E-Star Technical test

Overview

This repository contains sufficient Terraform code to bring up the networking infrastructure described in the requirements of the technical test.

The resource creation and so on is contained in a module, module/network/, which is called with relevant input values in the accompanying directory, projects/

Subnets are automatically calculated, using the cidrsubnet() function. The important values here are public_subnet_newbits and private_subnet_newbits. In this contexxt "newbits" refers to the size of the subnets in CIDR notation. So, for a VPC with a /16 CIDR block, to create a subnet of /24 would require a newbits value of 8. See here for more details.

The module accepts a list of VPC CIDR blocks, in case multiple VPCs need to be created using the code.

Usage

To use the module, cd to the project/ directory. Set the vpc_cidrs variable - it must be a list of CIDR blocks, even if the list only contains one item. The requirement of this exercise requires:

vpc_cidrs = [
  "10.0.0.0/16"
]

and run:

# terraform init

This will initialise Terraform by downloading the AWS provider and the necessary module.

# terraform plan 

This compares the state file (if any) with information from the AWS API to decide if infrastructure needs creating or destroying.

# terraform apply

This applies the plan and creates or destroys infrastructure as required

Caveats

• The supplied values for vpc_cidrs must be a list of valid IPv4 CIDR blocks and the toset() function must be used to feed in the values using a for_each loop

• The newbits value must be compatible with the VPC's CIDR block. So a VPC with a /24 CIDR block cannot have a newbits value greater than 8 for its subnets.