Cap-EC2

Cap-EC2 is used to generate Capistrano namespaces and tasks from Amazon EC2 instance tags, dynamically building the list of servers to be deployed to.

Notes

Cap-EC2 is only compatible with Capistrano 3.x or later; if you want the Capistrano 2.x version, use Capify-EC2. Note that the configuration file (config/ec2.yml) is not compatible between versions either.

This documentation assumes familiarity with Capistrano 3.x.

A number of features that are in Capify-EC2 are not yet available in Cap-EC2, due to the architectural changes in Capistrano 3.x. The following features are missing (this is not an exhaustive list!):

  • rolling deploy (this should be implemented via SSHKit)
  • ELB registration/de-registration (not widely used)
  • using IAM roles to provide credentials
  • Variables set by EC2 tags
  • Connecting to instances via SSH using a convenience task

Pull requests for these would be welcomed, as would sending feedback via the Issues on this project about features you would like.

Installation

gem install cap-ec2

or add the gem to your project's Gemfile.

You will need to create a YAML configuration file at config/ec2.yml that looks like the following:

access_key_id: "YOUR ACCESS KEY"
secret_access_key: "YOUR SECRET KEY"
regions:
 - 'eu-west-1'

You also need to add the gem to your Capfile:

require "cap-ec2/capistrano"

Configuration

Your config/ec2.yml file must contain at least the information above (access_key_id, secret_access_key, regions). Omitting any of these will raise an exception.

The following are optional settings you can use.

  • project_tag

If this is defined, Cap-EC2 will look for a tag with this name when searching for instances belong to this project. Cap-EC2 will look for a value which matches the :application setting in your deploy.rb. The tag name defaults to "Project".

  • stages_tag

If this is defined, Cap-EC2 will look for a tag with this name to determine which instances belong to a given stage. The tag name defaults to "Stage".

  • roles_tag

If this is defined, Cap-EC2 will look for a tag with this name to determine which instances belong to a given role. The tag name defaults to "Roles".

Usage

Imagine you have four servers on EC2 named and tagged as follows:

'Name' Tag 'Roles' Tag 'Stages' Tag
server-1 web production
server-2 web,app production
server-3 app,db production
server-4 web,db,app staging

Imagine also that we've called our app "testapp", as defined in config/deploy.rb like so:

set :application, "testapp"

Defining the roles in config/deploy/[stage].rb

To define a role, edit config/deploy/[stage].rb and add the following:

ec2_role :web

Let's say we edited config/deploy/production.rb. Adding this configuration to the file would assign the role :web to any instance that has the following properties:

  • has a tag called "Roles" that contains the string "web"
  • has a tag called "Project" that contains the string "testapp"
  • has a tag called "Stage" that contains the current stage we're executing (in this case, "production")

Looking at the above table, we can see we would match server-1 and server-2. (You can have multiple roles in tag separated by commas.)

Now we can define the other roles:

ec2_role :app
ec2_role :db

In the "production" stage, the :app role would apply to server-2 and server-3, and the :db role would apply to server-3.

In the "staging" stage, all roles would apply only to server-4.

Passing options to roles

You can pass options when defining your roles. The options are exactly the same as the options that the Capistrano native role definition takes, since they are passed straight through to Capistrano. For example:

ec2_role :app,
  user: 'user_name',
  ssh_options: {
    user: 'user_name', # overrides user setting above
    keys: %w(/home/user_name/.ssh/id_rsa),
    forward_agent: false,
    auth_methods: %w(publickey password)
    password: 'please use keys'
  }

See the example config files Capistrano builds for you in config/deploy for more details.

Note that at the moment there's no way to pass variables in from EC2 tags - but it would be trivial to add.

Tasks and deployment

You can now define your tasks for these roles in exactly the same way as you would if you weren't using this gem.

Utility tasks

Cap-EC2 adds a few utility tasks to Capistrano for displaying information about the instances that you will be deploying to. Note that unlike Capistrano 2.x, all tasks require a stage.

View instances

This command will show you information all the instances your configuration matches for a given stage.

cap [stage] ec2:status

Example:

$ cap production ec2:status

Num  Name                          ID          Type      DNS              Zone        Roles         Stage
00:  server-1-20131030-1144-0      i-abcdefgh  m1.small  192.168.202.248  us-west-2c  banana,apple  production
01:  server-2-20131118-1839-0      i-hgfedcba  m1.small  192.168.200.60   us-west-2a  banana        production

View server names

This command will show you the server names of the instances matching the given stage:

cap [stage] ec2:server_names

Example:

$ cap production ec2:server_names
server-1-20131030-1144-0
server-2-20131118-1839-0

View server instance IDs

This command will show the instance IDs of the instances matching the given stage:

cap [stage] ec2:instance_ids

Example:

$ cap production ec2:instance_ids
i-abcdefgh
i-hgfedcba

Contributing

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request