terraform.aws-baseline-infra/modules/networking/vpc_subnets

Overview

This module performs the following tasks:

• Create VPC, vpcflow log
• Create subnets in every AZ
• Create IGW, NGW

Subnet addressing

Subnet cidrs are calculated automatically. Due to the design of terraform's cidrsubnets, this module has limitations:

• supports 2, 4, 6, or 8 subnets in total.
• hard-coded to work with 2 AZs, regardless of number of AZs available in the region.

Based on the input variables, it will create subnet cidrs using the following function

Private Subnets per az	Public Subnets per az	Function	Example if a /24 is used on VPC
1	0	cidrsubnets(local.vpc-cidr, 1,1)	2 * /25
1	1	cidrsubnets(local.vpc-cidr, 2,2,2,2)	4 * /26
2	1	cidrsubnets(local.vpc-cidr, 3,3,3,3,3,3)	6 * /27
2	2	cidrsubnets(local.vpc-cidr, 4,4,4,4,4,4,4,4)	8 * /28

simple-divide = local.total-no-subnets >=8 ? cidrsubnets(local.vpc-cidr, 4,4,4,4,4,4,4,4) : local.total-no-subnets >=6 ? cidrsubnets(local.vpc-cidr, 3,3,3,3,3,3) : local.total-no-subnets >=4 ? cidrsubnets(local.vpc-cidr, 2,2,2,2) : local.total-no-subnets >=2 ? cidrsubnets(local.vpc-cidr, 1,1) : null

Inputs:

Name	Description	Type	Default	Required
application	name of application	string	none	yes
environment	capacity of environment (prd/dev/lab)	string	none	yes
customer-name	owner of aws resources	string	none	yes
project	name of project	string	none	yes
default-tags	tags to be added to resources	list	none	yes
number-of-private-subnets-per-az	number of private subnets per az	number	0	yes
number-of-public-subnets-per-az	number of public subnets per az	number	0	yes
create-nat-gateway	whether to deploy NAT gateway for private subnets	bool	true	yes
vpc-cidr	VPC cidr	string	none	yes
enable-flowlog	whether to enable vpc flowlog	bool	true	yes
vpcflowlog-retain-days	number of days to retain vpc cloudwatch log	number	90	yes
aws-region-short	short name of aws region (e.g. apne1)	string	none	yes
aws-region	aws region (e.g. ap-northeast-1)	string	none	yes
vpcflowlog-cwl-loggroup-key-arn	kms key alias arn for log group encryption	string	none	yes

Outputs:

Name	Description	Type
vpc_id	vpc id	string
public_subnets	list of cidr blocks	list
private_subnets	list of cidr blocks	list