CloudFront Overview

Overview

CloudFront is a Content Delivery Network (CDN). Anytime you see CDN on the exam, think CloudFront. It improves read performance by caching the content of your website at different edge locations. Because content is cached around the world, users everywhere get lower latency, which improves the user experience.

CloudFront is made of 216 points of presence globally, which correspond to the AWS edge locations around the world. AWS keeps adding locations.

How CloudFront Works

1. Edge locations sit around the world and connect to your origin (an S3 bucket or an HTTP server).
2. A client sends an HTTP request to an edge location.
3. The edge location checks its cache.
4. Cache miss - it goes to the origin to get the result.
5. It stores the result in its local cache.
6. Cache hit - the next client requesting the same content from the same edge location is served without going to the origin.

Example: an S3 bucket and website in Australia, and a user in America. The user requests content from an American edge location using CloudFront, which fetches it from Australia. A second US user requesting the same content is served directly from the edge, not from Australia. A user in China talks to a Chinese point of presence, which is redirected to the S3 bucket, and the content is then cached at that edge.

Origins

With S3 as the origin, the edge location (e.g. Los Angeles, or one serving users in Sao Paulo, Brazil) gets content from the S3 bucket through a private network. The bucket is secured with OAC and by modifying the S3 bucket policy. Content of a bucket in one region is thereby distributed around the world through the points of presence.

CloudFront vs S3 Cross-Region Replication

CloudFront is a CDN that caches content around the world. S3 Cross-Region Replication replicates an entire bucket into another region.

Hands-On Walkthrough

Create the bucket and files

1. Create an S3 bucket (e.g. demo-cloudFront-stephane-V4), leave defaults, click Create bucket.
2. Upload three files: beach, coffee, index.html.
3. Open index.html. The Object URL gives Access Denied (object not public). The Open button works because it generates a pre-signed URL (see S3 Pre-signed URLs). The page shows "I love coffee" and "Hello World" but the image is missing because the image is not public.

Create the distribution

1. Open the CloudFront console. It is a global service with no region selection.
2. Choose the origin domain: your S3 buckets, load balancer, or any domain name including custom HTTP origins.
3. Origin access options: public (bucket must be public, not our case), Origin access control settings (OAC) (recommended), or OAI (the previous way).
4. Click Create control setting (a default name is given) and Create.
5. Leave the bucket policy for now. At this point the bucket policy is empty, so CloudFront cannot read the bucket yet.
6. For WAF, disable the security protections (not needed for the demo).
7. Set the default root object to index.html.
8. Click Create distribution. Creation takes some time.

Update the bucket policy

1. A banner says the S3 bucket policy needs to be updated. Click Copy policy, then use the shortcut to the bucket's policy settings.
2. Click Edit and paste the policy.
3. If you lose the policy, go to Origins -> Edit on the distribution and copy the policy statement from there.
4. The AWS-generated policy allows the CloudFront service principal to do s3:GetObject on any file in the bucket, with a condition that the source is the distribution you created. No other changes are needed.

Test

1. Wait until the distribution status is Deployed.
2. Copy the distribution domain name into a new tab. You see "I love coffee", "Hello World" and the image. /coffee.jpeg and /beach.jpeg also work.
3. Refresh. Content is now served from the CloudFront cache, not S3, and loads much quicker. One request goes to S3 through CloudFront and the rest is cached on the distribution.
4. In the left menu, Origin access lists the origin access controls. The one created is active and assigned to this distribution.

Questions & Answers