Last updated February 15, 2022

Amazon Simple Storage Service (S3) is a durable and available store, ideal for storing application content like media files, static assets, and user uploads.

Storing static files elsewhere is crucial for Heroku apps since dynos have an ephemeral filesystem. Whenever you replace a dyno or when it restarts, which happens daily, all files that aren’t part of your application’s slug are lost. Use a storage solution like S3 to offload the storage of static files from your app.

Overview

All files sent to S3 get stored in a bucket. Buckets act as a top-level container, much like a directory, and its name must be unique across all of S3. A single bucket typically stores the files, assets, and uploads for an application. An Access Key ID and a Secret Access Key govern access to the S3 API.

Setting Up S3 for Your Heroku App

Enabling an application to use S3 requires that the application have access to your AWS credentials and the name of the bucket to store files.

Configure Credentials

You can find your S3 credentials in My Security Credentials section of AWS.

Use the heroku config:set to set both keys:

$ heroku config:set AWS_ACCESS_KEY_ID=MY-ACCESS-ID AWS_SECRET_ACCESS_KEY=MY-ACCESS-KEY
Adding config vars and restarting app... done, v21
  AWS_ACCESS_KEY_ID     => MY-ACCESS-ID
  AWS_SECRET_ACCESS_KEY => MY-ACCESS-KEY

Name Your Bucket

To create a bucket, access the S3 section of the AWS Management Console and create a new bucket in the US Standard region:

Follow AWS’ bucket naming rules to ensure maximum interoperability.

Store the bucket name in a config var to give your application access to its value:

$ heroku config:set S3_BUCKET_NAME=example-app-assets
Adding config vars and restarting app... done, v22
  S3_BUCKET_NAME     => example-app-assets

Manually Uploading Static Assets

You can manually add static assets such as videos, PDFs, Javascript, CSS, and image files using the command line or the Amazon S3 console.

Uploading Files From a Heroku App

There are two approaches to processing and storing file uploads from a Heroku app to S3: direct and pass-through. See the language guides for specific instructions.

Direct Uploads

In a direct upload, a file uploads to your S3 bucket from a user’s browser, without first passing through your app. Although this method reduces the amount of processing your application needs to perform, it can be more complex to implement. It also limits the ability to modify files before storing them in S3.

Pass-Through Uploads

In a pass-through upload, a file uploads to your app, which in turn uploads it to S3. This method enables you to perform preprocessing on user uploads before you push them to S3. Depending on your chosen language and framework, this method can cause latency issues for other requests while the upload takes place. Use background workers to process uploads to free up your app.

Language-Specific Guides

Here are language-specific guides to handling uploads to S3:

Referring to Your Assets

You can use your assets’ public URLs, such as http://s3.amazonaws.com/bucketname/filename, in your application’s code. S3 directly serves these files, freeing up your application to serve only dynamic requests.

For faster page loads, consider using a content delivery service, such as Amazon Cloudfront to serve your static assets instead.