CloudFront Signed URL vs S3 Pre Signed URL - When to Use What?

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IN TODAY'S EDITION

🧠 Use Case

• CloudFront Signed URL vs S3 Pre Signed URL - When to Use What?

🚀 Top News

• AWS PrivateLink now supports cross-region connectivity

  With this update, customers can now use Interface endpoints to access VPC endpoint services across different AWS Regions within the same AWS partition.

👀 Remote Jobs

• VRCHAT is hiring a DevSecOps Engineer

  Remote Location: Worldwide

• Lighthouse Tech is hiring a AWS Cloud Engineer

  Remote Location: Worldwide

📚️ Resources

• Git Flops: The Dangers of Terraform Automation Platforms

  Terraform automation platforms, like Terraform Cloud and Atlantis, are vulnerable to attacks through malicious HCL in speculative terraform plan operations, risking cloud credential exposure.

• How to use CloudTrail to analyse your CloudWatch API Usage

  By combining CloudTrail with CloudWatch Log Insights or Athena, teams can gain visibility into usage patterns, optimize spend, and enhance observability.

• Spin up a local Kubernetes environment with Kind and Cilium without kube-proxy

  This lightweight setup enables efficient testing and development with enhanced observability through Hubble.

🛠️ TOOL OF THE DAY

Trailscraper -  A command-line tool to get valuable information out of AWS CloudTrail. A general purpose toolbox for working with IAM policies.

🧠 USE CASE

CloudFront Signed URL vs S3 Pre Signed URL - When to Use What?

Let’s say you’re rolling out a new application to global beta testers. Your files are stored in S3, but testers need fast, reliable access with strict expiration controls and optional geographic restrictions.

Do you use CloudFront Signed URLs or S3 Pre-Signed URLs?

At first glance, both solve the same problem: granting temporary, secure access to content.

However, their approach and flexibility differ.

If I have to simplify:

CloudFront Signed URL

• Designed for accessing content through CloudFront (e.g., S3, custom origins).

• Uses account-wide key-pairs, manageable only by the root user.

• Offers advanced filters: IP restrictions, path control, expiration, date limits, and more.

• Leverages CloudFront’s caching and edge locations for low-latency.

S3 Pre Signed URL

• Provides direct access to a specific S3 object, acting as the user who signed it.

• Utilizes IAM credentials of the user or application issuing the request.

• Limited to the permissions of the signing IAM principal, with a short lifespan.

How It Works ?

CloudFront Signed URL Workflow

• The client requests content that resides behind CloudFront.

• CloudFront verifies the signed URL and fetches the content from its cache or the origin (e.g., an M5 instance or S3 bucket).

• The client gets the content, benefiting from edge delivery and low latency.

S3 Pre Signed URL Workflow

• Your application generates a pre-signed URL using AWS SDKs or a simple Lambda function.

• The client uses the pre-signed URL to interact directly with the S3 bucket.

• The URL expires after a specified duration, ensuring secure and time-bound access.

How to Revoke a Signed URL ?

CloudFront Signed URL

1. Invalidate CloudFront Cache

aws cloudfront create-invalidation --distribution-id <distribution-id> --paths "/<path-to-object>"

2. Remove the active key pair used to generate the signed URL

aws cloudfront delete-public-key --id <key-id>

3. Replace it with a new key pair for future URLs

S3 Pre Signed URL

1. Remove public read/write access for the specific object.

2. Set the object ACL

aws s3api put-object-acl --bucket <bucket-name> --key <object-key> --acl private

3. Rotating the associated IAM access keys.

Security Best Practices

CloudFront Signed URLs:

• Rotate signing keys periodically.

• Configure cache behaviors and origin access identities for added security.

• Use HTTPS for content delivery.

S3 Pre-Signed URLs:

• Use IAM policies with the least privileges.

• Set short expiration times (ExpiresIn) to minimize risk.

• Monitor access using S3 access logs or CloudTrail.

When to Use What?

• Use CloudFront Signed URLs for securing content from custom origins or advanced scenarios requiring IP whitelisting, georestrictions, or time-limited access to multiple resources via a custom policy.

• Use S3 Presigned URLs for direct access to specific S3 objects, with precise control over operations (GET, PUT, or DELETE) and expiration time.

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