Create VPC and Subnets in Availability Zones

This module's default behaviour is to create a VPC and then create one private and one public subnet per availability zone in the VPC's region. In Frankfurt 6 subnets would be created as there are 3 availability zones.

Module Usage

module vpc-network
{
    source  = "devops4me/vpc-network/aws"
    version = "~> 1.0.3"

    in_vpc_cidr            = "10.245.0.0/16"
    in_num_private_subnets = 6
    in_num_public_subnets  = 3
}

The most common use case is to specify the VPC Cidr, the number of public and private subnets.

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Run the Example

You can run the example to see this module create a number of VPCs with varying attributes such as the number of private/public subnets.

Module Inputs

Input Variable	Type	Description	Default
in_vpc_cidr	string	The VPC's Cidr defining the range of available IP addresses	10.42.0.0/16
in_num_private_subnets	number	Number of private subnets to create across availability zones	3
in_num_public_subnets	number	Number of public subnets to create across availability zones. If one or more an internet gateway and route to the internet will be created regardless of the value of the in_create_gateway boolean variable.	3
in_create_public_gateway	bool	if true create an internet gateway and routes so services can access the internet.	true
in_create_private_gateway	bool	if true creates a NAT gateway and private routes for egress access from private subnets.	true
in_subnets_max	number	2 to the power of this is the max number of carvable subnets So 24 = 16 subnets	4

Optional Resource Tag Inputs

Most organisations have a mandatory set of tags that must be placed on AWS resources for cost and billing reports. Typically they denote owners and specify whether environments are prod or non-prod.

Input Variable	Variable Description	Input Example
in_ecosystem	the ecosystem (environment) name these resources belong to	my-app-test or kubernetes-cluster
in_timestamp	the timestamp in resource names helps you identify which environment instance resources belong to	1911021435 as $(date +%y%m%d%H%M%S)
in_description	a human readable description usually stating who is creating the resource and when and where	"was created by $USER@$HOSTNAME on $(date)."

Try echo $(date +%y%m%d%H%M%S) to check your timestamp and echo "was created by $USER@$HOSTNAME on $(date)." to check your description. Here is how you can send these values to terraform.

$ export TF_VAR_in_timestamp=$(date +%y%m%d%H%M%S)
$ export TF_VAR_in_description="was created by $USER@$HOSTNAME on $(date)."

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subnets into availability zones | round robin

You can create more or less subnets than there are availability zones in the VPC's region. You can ask for 6 private subnets in a 3 availability zone region. The subnets are distributed into the availability zones like dealing a deck of cards.

Every permutation of subnets and availability zones is catered for so you can demand

• less subnets than availability zones (so some won't get any)
• a subnet count that is an exact multiple of the zone count (equality reigns)
• that no subnets (public and/or private) get created
• nothing - and each availability zone will get one public and one private subnet

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internet gateway and route

This module senses whether you wish to create an internet gateway (in) and a route (out) to the internet.

If in_num_public_subnets is greater than zero it automatically creates an internet gateway and a route along with the public subnets. This behaviour can be switched off by setting in_ignore_public to true.

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output variables

Here are the most popular output variables exported from this VPC and subnet creating module.

Exported	Type	Example	Comment
out_vpc_id	String	vpc-1234567890	the VPC id of the just-created VPC
out_rtb_id	String	"rtb-2468013579"	ID of the VPC's default route table
out_subnet_ids	List of Strings	[ "subnet-545123498798345", "subnet-83507325124987" ]	list of all private and public subnet ids
out_private_subnet_ids	List of Strings	[ "subnet-545123498798345", "subnet-83507325124987" ]	list of private subnet ids
out_public_subnet_ids	List of Strings	[ "subnet-945873408204034", "subnet-8940202943031" ]	list of public subnet ids

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Resources Created

This module houses your infrastructure within a secure VPC and it creates the networking resources for routing traffic to your services and conversely enabling your services to access the internet. This module creates

• a VPC (virtual private cloud)
• subnets within the VPC across one or more availability zones
• an internet gateway unless in_num_public_subnets is zero
• an elastic IP address unless in_num_public_subnets is zero
• a nat gateway attached to public subnets for routing outgoing traffic
• route tables along with the necessary public and private routes
• associations that bind subnets to route tables

The subnets are dished out across availability zones in a round robin fashion. You can request less, the same or more (private/public) subnets than there are availability zones.