sparkle-pack-aws-availability-zones

SparklePack to auto-detect Availability Zones for current Region and return them as an array. h/t to techshell for this approach.

This SparklePack adds a registry entry that uses the AWS SDK to detect the Availability Zones for your region (based on ENV['AWS_REGION']) and returns them as an array. It is useful for any multi-AZ implementation, but especially valuable for creating a codebase that works in any AWS region.

Add the pack to your Gemfile and .sfn:

Gemfile:

source 'https://rubygems.org'

gem 'sfn'
gem 'sparkle-pack-aws-availability-zones'

.sfn:

Configuration.new do
  sparkle_pack [ 'sparkle-pack-aws-availability-zones' ]
  ...
end

In a SparkleFormation Template/Component/Dynamic:

zones = registry!(:zones)

zones will be an array of Availability Zones, e.g. [ 'us-west-2a', 'us-west-2b', 'us-west-2d' ]

This is useful for consistently creating subnets:

zones.each do |zone|
  resource("public_#{zone.gsub('-', '_')}_subnet".to_sym) do
    type 'AWS::EC2::Subnet'
    properties do
      availability_zone zone
      cidr_block ref!("public_#{zone.gsub('-', '_')}_cidr".to_sym)
      vpc_id ref!(vpc_id)
    end
  end
end

You can, of course, work with a subset of the Availability Zones as well:

Return a single AZ:

zone = registry!(:zones).first
zone = registry!(:zones)[2]
zone = registry!(:zones).sample

When returning an index, remember that AWS regions offer varying numbers of Availability Zones.

Set a maximum number of Availability Zones:

zones = registry!(:zones).take(3)