Creating a Public Subnet for Amazon EC2

The following code example creates a subnet within a virtual private cloud (VPC) in Amazon Virtual Private Cloud (Amazon VPC) and then tags the subnet.

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

require 'aws-sdk-ec2'

# Creates a subnet within a virtual private cloud (VPC) in 
# Amazon Virtual Private Cloud (Amazon VPC) and then tags
# the subnet.
#
# Prerequisites:
#
# - A VPC in Amazon VPC.
#
# @param ec2_resource [Aws::EC2::Resource] An initialized
#   Amazon Elastic Compute Cloud (Amazon EC2) resource object.
# @param vpc_id [String] The ID of the VPC for the subnet.
# @param cidr_block [String] The IPv4 CIDR block for the subnet.
# @param availability_zone [String] The ID of the Availability Zone
#   for the subnet.
# @param tag_key [String] The key portion of the tag for the subnet. 
# @param tag_vlue [String] The value portion of the tag for the subnet.
# @return [Boolean] true if the subnet was created and tagged;
#   otherwise, false.
# @example
#   exit 1 unless subnet_created_and_tagged?(
#     Aws::EC2::Resource.new(region: 'us-east-1'),
#     'vpc-6713dfEX',
#     '10.0.0.0/24',
#     'us-east-1a',
#     'my-key',
#     'my-value'
#   )
def subnet_created_and_tagged?(
  ec2_resource,
  vpc_id,
  cidr_block,
  availability_zone,
  tag_key,
  tag_value
)
  subnet = ec2_resource.create_subnet(
    vpc_id: vpc_id,
    cidr_block: cidr_block,
    availability_zone: availability_zone
  )
  subnet.create_tags(
    tags: [
      {
        key: tag_key,
        value: tag_value
      }
    ]
  )
  puts "Subnet created with ID '#{subnet.id}' in VPC with ID '#{vpc_id}' " \
    "and CIDR block '#{cidr_block}' in availability zone " \
    "'#{availability_zone}' and tagged with key '#{tag_key}' and " \
    "value '#{tag_value}'."
  return true
rescue StandardError => e
  puts "Error creating or tagging subnet: #{e.message}"
  return false
end

# Full example call:
def run_me
  vpc_id = ''
  cidr_block = ''
  availability_zone = ''
  tag_key = ''
  tag_value = ''
  region = ''
  # Print usage information and then stop.
  if ARGV[0] == '--help' || ARGV[0] == '-h'
    puts 'Usage:   ruby ec2-ruby-example-create-subnet.rb ' \
      'VPC_ID CIDR_BLOCK AVAILABILITY_ZONE TAG_KEY TAG_VALUE REGION'
    puts 'Example: ruby ec2-ruby-example-create-subnet.rb ' \
      'vpc-6713dfEX 10.0.0.0/24 us-east-1a 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?
    vpc_id = 'vpc-6713dfEX'
    cidr_block = '10.0.0.0/24'
    availability_zone = 'us-east-1a'
    tag_key = 'my-key'
    tag_value = 'my-value'
    region = 'us-east-1'
  # Otherwise, use the values as specified at the command prompt.
  else
    vpc_id = ARGV[0]
    cidr_block = ARGV[1]
    availability_zone = ARGV[2]
    tag_key = ARGV[3]
    tag_value = ARGV[4]
    region = ARGV[5]
  end

  ec2_resource = Aws::EC2::Resource.new(region: region)

  if subnet_created_and_tagged?(
    ec2_resource,
    vpc_id,
    cidr_block,
    availability_zone,
    tag_key,
    tag_value
  )
    puts 'Subnet created and tagged.'
  else
    puts 'Subnet not created or not tagged.'
  end
end

run_me if $PROGRAM_NAME == __FILE__