Access Control Methods Overview
Bucket Policies vs. IAM
Bucket Policies
Resource-based policies defined at the bucket level.
Can explicitly allow or deny access to specific principals.
Takes precedence over other permissions.
Applied to all objects or a subset within the bucket.
Defined directly on the bucket resource.
IAM (Identity and Access Management)
Identity-based policies.
Grants temporary permissions through roles.
Can be assigned to users, services, or applications.
Manageable through AWS Console or SDK.
Access keys automatically rotate for enhanced security.
Permission Evaluation Process
Single Account Access
Bucket Policy Check:
Explicit deny: Access blocked.
Explicit allow: Access granted regardless of IAM permissions.
Neither: Proceeds to IAM check.
IAM Permission Check:
Evaluates user's IAM policies.
Checks group memberships.
Verifies role permissions.
Cross-Account Access
Source Account Requirements:
Create role with appropriate permissions.
Establish trust policy allowing external account access.
Destination Account Requirements:
Create role to assume the source account's role.
Grant necessary permissions to principals.
Permission Flow:
Principal assumes local role.
Local role assumes cross-account role.
Access granted based on cross-account role permissions.
Networking Considerations
Access Methods
Public Internet Access:
Via Internet Gateway.
Higher data transfer costs.
Standard internet latency.
S3 Gateway Endpoint:
Uses AWS private network.
Lower data transfer costs.
Reduced latency.
Requires VPC route table configuration.
Uses Elastic Network Interface.
Best Practices and Key Considerations
Security
Prefer IAM roles over bucket policies for cross-account access.
Take advantage of automatic key rotation with IAM roles.
Use explicit denies in bucket policies for critical restrictions.
Networking
Implement S3 gateway endpoints for cost-effective internal access.
Configure appropriate route tables for VPC connectivity.
Consider data transfer costs when choosing access methods.
Access Management
Clearly define trust relationships for cross-account access.
Use temporary credentials through IAM roles when possible.
Maintain principle of least privilege.
Regular audit of access patterns and permissions.
Implementation Examples
Principal Types That Can Assume Roles
IAM Users.
EC2 Instances.
Lambda Functions.
Custom Applications.
Network Configuration
This configuration provides:
Private network access.
Reduced costs.
Improved latency.
Secure communication path.
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