Terraform Classroom Series – 21/Sep/2019

Reusability in Terraform using Modules

• Module: Reusable Terraform script/template is called as module
• Things to know:
  • Module is nothing but organizing the same terraform script in a bit different
  • We have sample architecture terraform script. Now i want to convert that to module
  • Like all the components of Terraform. Module also has arguments & attributes
  • varaibles become arguments
  • outputs become attributes
  • In the calling script you will import module
  • There are many modules which you can use. These modules are available in Terraform Registry Refer.

Lets use aws-vpc module from terraform registry

• Refer for documentation
• module syntax in terraform

module "<module name>" {
    source = "<module location>"
    arg1  = value1
    ..
    ..
    ..
    argn = valuen
}

Refer the below sample usage of module

variable "accesskey" {
    type = "string"
}

# required variable secretkey
variable "secretkey" {
    type = "string"
}

# optional region
variable "region" {
    type = "string"
    default = "eu-west-3"
}


provider "aws" {
   region       = "${var.region}"
   access_key   = "${var.accesskey}"
   secret_key   = "${var.secretkey}"
}


module "vpc" {
  source = "terraform-aws-modules/vpc/aws"
  name = "my-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["eu-west-3a", "eu-west-3b", "eu-west-3c"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24", "10.0.3.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24", "10.0.103.0/24"]

  tags = {
    Terraform = "true"
    Environment = "dev"
    Name = "module demo"
  }
  
}

output "vpcid" {
  value = "${module.vpc.vpc_id}"
}

How to Create Module

1. Lets refactor simple architecture.

2. Ensure all the variables are written in a file called as variables.tf (Recomendation)

3. Ensuare all the outputs are written in a file called as outputs.tf (Recomended)

4. whenever you are using local modules try to use the following directory structure ==> Terraform Script => Modules <Modulename> main.tf variables.tf outputs.tf

5. Refer here for the whole template usage

Multi User Scenarios

As mentioned in the above images we need to solve this problem.

Why this problem

• Whenever terraform apply command is executed, a state file gets created.
• Default location of state file is current directory

Possible Solution

• Try to store state file in common location which is accessible to both
• This is called as backend Refer

What about backend with multiple Environments

• Solution to this is Terraform Workspace

Azure Provider

• Manual Reference