Lab / 5 steps

One CloudFront domain, two S3 buckets.

Requests under /maps/ go to a second bucket, and a Lambda@Edge function strips the prefix so the object keys stay clean.

Lab / One CloudFront domain, two S3 buckets

Step 01 · Console · CloudFront Wrong key on B

Two buckets, two behaviors

One distribution, two origins: /maps/* goes to Bucket B, everything else to Bucket A. Without a rewrite, Bucket B would be asked for a key that starts with maps/.
```
Behavior /maps/*  →  Bucket B
Behavior *        →  Bucket A (default)
```

Step 02 · Lambda · us-east-1 Function ready

Write the rewrite

A Lambda@Edge function in us-east-1 (Node.js 18) removes the /maps prefix from the request URI and logs both versions.

export const handler = async (event) => {
  const request = event.Records[0].cf.request;
  const uri = request.uri;
  console.log('Incoming URI:', uri);

  if (uri.startsWith('/maps/')) {
    request.uri = uri.substring(5); // drop '/maps'
    console.log('Modified URI:', request.uri);
  }
  return request;
};

Step 03 · Lambda · Deploy to Lambda@Edge Deployed

Attach it at Origin Request

Deploy to Lambda@Edge on the /maps/* behavior, at the Origin Request event, so the URI changes just before CloudFront calls Bucket B.
```
Distribution:   your CloudFront distribution
Cache behavior: /maps/*
Event:          Origin Request
Include body:   no
```
Step 04 · Request path 200 from Bucket B

Follow one request

A request for /maps/images/01.jpg matches the /maps/* behavior, the function turns it into /images/01.jpg, and Bucket B serves that object.
```
GET https://example.com/maps/images/01.jpg
  → behavior /maps/*
  → Lambda@Edge: /maps/images/01.jpg → /images/01.jpg
  → s3://bucketB/images/01.jpg
```
Step 05 · CloudWatch Logs Verified

Check the logs

Each run logs the incoming and modified URI to CloudWatch, which is the quickest way to see the rewrite happen.
```
START RequestId: abc123xyz
INFO  Incoming URI: /maps/images/01.jpg
INFO  Modified URI: /images/01.jpg
END RequestId: abc123xyz
```

Read the note: Serve S3 Content from CloudFront with URL Rewrites Using Lambda@Edge All traces

One CloudFront domain, two S3 buckets.

Two buckets, two behaviors

Write the rewrite

Attach it at Origin Request

Follow one request

Check the logs