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How to use S3 bucket as gem source.

Gem server solutions with their wide feature set, come in very handy for usecases like private hosting, mirroring and inter-release builds. With s3 bucket as your gem source, you get convenience of a private gem server, without the hassle of running or maintaining a host. In this guide, we cover steps required for setting up a private gem source using a s3 bucket and configuration for its use with the gem command.

Please check s3 documentation if you would like to learn about creating a s3 buckets and their pricing.

Make sure you are running on ruby gems version that supports s3 signing. You can update your ruby gems with the following command:

$ gem update --system

Setting up repo

For a static gem source, you will need 4 additional files beside the <gemname>.gem file:

  • specs.<version>.gz
  • latest_specs.<version>.gz
  • prerelease_specs.<version>.gz
  • quick/Marshal.<version>/<gemname>.gemspec.rz

You can generate all of them using one command: gem generate_index.

$ mkdir ~/repo && cd ~/repo

# <gemname>.gem must exist in a directory named `gems`
$ mkdir gems && wget -P gems/

$ gem generate_index --directory .

# replace bucket1 with name of the bucket you created
$ aws s3 sync . s3://bucket1

Use with gem command

It’s good practice to create a separate IAM user with only read rights on the S3 bucket. Use a other IAM user for pushing the gems with write rights.

You can use your s3 source using --source flag:

$ gem install rake -v 12.3.2 --source s3://<AWS_ACCESS_KEY_ID>:<AWS_SECRET_ACCESS_KEY>@bucket1

Use .gemrc if you would like to pre configure multiple s3 sources. It also helps avoid issues related to special characters in the secret key and allows you to specify s3 bucket region.

Add your s3 source under :sources key. Each s3 bucket should have its own set of credentials in a hash under s3_source key. You can use one of the providers to extract AWS credentials:

Or set AWS access id, secret and session token explicitly.

Note that you need to add <path_to_gems_dir>/ to your s3 source uri, if your gem repo doesn’t exist at the root of the bucket. NOTE: The trailing slash.

$ cat ~/.gemrc
- s3://bucket1/
- s3://bucket2/
- s3://bucket3/path_to_gems_dir/
- s3://bucket4/
s3_source: {
  bucket1: {
    provider: "env",
    # region defaults to us-east-1
  bucket2: {
    provider: "instance_profile",
    region: "us-west-2"
  bucket3: {
    id: "AOUEAOEU123123AOEUAO",
    secret: "aodnuhtdao/saeuhto+19283oaehu/asoeu+123h",
    region: "us-east-2"
  bucket4: {
    id: "AOUEAOEU123123AOEUAO",
    secret: "aodnuhtdao/saeuhto+19283oaehu/asoeu+123h",
    security_token: "AQoDYXdzEJr",
    region: "us-west-1"

Read more:

Setting up Travis for inter-release builds