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Last pushed: 4 months ago
Short Description
Publish NPM packages to S3 with correct caching headers and sensible update behaviour.
Full Description


This is a tool to publish an NPM package to an Amazon S3 bucket using
sensible defaults. It assumes that:

  • you are releasing prebuilt assets in your NPM package
  • you wish to expose the entirety of your package in the S3 bucket for each
    released version

It will be most useful only if you also:

  • define a main entrypoint in your package's package.json
  • ensure your entrypoint file is capable of loading the remainder of your
    packages assets as necessary from the bucket HTTP URL (or CDN URL)

To be explicit, this means that you will probably need your entrypoint script

  1. Know what version of your package it is from.
  2. Know the URL at which your bucket can be accessed over HTTP.
  3. Manage the loading of the rest of your application using 1, 2, and the URL
    conventions described below.


Why would you use this? Because:

  1. You publish a JavaScript application that you want developers to be able to
    include on their site using a single tag such as:
    <script src=""></script>
  2. You want to take advantage of HTTP/2 request multiplexing to load the various
    assets that make up your application (i.e. you don't want to have to bundle
    your entire application into a single file).
  3. You want to be certain that when you release a new version of the package,
    that release is observed as "atomic" by your users. There should be no
    possibility of a user's browser loading half of the assets from the new
    version and half from the old version.
  4. You want to make best possible use of CDN and browser caches when delivering
    your application to users.

This tool enables a release process that satisfies all of the above by releasing
the majority of your package to versioned URLs with caching headers that
indicate the content is immutable.

Efficient releasing of new versions is made possible by aliasing a package
"entrypoint" script with a short cache TTL. This entrypoint script is
responsible for loading the rest of your application.


docker run --rm \
  -e AWS_ACCESS_KEY_ID=... \
  nickstenning/s3-npm-publish <pkgname> <s3path>

For example, if you were releasing the mypkg package:

docker run --rm \
  -e AWS_ACCESS_KEY_ID=... \
  nickstenning/s3-npm-publish mypkg s3://

See the "Example scenario" below to understand how s3-npm-publish lays out
files in your bucket.

To release a specific version of a package (any NPM version identifier will

docker run --rm \
  -e AWS_ACCESS_KEY_ID=... \
  nickstenning/s3-npm-publish mypkg@2.0.1 s3://

To release to a path other than the bucket root:

docker run --rm \
  -e AWS_ACCESS_KEY_ID=... \
  nickstenning/s3-npm-publish mypkg s3://

If you are running in an environment where the AWS CLI tools will be able to
obtain credentials without you explicitly providing them (for example on an EC2
instance with an appropriate instance role profile) you can omit the AWS_*
environment variables:

docker run --rm nickstenning/s3-npm-publish mypkg s3://

Example scenario

You have a package, giraffejs, which contains a JavaScript application which
you intend to release to an S3 bucket, s3:// The package
contains the following assets:


First you would release the giraffejs package to NPM as usual, and then you
would run s3-npm-publish as follows:

docker run --rm \
  -e AWS_ACCESS_KEY_ID=... \
  nickstenning/s3-npm-publish giraffejs s3://

This automatically detects that the latest version of the giraffejs package is
(for example) 1.2.3 and will upload the contents of the package to:


Each of these files will be served with HTTP Cache-Control headers which
ensure that they essentially never expire from any cache:

Cache-Control: public, max-age=315360000, immutable

If package.json contains a main key, the file to which it points will be
used to set up aliases in the bucket. For example if package.json contains

  "main": "./index.js",

then s3-npm-publish will upload index.js to


The first of these (with the full version number) will be served with similar
Cache-Control headers to the rest of the package. The latter three (which may
be updated when a new version is released) are served with a much shorter TTL
and a request to user agents to revalidate the resource if the cache entry goes

Cache-Control: public, max-age=1800, must-revalidate

This allow you to easily publish new versions of your package, and clients
pointing to (for example) the 1.2 alias will receive the new entrypoint script
when a new version of the package in the 1.2.X series is released.

Unsolicited advice

If you are serving a JavaScript application from an S3 bucket, you should
probably set up a CloudFront distribution or other CDN to front your bucket.
This will improve the perceived loading speed of your package assets, and (if
you have substantial traffic) likely reduce your costs.


This project is released under the MIT license, a copy of which is provided in

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