prerender.io cloudfront example middleware

This is an example of integrating prerender.io and a SPA in S3 served over Cloudfront.

Instructions

1. Upload prerender-cloudfront.yaml to Cloudformation as a new stack, that'll setup the example for you. Enter your prerender.io token when asked.
2. Upload code.js and index.html to the S3 bucket created by Cloudformation in step 1.
3. Change the read permissions for code.js and index.html to be publicly readable.

Testing

To see the page as rendered by prerender.io run:

curl -H 'User-Agent: Facebot' https://${CLOUDFRONT_DOMAIN}/over/here

The same page without pre-rendering:

curl https://${CLOUDFRONT_DOMAIN}/over/here

Implementation

Two Lambda@edge functions are used. The first detects bot requests on requests entering the system, it sets a header which Cloudfront uses to partition the cache. The second function, run after the cache, detects the presence of the header and, if present, routes the request to Prerender.io

Caching

By default, static resources from the bucket are cached for a long time period. This improves performance but means that the deploy process of any real app will need a Cloudfront purge step.

As prerender.io does NOT want any Cloudfront caching (see https://github.com/prerender/prerender/issues/93#issuecomment-366774910) we disable that by including a X-Prerender-Cachebuster header which effectively disables cloudfront caching.

NOTE: using X-Prerender-Cachebuster is probably not optimal, if you find a better way, please let me know.