CloudFront & Caching Layers

CloudFront & Caching Layers

Step 1 of 10

The origin lives in one Region. Viewers are everywhere, so CloudFront puts caches in edge locations near them.

The Idea

CloudFront answers viewers from edge locations near them. A miss asks a regional edge cache, then the origin — S3, a load balancer, any HTTP server. The cache policy sets the cache key (which headers, cookies and query strings make two requests "the same") and TTL bounds; within them, the origin's Cache-Control headers decide how long a copy lives.

Real-World Example

A web app names its JavaScript bundles by content hash, caches them for a year and never invalidates them: a deploy ships new names. Origin access control keeps the S3 bucket readable only by the distribution.

The Tradeoff

A bigger cache key means fewer hits. Invalidations remove paths from the caches, but paths beyond a monthly free allowance are billed; versioned file names avoid them entirely.

Hands-On

# illustrative — bucket and distribution ID are placeholders
aws s3 cp app.3f9a1c.js s3://site-bucket/js/ \
  --cache-control "public, max-age=31536000, immutable"
aws cloudfront create-invalidation --distribution-id E2EXAMPLE \
  --paths "/index.html" "/css/*"

Your turn

Put the steps in the right order.

1. 1The origin returns the object with a Cache-Control header↑↓
2. 2Both cache layers keep a copy; later requests are hits↑↓
3. 3A viewer requests /app.js from the nearest edge location↑↓
4. 4The edge misses and asks the regional edge cache, which misses too↑↓

Check order

Mini quiz

1 / 3

Putting every cookie and query string into the cache key:

• ARaises the hit rate
• BLowers the hit rate — near-identical requests become different objects
• CHas no effect
• DMakes the content private

Sources

• How CloudFront delivers content — Amazon CloudFront Developer Guide
• Manage how long content stays in the cache — Amazon CloudFront Developer Guide
• Invalidate files to remove content — Amazon CloudFront Developer Guide
• Restrict access to an Amazon S3 origin — Amazon CloudFront Developer Guide