AWS CloudFront Caching Explained for Beginners

Website and application users expect fast load times, no matter where they are in the world. Slow delivery of content affects user experience, conversions, and search rankings. Amazon CloudFront, AWS’s Content Delivery Network (CDN), helps solve this by caching content close to users for faster delivery.

If you are new to CloudFront or CDN caching, this guide will help you understand the basics of how caching works, key configuration settings, and how to optimize performance.

What Is AWS CloudFront?

Amazon CloudFront is a Content Delivery Network (CDN) that distributes content to users through a global network of edge locations. Instead of serving content directly from the origin (like S3, EC2, or an on-prem server), CloudFront caches it at edge locations, reducing latency and improving load time.

How CloudFront Caching Works

When a user requests a file from your application, CloudFront follows a caching workflow:

1. User sends request

   • The user requests a resource, such as an image, CSS file, video, or API response.

2. CloudFront checks the cache at the nearest edge location

   • If the content is already cached (cache hit), CloudFront returns it immediately.

3. If not cached (cache miss)

   • CloudFront forwards the request to the origin to fetch the content.

4. CloudFront caches the response

   • The content is stored in the edge cache for future requests.

5. Subsequent users nearby get faster delivery

   • Future requests for the same content from that region are served instantly.

Key CloudFront Caching Terms

Edge Location

Physical data centers across the world that cache and serve content to users.

TTL (Time to Live)

Determines how long CloudFront should store cached content at an edge location. It can be set using:

• Minimum TTL

• Maximum TTL

• Default TTL

Cache Hit and Cache Miss

• Cache Hit: Content is found in CloudFront’s cache.

• Cache Miss: Content is not found, so CloudFront retrieves it from the origin.

Cache Behavior

Rules that define how CloudFront handles different types of requests. For example, you can set caching differently for:

• Static assets (images, scripts)

• API responses

• Admin or dynamic pages

What Can Be Cached in CloudFront?

How TTL Affects Caching

TTL controls how long content stays in cache before CloudFront revalidates with the origin.

Example:

• Static assets (images, CSS): TTL 1 day to 1 year

• Dynamic content (HTML, API): TTL from a few seconds to minutes

Cache Invalidation

Sometimes you need to remove or refresh cached content, such as after a website update. CloudFront provides cache invalidation, which removes objects from the cache before the TTL expires.

Example invalidation patterns:

• /* removes everything

• /images/* removes all images

• /index.html removes a specific file

Note: CloudFront offers a number of free invalidation requests per month; extra requests incur cost.

How to Improve CloudFront Cache Hit Ratio

A high cache hit ratio means fewer requests go to the origin, reducing latency and AWS costs.

Tips to improve hit ratio:

1. Set longer TTL for static assets

2. Enable origin shield for improved caching efficiency

3. Remove unnecessary query strings from cache keys

4. Compress and version static files

5. Use Cache Policies and Origin Request Policies wisely

Cache Policies in CloudFront

Amazon provides predefined policies, or you can create your own. The cache key determines what CloudFront uses to identify cached content.

Cache key components can include:

• URL path

• Query strings

• Cookies

• Headers

For beginners, AWS recommends using:

• CachingOptimized for static content

• Elemental-MediaPackage for streaming content

Benefits of CloudFront Caching

Real-World Example

If your website hosts images on S3 and users from India request them, without CloudFront, the request goes to the S3 bucket region, possibly in the US or Europe. With CloudFront, the image is cached at an edge location in Mumbai, reducing delay and speeding up image load time dramatically.

Conclusion

CloudFront caching is a powerful way to improve performance, reduce latency, and reduce infrastructure costs. Understanding how caching works and configuring TTLs, cache behaviors, and invalidations correctly can significantly enhance your application’s speed and efficiency.

Whether you are building a website, streaming media, or deploying a global web application, CloudFront helps deliver content reliably and quickly to users anywhere in the world.