CloudFront Origin Access Control (OAC) is a security feature that restricts access to your origin content, ensuring that users can only access your content through CloudFront distributions rather than accessing the origin server directly. This is particularly important when using Amazon S3 buckets …CloudFront Origin Access Control (OAC) is a security feature that restricts access to your origin content, ensuring that users can only access your content through CloudFront distributions rather than accessing the origin server directly. This is particularly important when using Amazon S3 buckets or Application Load Balancers as origins.
OAC is the recommended method for securing S3 origins, replacing the legacy Origin Access Identity (OAI). When configured, CloudFront signs all requests to your origin using AWS Signature Version 4 (SigV4), providing enhanced security and supporting additional use cases like server-side encryption with AWS KMS.
Key benefits of Origin Access Control include:
1. **Enhanced Security**: OAC supports all S3 buckets in all AWS Regions, including buckets that use SSE-KMS encryption. It also supports dynamic requests (PUT and DELETE) to S3.
2. **Credential Management**: AWS handles the signing credentials automatically, rotating them frequently for improved security.
3. **Granular Permissions**: You can configure specific bucket policies that allow only your CloudFront distribution to access the content.
To implement OAC, you need to:
- Create an Origin Access Control in the CloudFront console
- Associate it with your distribution and specify the S3 origin
- Update your S3 bucket policy to grant the CloudFront service principal permission to access objects
The bucket policy must include a condition that verifies the request comes from your specific CloudFront distribution using the AWS:SourceArn condition key.
OAC also supports requiring HTTPS between CloudFront and your origin, adding another layer of security. For SysOps Administrators, understanding OAC is essential for implementing secure content delivery architectures and ensuring compliance with security best practices while maintaining optimal performance through CloudFront edge locations.
CloudFront Origin Access Control (OAC)
What is CloudFront Origin Access Control?
CloudFront Origin Access Control (OAC) is a security feature that restricts access to your Amazon S3 bucket origins so that content can only be accessed through your CloudFront distribution. OAC is the recommended successor to Origin Access Identity (OAI) and provides enhanced security capabilities.
Why is Origin Access Control Important?
OAC is crucial for several reasons:
• Security: Prevents users from bypassing CloudFront and accessing S3 content via S3 URLs • Cost Control: Ensures all requests go through CloudFront, enabling proper caching and reducing S3 request costs • Access Logging: All access is logged through CloudFront for better auditing • Enhanced Encryption: OAC supports S3 server-side encryption with AWS KMS (SSE-KMS) • All S3 Regions: OAC works with S3 buckets in all AWS Regions, including newer regions
How Origin Access Control Works
1. Create an OAC in CloudFront and associate it with your distribution 2. Update S3 bucket policy to allow access from the CloudFront service principal 3. CloudFront signs requests using SigV4 (Signature Version 4) before sending them to S3 4. S3 validates the signature and allows access only from authorized CloudFront distributions 5. Users cannot access S3 content using S3 URLs; they must use CloudFront URLs
OAC vs OAI (Origin Access Identity)
OAC is the newer and recommended approach:
• OAC supports SSE-KMS encryption while OAI does not • OAC uses IAM service principals for better security • OAC supports dynamic requests (PUT, POST, DELETE) to S3 • OAC works with all AWS Regions • OAI is considered legacy but still functional
Configuring Origin Access Control
Step 1: Create an OAC in CloudFront console Step 2: Associate OAC with your S3 origin in the distribution Step 3: Update S3 bucket policy with the provided policy statement Step 4: Block public access on the S3 bucket
S3 Bucket Policy Example for OAC:
The policy grants s3:GetObject permission to the CloudFront service principal (cloudfront.amazonaws.com) with a condition that validates the distribution ARN.
Exam Tips: Answering Questions on CloudFront Origin Access Control
• When a question asks about restricting S3 access to CloudFront only, think OAC or OAI • If the scenario involves SSE-KMS encryption with CloudFront and S3, OAC is the answer (OAI does not support KMS) • Questions mentioning legacy or older configurations may refer to OAI • OAC is the recommended solution for new implementations • Remember that OAC uses SigV4 signing for authentication • If asked about preventing S3 URL access while allowing CloudFront access, OAC is the solution • OAC requires updating the S3 bucket policy to trust the CloudFront service principal • Know that Block Public Access should be enabled on S3 buckets when using OAC • Questions about uploading files through CloudFront to S3 require OAC (OAI only supports GET requests) • If a question mentions newer AWS Regions and S3 origin access, OAC is required