specific IP ranges or requiring the use of MFA (Multi-Factor Authentication) for deleting objects.

Use Cases

  1. Public Website Hosting: Granting public read access to an S3 bucket to serve static assets for a website, while keeping write access restricted to authorized users.
  2. Cross-Account Access: Allowing users or services in one AWS account to access resources in an S3 bucket owned by another account, which is useful in collaborative projects or multi-departmental organizations.
  3. Log Storage and Access: Storing access logs in S3 and using bucket policies to allow access only to specific auditing or monitoring services.
  4. Data Lake Security: Implementing fine-grained access control in a data lake architecture, ensuring that only authorized users and applications can access sensitive data stored in S3.
  5. Regulatory Compliance: Enforcing access restrictions required by regulations such as GDPR, HIPAA, etc., by controlling who can access or manipulate the data in S3.

Implementing S3 bucket policies correctly is critical for the security and compliance of applications that use AWS S3 for storage. AWS provides a policy generator tool that can help in creating these policies by specifying the desired permissions, resources, and conditions, making it easier to get started with advanced access control configurations.

To create a bucket policy in AWS S3:

Via AWS Console:

  1. Open the Amazon S3 console.
  2. Navigate to the bucket you want to create a policy for.
  3. Click on the “Permissions” tab.
  4. Under “Bucket Policy,” click “Edit” and enter your policy in JSON format.
  5. aws s3 bucket policy

Using AWS CLI:

  1. Write your bucket policy in a JSON file.
  2. Use the command:
aws s3api put-bucket-policy --bucket [BUCKET_NAME] --policy file://[POLICY_FILE.json]
--- Policy_File.Json 
  "Version": "2012-10-17",
  "Statement": [
      "Sid": "ExampleStatement",
      "Effect": "Allow",
      "Principal": "*",
      "Action": [
      "Resource": [

Objective: Creating a bucket policy is crucial for managing access to the data in your S3 bucket. It allows you to specify permissions (who can access and what actions they can perform) at the bucket level, providing a granular control over the security and accessibility of your stored data. This ensures that your S3 data is accessed only by authorized users or services according to the defined policies.

IAM Roles

IAM Roles are a fundamental component of AWS security, enabling you to securely delegate permissions and manage access to your AWS resources.

What is an IAM Role?

An IAM Role is an AWS Identity and Access Management entity that defines permissions for making AWS service requests. Unlike traditional user credentials, IAM Roles are not associated with a specific user or AWS resource. Instead, roles are assumed by AWS services, users, or resources with the appropriate permissions.

Key Benefits of IAM Roles

IAM Roles offer several key benefits for managing access to AWS resources:

1. Fine-Grained Access Control

IAM Roles allow you to grant specific permissions to trusted entities, such as AWS services, EC2 instances, or other AWS accounts, without exposing long-term credentials like access keys. This fine-grained control helps minimize the risk of unauthorized access.

2. Security Best Practices

IAM Roles align with AWS security best practices by adhering to the principle of least privilege. This means granting only the permissions necessary for a specific task, reducing the potential for security vulnerabilities.

3. Temporary Credentials

When a role is assumed, it provides temporary security credentials, including an access key, secret access key, and session token. These credentials have a limited lifespan, reducing the risk of misuse if they are compromised.

4. Seamless Integration

IAM Roles seamlessly integrate with various AWS services, making them an essential component for enabling cross-service functionality, such as granting an EC2 instance access to an S3 bucket or enabling Lambda functions to interact with other AWS resources.

Common Use Cases for IAM Roles

IAM Roles are versatile and can be used in numerous scenarios, including:

  • EC2 Instance Profiles: Granting EC2 instances permissions to access other AWS services without embedding credentials within the instances.
  • S3 IAM Roles: Granting S3 specific Bucket permissions to the Users
  • Cross-Account Access: Enabling resources in one AWS account to access resources in another AWS account securely.
  • Federated Access: Allowing users federated through identity providers (e.g., SAML or OpenID Connect) to assume roles with temporary credentials.
  • AWS Lambda: Authorizing AWS Lambda functions to interact with AWS resources on your behalf.
  • Service-to-Service Access: Allowing AWS services, like Amazon S3, to assume roles to access other resources.

Getting Started with IAM Roles

Creating and managing IAM Roles is done through the AWS Management Console, AWS CLI, or AWS SDKs. You’ll define the permissions, specify who can assume the role, and then securely grant access to trusted entities.

Ready to dive in? Explore our comprehensive documentation and tutorials to harness the power of IAM Roles in securing and managing access to your AWS resources.

Start your journey into IAM Roles today, and take control of your AWS security and access management!

Creating an IAM Role for S3 Bucket using AWS Management Console:

  1. Sign in to your AWS Management Console.
  2. Go to the IAM (Identity and Access Management) service.
  3. In the left navigation pane, select “Roles.”
  4. Click the “Create role” button.
  5. Choose the trusted entity type. Since you want to grant access to an S3 bucket, you can select “AWS service” as the trusted entity type and then choose “S3” as the use case. Click “Next: Permissions.”
  6. In the “Attach permissions policies” step, you can either attach existing policies or create a custom policy. To keep it simple, you can attach the “AmazonS3FullAccess” policy, which provides full access to S3 resources. Click “Next: Tags” if you want to add tags, or just click “Next: Review” to proceed.
  7. Provide a meaningful name for the role, e.g., “S3BucketAccessRole,” and optionally add a description. Click “Create role.”
  8. The IAM role for S3 bucket access is now created. You’ll see a confirmation screen. You can now use this role to grant access to your S3 bucket.

Creating an IAM Role for S3 Bucket using AWS CLI:

Below are the steps to create an IAM role for an S3 bucket using the AWS CLI. Make sure you have the AWS CLI installed and configured with appropriate permissions.

  1. Open your command-line terminal.
  2. Use the following AWS CLI command to create an IAM role for S3 bucket access. Replace <RoleName> with your desired role name and <AssumeRolePolicyDocument.json> with the name of a JSON file containing your trust policy:
aws iam create-role --role-name <RoleName> --assume-role-policy-document file://<AssumeRolePolicyDocument.json>
For Example:
aws iam create-role --role-name S3BucketAccessRole --assume-role-policy-document file://trust-policy.json

3. After creating the role, you need to attach the desired policies to it. You can do this using the attach-role-policy command. Replace <RoleName> with your role name and <PolicyArn> with the ARN of the policy you want to attach:

aws iam attach-role-policy --role-name <RoleName> --policy-arn <PolicyArn>
For Example:
aws iam attach-role-policy --role-name S3BucketAccessRole --policy-arn arn:aws:iam::aws:policy/AmazonS3FullAccess

4. Your IAM role for S3 bucket access is now created and configured.

Remember to manage IAM roles and policies carefully to ensure security and least privilege access in your AWS environment.

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