Creating an Amazon EC2 Route Table and Associating It with a Subnet

The following code example creates a route table in Amazon Virtual Private Cloud (Amazon VPC) and then associates the route table with a subnet in Amazon VPC.

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

require 'aws-sdk-ec2'

# Creates a route table in Amazon Virtual Private Cloud (Amazon VPC)
# and then associates the route table with a subnet in Amazon VPC.
#
# Prerequisites:
#
# - A VPC in Amazon VPC.
# - A subnet in that VPC.
# - A gateway attached to that subnet.
#
# @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 route table.
# @param subnet_id [String] The ID of the subnet for the route table.
# @param gateway_id [String] The ID of the gateway for the route.
# @param destination_cidr_block [String] The destination CIDR block
#   for the route. 
# @param tag_key [String] The key portion of the tag for the route table.
# @param tag_value [String] The value portion of the tag for the route table.
# @return [Boolean] true if the route table was created and associated;
#   otherwise, false.
# @example
#   exit 1 unless route_table_created_and_associated?(
#     Aws::EC2::Resource.new(region: 'us-east-1'),
#     'vpc-0b6f769731EXAMPLE',
#     'subnet-03d9303b57EXAMPLE',
#     'igw-06ca90c011EXAMPLE',
#     '0.0.0.0/0',
#     'my-key',
#     'my-value'
#   )
def route_table_created_and_associated?(
  ec2_resource,
  vpc_id,
  subnet_id,
  gateway_id,
  destination_cidr_block,
  tag_key,
  tag_value
)
  route_table = ec2_resource.create_route_table(vpc_id: vpc_id)
  puts "Created route table with ID '#{route_table.id}'."
  route_table.create_tags(
    tags: [
      {
        key: tag_key,
        value: tag_value
      }
    ]
  )
  puts 'Added tags to route table.'
  route_table.create_route(
    destination_cidr_block: destination_cidr_block,
    gateway_id: gateway_id
  )
  puts 'Created route with destination CIDR block ' \
    "'#{destination_cidr_block}' and associated with gateway " \
    "with ID '#{gateway_id}'."
  route_table.associate_with_subnet(subnet_id: subnet_id)
  puts "Associated route table with subnet with ID '#{subnet_id}'."
  return true
rescue StandardError => e
  puts "Error creating or associating route table: #{e.message}"
  puts 'If the route table was created but not associated, you should ' \
    'clean up by deleting the route table.'
  return false
end

# Full example call:
def run_me
  vpc_id = ''
  subnet_id = ''
  gateway_id = ''
  destination_cidr_block = ''
  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-route-table.rb ' \
      'VPC_ID SUBNET_ID GATEWAY_ID DESTINATION_CIDR_BLOCK ' \
      'TAG_KEY TAG_VALUE REGION'
    puts 'Example: ruby ec2-ruby-example-create-route-table.rb ' \
      'vpc-0b6f769731EXAMPLE subnet-03d9303b57EXAMPLE igw-06ca90c011EXAMPLE ' \
      '\'0.0.0.0/0\' 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-0b6f769731EXAMPLE'
    subnet_id = 'subnet-03d9303b57EXAMPLE'
    gateway_id = 'igw-06ca90c011EXAMPLE'
    destination_cidr_block = '0.0.0.0/0'
    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]
    subnet_id = ARGV[1]
    gateway_id = ARGV[2]
    destination_cidr_block = ARGV[3]
    tag_key = ARGV[4]
    tag_value = ARGV[5]
    region = ARGV[6]
  end

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

  if route_table_created_and_associated?(
    ec2_resource,
    vpc_id,
    subnet_id,
    gateway_id,
    destination_cidr_block,
    tag_key,
    tag_value
  )
    puts 'Route table created and associated.'
  else
    puts 'Route table not created or not associated.'
  end
end

run_me if $PROGRAM_NAME == __FILE__