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aws_subnet resource

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Use the aws_subnet InSpec audit resource to test properties of a vpc subnet.

Syntax

An aws_subnet resource block uses the parameter to select a VPC and a subnet in the VPC.

describe aws_subnet(subnet_id: 'subnet-1234567') do
  it { should exist }
end

Parameters

subnet_id (required)

This resource accepts a single parameter, the Subnet ID. This can be passed either as a string or as a subnet_id: 'value' key-value entry in a hash.

See also the AWS documentation on Subnets.

Properties

Property Description
subnet_id Provides the ID of the Subnet.
vpc_id Provides the ID of the VPC the subnet is in.
availability_zone Provides the Availability Zone of the subnet.
cidr_block Provides the block of ip addresses specified to the subnet.
available_ip_address_count Provides the number of available IPv4 addresses on the subnet.

Examples

Check availability zone of a subnet

describe aws_subnet(subnet_id: 'subnet-12345678') do
  its('availability_zone') { should eq 'us-east-1c' }
end

Check the number of available IP addresses

describe aws_subnet(subnet_id: 'subnet-12345678') do
  its('available_ip_address_count') { should eq 251 }
end

Test the block of ip addresses specified to the subnet

describe aws_subnet(subnet_id: 'subnet-12345678') do
  its('cidr_block') { should eq '10.0.1.0/24' }
end

Ensure the subnet is in the right VPC

describe aws_subnet(subnet_id: 'subnet-12345678') do
  its('vpc_id') { should eq 'vpc-12345678' }
end

Matchers

This InSpec audit resource has the following special matchers. For a full list of available matchers, please visit our matchers page.

assigning_ipv_6_address_on_creation

Detects if the network interface on the subnet accepts IPv6 addresses.

describe aws_subnet(subnet_id: 'subnet-12345678') do
  it { should be_assigning_ipv_6_address_on_creation }
end

available

Provides the current state of the subnet.

describe aws_subnet(subnet_id: 'subnet-12345678') do
  it { should be_available }
end

default_for_az

Detects if the subnet is the default subnet for the Availability Zone.

describe aws_subnet(subnet_id: 'subnet-12345678') do
  it { should be_default_for_az }
end

mapping_public_ip_on_launch

Provides the VPC ID for the subnet.

describe aws_subnet(subnet_id: 'subnet-12345678') do
  it { should be_mapping_public_ip_on_launch }
end

exist

The exist matcher indicates that a subnet exists for the specified vpc.

describe aws_subnet(subnet_id: 'subnet-12345678') do
  it { should exist }
end

AWS Permissions

Your Principal will need the ec2:DescribeSubnets action with Effect set to Allow.

You can find detailed documentation at Actions, Resources, and Condition Keys for Amazon EC2.

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