Getting Information about All Amazon EC2 Instances with a Specific Tag Value

The following code example lists the IDs and current states of available Amazon EC2 instances matching the specified tag key and value.

# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
# SPDX - License - Identifier: Apache - 2.0

require 'aws-sdk-ec2'

# Lists the IDs, current states, and tag keys/values of matching
# available Amazon Elastic Compute Cloud (Amazon EC2) instances.
#
# @param ec2_resource [Aws::EC2::Resource] An initialized EC2 resource object.
# @param tag_key [String] The key portion of the tag to search on.
# @param tag_value [String] The value portion of the tag to search on.
# @example
#   list_instance_ids_states_by_tag(
#     Aws::EC2::Resource.new(region: 'us-east-1'),
#     'my-key',
#     'my-value'
#   )
def list_instance_ids_states_by_tag(ec2_resource, tag_key, tag_value)
  response = ec2_resource.instances(
    filters: [
      {
        name: "tag:#{tag_key}",
        values: [tag_value]
      }
    ]
  )
  if response.count.zero?
    puts 'No matching instances found.'
  else
    puts 'Matching instances -- ID, state, tag key/value:'
    response.each do |instance|
      print "#{instance.id}, #{instance.state.name}"
      instance.tags.each do |tag|
        print ", #{tag.key}/#{tag.value}"
      end
      print "\n"
    end
  end
rescue StandardError => e
  puts "Error getting information about instances: #{e.message}"
end

#Full example call:
def run_me
  tag_key = ''
  tag_value = ''
  region = ''
  # Print usage information and then stop.
  if ARGV[0] == '--help' || ARGV[0] == '-h'
    puts 'Usage:   ruby ec2-ruby-example-get-instance-info-by-tag.rb ' \
      'TAG_KEY TAG_VALUE REGION'
    puts 'Example: ruby ec2-ruby-example-get-instance-info-by-tag.rb ' \
      'my-key my-value us-east-1'
    exit 1
  # If no values are specified at the command prompt, use these default values.
  elsif ARGV.count.zero?
    tag_key = 'my-key'
    tag_value = 'my-value'
    region = 'us-east-1'
  # Otherwise, use the values as specified at the command prompt.
  else
    tag_key = ARGV[0]
    tag_value = ARGV[1]
    region = ARGV[2]
  end
  ec2_resource = Aws::EC2::Resource.new(region: region)
  list_instance_ids_states_by_tag(ec2_resource, tag_key, tag_value)
end

run_me if $PROGRAM_NAME == __FILE__