CNAME auto-generation can break CDN fronted sites

[davidski]

The improved build_cname() functionality included with V1.2.0 causes me a bit of grief with my deployment architecture.

I have a GitHub hosted site (davidski.github.io/evaluator) that is fronted by AWS CloudFront at evaluator.severski.net. I need to put https://evaluator.severski.net into my _pkgdown.yml for links to be generated correctly for the canonical form of my site. With this in the URL field, pkgdown generates a CNAME which, if deployed, causes an infinite loop between my CDN and my origin site.

I'm able to work around this by putting the CNAME file into my .gitignore, but I wonder if there isn't a more elegant solution for this.

[hadley]

I wonder if build_cname() should be moved out of init_site() and into one of the deploy functions, since it's specifically concerned with deployment via github pages.

[hadley]

Maybe we should have to deploy_to_github_pages() which would be a thin wrapper around build_cname() + deploy_to_branch()