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Stemcell Build Status

Stemcell launches instances in EC2. These instances are created to your specification, with knobs like AMI, instance type, and region exposed. The instances are bootstrapped with chef-solo, using a specified git repo and branch as the source of roles and recipes.


Add this line to your application's Gemfile:

gem 'stemcell'

And then execute:

$ bundle

Or install it yourself as:

$ gem install stemcell

Or build the gem locally and install it:

$ gem build stemcell.gemspec
$ gem install ./stemcell-0.4.3.gem


If you're using the command line tool, you'll need to add a stemcell.json to the root of your chef repo. It contains default attributes for launching instances as well as the mapping from backing stores to images. For an example, see examples/stemcell.json.

You should create an RC file for stemcell with your standard options (and place it in the root dir as .stemcellrc?). You can see an example in examples/stemcellrc. As documented in that file, you will need:

  • a mono-repo for chef (like the kind described here)
  • a local checkout of the repo
  • an ssh key that's allowed to read that repo
  • AWS credentials with permission to create instances
  • an AWS ssh key pair
  • an encrypted data bag secret (optional)


Include your base config:

$ source ~/.stemcellrc

Simple launch:

$ stemcell $your_chef_role --git-branch $your_chef_branch

This will cause instance(s) to be launched and their ip's and instance id to be printed to the screen.

More options:

$ stemcell --help

Watching install:

$ stemcell $your_chef_role --tail


To terminate, use the AWS CLI and pass a space separated list of instance ids:

$ aws ec2 terminate-instances --instance-ids i-12345678 i-12345679 i-12345670


This README presents stemcell as a tool for administrators to use to create instances. However, we designed stemcell to be easily useful for automated systems which control server infrastructure. These automated systems can call out to stemcell on the command-line or use the ruby classes directly.

Similar Tools

There are a few additional tools which bootstrap EC2 instances with chef-solo. If you're using chef-server, obvious answer is knife-ec2. Unless you're working on a big team where lots of people edit cookbooks simultaneously, we strongly recommend this approach! It's especially excellent when paired with hosted chef, which makes getting off the ground with configuration management fast and easy.

If you want to use knife-ec2 with chef-solo, you could use knife solo. Another approach which is great for interactive usage involves using fabric to bootstrap chef(with gist).

Finally, we couldn't resist doing a bit of code archeology. People have been using chef with EC2 for a long time! One early article is this one, which isn't even on the web anymore. However, it's spawned some recently-active tools like this and this. Similar approaches are mentioned here, with code here or here (with accompanying blog post) This article, also mentions many worthwhile predecessors.