CloudFront Indexes

July 18, 2016

Some of us are vain enough to want to be able to use extensionless filenames when hosting a static site through CloudFront. I previously wrote about a workaround that can be used to achieve this effect by stripping a file’s extension and forcing its content type when uploading to S3. I now realize that this is about half the solution; it does get us extensionless URLs, but doesn’t handle all the edge cases around indexes.

If I have a blog and want my articles to have URLs like /articles/my-article, then it stands to reason that I might also want an index of all my articles at /articles. If you’re building your static content locally and then syncing it up to S3 using aws s3 sync, you can’t have both a file called articles (the index) and a directory called articles (the container for articles) on your filesystem. In other words, this isn’t allowed:

filesystem/
  - articles
  + articles/
    - my-article

This might present us with a big problem, except that S3 is not a filesystem, it’s a key/value store wherein we occasionally pretend that keys containing slashes are a nested hierarchy of directories. So although not kosher on a filesystem, this layout is perfectly okay on S3:

s3-bucket/
  - articles
  - articles/my-articles

Thus solving the problem above of having an index and container with the same name.

Publishing the site isn’t quite as trivial as running aws s3 sync anymore, but can still be made easy by uploading in two passes:

  1. Sync all non-index pages with aws s3 sync.
  2. Upload all index pages with aws s3 cp after correcting their path name.

I generate index files locally with an HTML extension so that they’re more discoverable if I point web servers at the directory; they’ll often know how to handle files named index.html by default (like say Go’s http.FileServer). So our final local directory structure looks like this:

filesystem/
  - index.html
  + articles/
    - index.html
    - my-article

Below are a few slightly convoluted shell commands to do the upload. The last step iterates a content directory called public, finds any files named index.html, and uploads them to S3 as the name their parent directory them (e.g. articles/index.html becomes articles):

# Step 1: HTML
aws s3 kync ./public/ s3://$S3_BUCKET/ --acl public-read --content-type text/html --delete --exclude 'assets*'

# Step 2: Assets (CSS, images, JS)
aws s3 sync ./public/assets/ s3://$S3_BUCKET/assets/ --acl public-read --delete

# Step 3: HTML index files
find ./public -name index.html | egrep -v './public/index.html' | sed "s|^\./public/||" | xargs -I{} -n1 dirname {} | xargs -I{} -n1 aws s3 cp ./public/{}/index.html s3://$S3_BUCKET/{} --acl public-read --content-type text/html

There is also one finishing touch to be made: the system described here will handle all index files except the one at the very top-level, which we cannot upload with a name like /. Luckily CloudFront has provided a workaround by allowing us to configure a Default Root Object, which is the name of the file to serve from the distribution’s root. Configure it to index.html, make sure that a corresponding object gets synced to the S3 bucket, and you’re done.

CloudFront Indexes was published on July 18, 2016.

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