Guides

Terraform Modules: VPC और EC2 Code दोबारा इस्तेमाल करें

By Ravindra Bagale, DevOps trainer · LinkedIn · Published: 28 October 2026 · Last updated: 28 October 2026

VPC/EC2 module folders, variables/outputs, root call, wire, init/validate, version pin.

Language: English · मराठी · हिंदी

Modules क्यों

copy-paste drift रोकें.

Why: दो copies अलग. What: folder modules. How: root अलग vars.

Example 1: Module folder layout

Type this:

mkdir -p /tmp/tfmod/modules/vpc && printf '%s\n' 'variable "cidr" { type = string }' 'output "vpc_id" { value = "vpc-demo" }' > /tmp/tfmod/modules/vpc/main.tf && ls /tmp/tfmod/modules/vpc

You will see:

main.tf

What it means: A module is a folder with variables, resources, outputs.

Example 2: Root calls the module

Type this:

printf '%s\n' 'module "vpc" {' '  source = "./modules/vpc"' '  cidr   = "10.0.0.0/16"' '}' > /tmp/tfmod/main.tf && cat /tmp/tfmod/main.tf

You will see:

module "vpc" {

What it means: source points at the folder; inputs are arguments.

Example 10: Do not copy-paste stacks

Type this:

printf '%s\n' 'ok: one vpc module called from dev and prod with different cidr'

You will see:

ok: one vpc module called from dev and prod with different cidr

What it means: Copy-paste drifts — modules stop that.

Concept 1: Wire

output → input.

Why: hard-code subnet टूटता है. What: vpc → web. How: root outputs.

Example 3: EC2 module sketch

Type this:

mkdir -p /tmp/tfmod/modules/ec2 && printf '%s\n' 'variable "instance_type" { type = string }' 'variable "subnet_id" { type = string }' 'output "instance_id" { value = "i-demo" }' > /tmp/tfmod/modules/ec2/main.tf && cat /tmp/tfmod/modules/ec2/main.tf

You will see:

variable "instance_type" { type = string }

What it means: EC2 module takes subnet from VPC output later.

Example 4: Wire VPC output to EC2

Type this:

printf '%s\n' 'module "web" {' '  source        = "./modules/ec2"' '  instance_type = "t3.micro"' '  subnet_id     = module.vpc.vpc_id' '}' >> /tmp/tfmod/main.tf && tail -6 /tmp/tfmod/main.tf

You will see:

subnet_id     = module.vpc.vpc_id

What it means: Outputs become inputs — Flipkart-style reuse.

Example 9: Output from root

Type this:

printf '%s\n' 'output "web_id" { value = module.web.instance_id }' > /tmp/tfmod/outputs.tf && cat /tmp/tfmod/outputs.tf

You will see:

output "web_id" { value = module.web.instance_id }

What it means: Root outputs expose what CI needs.

Concept 2: Init/plan

module load.

Why: init भूलना. What: init; validate; plan. How: module. prefix.

Example 5: terraform init for modules

Type this:

printf '%s\n' 'terraform init'

You will see:

terraform init

What it means: Downloads/copies module source into .terraform.

Example 6: Plan shows module addresses

Type this:

printf '%s\n' 'terraform plan  # addresses look like module.vpc.aws_vpc.this'

You will see:

terraform plan  # addresses look like module.vpc.aws_vpc.this

What it means: Module prefix keeps state tidy.

Example 11: Validate

Type this:

printf '%s\n' 'terraform validate'

You will see:

terraform validate

What it means: Catches type mistakes before plan.

Concept 3: Pin

version pin.

Why: floating main. What: ref=vX.Y.Z. How: contract.

Example 7: Version pin for remote modules

Type this:

printf '%s\n' 'source = "git::ssh://git.example.internal/tf/vpc.git?ref=v1.2.0"'

You will see:

source = "git::ssh://git.example.internal/tf/vpc.git?ref=v1.2.0"

What it means: Pin ref= — never float on main for prod.

Example 8: Locals for defaults

Type this:

printf '%s\n' 'locals { name_prefix = "pay-dev" }'

You will see:

locals { name_prefix = "pay-dev" }

What it means: Locals keep repeated tags DRY.

Example 12: Module contract

Type this:

printf '%s\n' 'Inputs = variables; outputs = return values; resources stay private inside'

You will see:

Inputs = variables; outputs = return values; resources stay private inside

What it means: Interview one-liner at Cognizant.

Modules card

1 folder 2 vars/outs 3 root 4 wire 5 init 6 pin

Suppose: unknown variable

Declare + pass.

Suppose: bad source

Path/ref.

Check yourself (quiz)

module → call → wire → init → plan. Did you understand? Let us try it once more.