A CLI for building, managing, and deploying slugs.
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Slugforge is a tool used at Tapjoy to build, manage, and deploy slugs of code for any project that conforms to a basic structure defined below. The idea is to have a file that conforms to the "build" part of a 12 factor app. We built this tool after looking at a number of options in the open source community, but not finding anything that met all of our needs. After building and using this tool over the past year we now want to share that work with the world so that others can benefit for them as well.

A slug is a single file that contains all application code, build artifacts, and dependent binaries necessary to run the application. This would include bundled gems for a ruby app, or jars for a java app. As per the outlines laid out for a 12 factor app, the slug does not include any configuration for the app. All configuration should be specified as environment variables, which the app should recognize and which are specified outside of the slug. In practice the slug could be used to deploy the application for a development, testing, qa, or production server, each of which only differ in their configuration.


Developers should install slugforge locally to assist with building, managing, and deploying slugs. After following the installations below, you can confirm that slugforge is properly installed by typing slugforge and ensuring that the help is displayed.

Installing from source

If you are assisting with the development of Slugforge, or if the installation cannot be completed using the gem files in Gemfury, you can clone the repositories and build the gems from their source.

  1. Ensure that you are using an appropriate Ruby (like 1.9.3-p484), if necessary:

     rvm use 1.9.3-p484
  2. Install the Tapjoy customized version of FPM:

     git clone git@github.com:Tapjoy/fpm.git
     cd fpm
     gem build fpm.gemspec
     gem install fpm*.gem --no-ri --no-rdoc
     cd ..
  3. Install the slugforge gem:

     git clone git@github.com:Tapjoy/slugforge.git
     cd slugforge
     gem build slugforge.gemspec
     gem install slugforge*.gem --no-ri --no-rdoc
     cd ..


Configuring settings

There are a few settings that need to be configured for certain functionality to be available. These can be configured in the environment, on the command-line, or in a configuration file.

AWS configuration

In order to store, retrieve, or query files in S3 buckets, or to be able to specify servers to deploy to by their instance ID, you need to configure your AWS access key and secret access key. As most developers will need these for other tools, we recommend setting the variables in your environment variables:

export AWS_ACCESS_KEY_ID=<20 character access key>
export AWS_SECRET_ACCESS_KEY=<40 character secret access key>

In addition to you AWS keys, Slugforge needs to know what bucket in S3 you will be using to store your slugs. This can be specified in your configuration file, environment, or on the command line:

  • Slugforge configuration file

Add the following setting to your configuration file:

  slug_bucket: <bucket_name>
  • Environment variable:

      export SLUG_BUCKET=<bucket_name>
  • Command-line parameter:


SSH configuration

When deploying a slug to a host, the Slugforge tool with create a SSH connection to that host. It will first try a username specified on the command line, or in your configuration files. If that is not specified, it will look at your standard SSH configuration for a username. If all that fails, it will use your current username. If that account does not have access to log into the remote host you should override the default:

export SSH_USERNAME=<username>

Typical developer workflow

Once a developer has finished making their changes and have tested them locally, they are generally interested in deploying them to some test environment so that they can test them in a more production-like environment. Slugforge helps automate that process, making it simple and repeatable.

Build a slug with the command line tools

NOTE: If any gems are used that include native extensions, the slug must be built on the same architecture as it will be deployed to.

In certain circumstances, it may be useful to build your slug locally. A local slug can generally be built from the project's root directoy by running the following command:

slugforge build --ruby 1.9.3-p194

This will create a new slug in the current directory. While specifying the ruby version is optional, the above recommended value is currently appropriate in most cases.

Tagging your slugs (recommended)

Slugs can be tagged with names, such as the deployment that they are associated with. To tag a slug on S3 for myproject as stable, do the following:

slugforge tag set stable <slug_name> --project myproject

You can tag any slug using a portion of its name. This can be any sequential subset of characters, as long as it uniquely identifies the slug. To tag a specific slug for the current project as test, do the following:

  1. Determine the name of the slug

     slugforge wrangler list
  2. Create the test tag for the slug using a unique portion of the slug name. Assuming that the slug name was myproject-20130909201513-8b81b614d3.slug, you might use:

     slugforge tag set test 0909201513

Deploying your slugs

Now that you have your slug, and have a way of referencing it, it's time to deploy your slug for testing. The most convenient ways of deploying is by tag. You can optionally pass a list of servers to deploy to, rather than a single server. In addition, if you are in the local repository for a project, the --project option is optional.

When specifying the hosts to a deploy to, there are a number of ways to target them. The different types can be intermixed and will all be OR'ed together to determine the list of target machines:

  • IP Addresses: four numbers, joined with dots (eg.
  • Host name: a series of words, joined with dots (eg. ec2-123-45-6-78.compute-1.amazonaws.com)
  • EC2 instance: an AWS instance name (eg. i-0112358d)
  • AWS tag: an AWS tag name and value, joined with equals (eg. cluster=watcher)
  • Security group: an AWS security group name (eg. connect-19)

NOTE: When using instance names, tags, or security groups, you need to be using an AWS access key and secret key that have permissions to view those resources. This can create conflicts if the S3 bucket that you want to access is using a different pair of keys.

Deploying by tag name

Assuming that you wanted to deploy the stable release of myproject to the host at, you would execute:

slugforge deploy tag stable --project myproject

Deploying local slug files

If you had built your slug locally, you can deploy the file directly from your local machine. To deploy a file in the current directory called filename.slug to server, and install it as myproject, you would execute:

slugforge deploy file filename.slug --project myproject

Repository format

The repository used to create a slug need only have a few required parts.


