Get Running Instance ID

ec2_helper.rb

require 'aws-sdk'

# Return only a single running instance with the Name tag specified

class EC2Helper
    def self.GetIdFromName(name)
        instances = Array.new
        # Filter the ec2 instances for name and state pending or running
        ec2 = Aws::EC2::Resource.new(region: ENV['AWS_DEFAULT_REGION'])
        ec2.instances({filters: [
            {name: 'tag:Name', values: [name]},
            {name: 'instance-state-name', values: [ 'pending', 'running']}
        ]}).each do |i|
            instances.push(i.id)
        end

        # If we found a single instance return it, otherwise throw an error.
        if instances.count == 1 then
            puts 'Found Running EC2 with Name: ' + name + ' ID: ' + instances[0]
            return instances[0]
        elsif instances.count == 0 then
            STDERR.puts 'Error: ' + name + ' Instance not found'
        else
            STDERR.puts 'Error: ' + name + ' more than one running instance exists with that Name'
        end
    end
end

Following some Ruby idioms:

module EC2Helper
  def self.get_id_from_name(name)
    # Filter the ec2 instances for name and state pending or running
    ec2 = Aws::EC2::Resource.new(region: ENV['AWS_DEFAULT_REGION'])    
    instances = ec2.instances({ filters: [
      { name: "tag:Name", values: [name] },
      { name: "instance-state-name", values: [ "pending", "running"] }
    ]}).map(&:id)

    if instances.count == 1
      instances[0]
    elsif instances.count == 0
      STDERR.puts "Error: '#{name}' Instance not found"
      []
    else
      STDERR.puts "Error: more than one running instance exists with name '#{name}'"
      instances
    end
  end
end