Mapping Host Header to custom header for secondary origin

Question

I'm looking for a way to pass the requesting host header onto either the API Gateway or a custom endpoint (outside of amazon) from a cloudfront origin.

Essentially I have multiple domains mapped to a cloudfront catchall and I'm trying to pre-render based off the index request on the server while letting all other resources through.

IF this is not possible, would lambda edge be able to achieve such a thing?

Thanks!

Answer 1

Until such time as Lambda@Edge leaves preview, here's your workaround:

For each domain name, create a separate CloudFront distribution, and add a unique custom origin header.

If you've configured more than one CloudFront distribution to use the same origin, you can specify different custom headers for the origins in each distribution and use the logs for your web server to distinguish between the requests that CloudFront forwards for each distribution.

http://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/forward-custom-headers.html

It should go without saying that "use the logs for your web server" is only one possible use for this value. You can also use it to identify which domain the request is for, by inspecting the inserted request header.

For example, for the site api-42.example.com, add a custom origin header X-Forwarded-Host with the static value the same as the hostname, api-42.example.com.

CloudFront adds the custom origin header to each request when sending it to the origin server.

If the client, for whatever reason, sends the same header, CloudFront discards what the client sent, before adding your header and value to each request.

Since the actual CloudFront distributions themselves are free, there's no real harm in this solution. If you need to create a lot of them, that's easily scripted with aws-cli. By default, accounts can create 200 different distributions, but you can submit a free support request to increase that limit.

You may now be contemplating the impact of this on your cache hit rate, since the different sites wouldn't share a common cache. That's a valid concern, but the impact may not be as substantial as you expect, for a variety of reasons -- not the least of which is that CloudFront's cache is not monolithic. If you have viewers hitting a single distribution but from two different parts of the world, those users are almost certainly connecting to different CloudFront edge locations, thus hitting different cache instances anyway.