The slug will create upstart services when installing the slug based on the lines in the Procfile at the root of the repository. This is exactly the same format as a Heroku/Foreman Procfile. Each line will be converted to an upstart service which will monitor the lifecycle of each of the apps processes.

"build" script

The contents of the slug will be the entire repository directory contents, minus the .git, log, and tmp directories, in whatever state its in after running a script found in deploy/build. This script can be written in any language and perform any tasks but it should put the repository in the necessary state for packaging such that all processes defined in the Procfile will run successfully. That means that any binaries specified in the Procfile should be created, compiled, downloaded, materialized, conjured etc. All dependent packages or binaries should be placed in the repository. For example, a ruby project might want to call bundle install --paths vendor/bundle in order to package all necessary gems for runtime execution.

If no deploy/build script exists in your repository, no prepackage build steps will be taken.

Install behavior customization

If your slug requires extra fancy post install setup, you can configure that by adding scripts in the deploy directory at the root of your repo. slugforge will look for a subset of the scripts run by the chef deploy_revision resource. It will run deploy/before_restart and deploy/after_restart at the times you would expect when originally starting or restarting the upstart services associated with the app.

This sort of customization should only be app specific and very minimal. All prerequisite OS configuration and slug install should be managed by a tool like chef or puppet, or baked directly into the AMI.

The slug itself

The slug will be a .slug package which contains the state of the app repo after the build script has run as well as the upstart scripts generated by this tool. That's it. El fin. The files will be installed on the server in /opt/apps/<app-name> where app-name is configured at deploy time defaulting to the name of the directory containing the repo.

Slug storage

Slugs will be stored in S3 and downloaded to servers on deploy. The S3 bucket will have project directories which contain the slugs for any given project. The name of the slug will follow the format


For example



From a single server's point of view, in order to deploy a new slug to a server run the command

curl http://s3.amazonaws.com/slugs/<project_name>/<slug_name>.slug && <slug_name>.slug -r -i <deploy_path>

The deploy scripts we use to deploy clusters will coordinate which slug is installed on each server to allow for isolated deploys, incremental rollout, rollback etc. The most recently installed slugs will be cached in /tmp on a server to allow for fast rollback.

On installation the upstart scripts will be installed in /etc/init and started or restarted.

Unicorn/Rainbows support

Slugs have special handling for unicorn and rainbows to correctly handle the interactionb between upstart and the rolling restart done by sending a USR2 signal to unicorn or rainbows, heretoafter referred to as unicorn.

What you need to know

Unicorn master will be managed correctly by upstart for start, stop and restart. However, in order for your app to correctly handle the reload it needs the following in the unicorn.rb config file.


  • After restart the new unicorn master must load all of the rails code. This can take a while and any code changes will not be visible until it is done loading and has replaced the old master process.

This needs to be anywhere in the top scope of your config file.

# Unicorn will respawn on signal USR2 with this command. By defaults its the same one it was
# launched with. In capistrano style deploys this will always be the same revision
# unless we explicitly point it to the 'current' symlink.
Unicorn::HttpServer::START_CTX[0] = ::File.join(ENV['GEM_HOME'].gsub(/releases\/[^\/]+/, "current"),'bin','unicorn')

This needs to be the contents of your before_exec block. You can have additional config in before_exec but be careful not to disrupt the logic here.

before_exec do |server|
  # Read environment settings from .env. This allows the environment to be changed during a unicorn
  # upgrade via USR2. Remove leading "export " if its there
  env_file = File.join(app_dir, '.env')

  if File.exists?(env_file)
    File.foreach(env_file) do |line|
      name,value = line.split('=').map{ |v| v.strip }
      name.gsub!(/^export /,'')

  # In capistrano style deployments, the newly started unicorn master in no-downtime
  # restarts will get the GEM_HOME from the previous one.
  # By pointing it at the 'current' symlink we know we're up to date.
  # No effect in other types of deployments
  ENV['GEM_HOME'] = ENV['GEM_HOME'].gsub(/releases\/[^\/]+/, "current")

  # put the updated GEM_HOME bin in the path instead of the specific release directory
  # in capistrano like deployments
  paths = (ENV["PATH"] || "").split(File::PATH_SEPARATOR)
  paths.unshift ::File.join(ENV['GEM_HOME'], 'bin')
  ENV["PATH"] = paths.uniq.join(File::PATH_SEPARATOR)

All of this is to tell unicorn to use the new location of the current symlink created by a new slug install instead of the old target directory it was originally pointing to. It also will reread the .env file in the slug's top level directory upon restart.

The details

If your Procfile has a line for either unicorn or rainbows it, upon installation the slug will export an upstart service config file that doesn't start unicorn but starts a shell script called unicorn-shepherd.sh which is packaged in the slug. This script stays alive and gives upstart a constant pid to monitor. The script starts unicorn and waits for the unicorn master pid to die. If it receives a restart command from upstart it will send a USR2 signal to the unicorn master and exit. While unicorn forks a new master and starts rolling new workers, upstart will restart the unicorn-shepherd.sh script which will find the new master and wait for it.


This software is released under the MIT license. See the LICENSE file in the repository for additional details.


Tapjoy is not currently accepting contributions to this code at this time. We are in the process of formalizing our Contributor License Agreement and will update this section with those details when they are available.

Thank You

Thank you to the entire engineering team at Tapjoy. Including, but not limited to, @jjrussell, @andyleclair, @jlogsdon, @ofanite, and @ehealy.