I read this:
"I can't use this until I can serve my root domain without redirection to "www". Can Amazon designate an IP address (or set of IP addresses) for S3 that I can point my root A record to?"
Is it still true that I need to have a domain host just as a proxy to S3 and setup CNAME to point a subdomain to S3 bucket? And there is no better way?
There are no better ways, only most costly ways.
You can set up an EC2 image with a proxy, and allow the proxy to access S3 on your behalf, while accessing the remainder of your web site somewhere else. Since scalability is a concern of yours, you'll also want to use the automatic scaling tools for EC2 as access to your proxy grows.
Or, just re-architect your application to use the CNAME-based approach for all content located in S3.
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