Learn how to create reusable Terraform modules. Module structure, versioning, and best practices for infrastructure as code.

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Terraform Modules Best Practices: Building Reusable Infrastructure

Terraform modules enable code reuse. This guide covers module best practices.

Module Structure #

code

modules/
  vpc/
    main.tf
    variables.tf
    outputs.tf
    README.md

Module Definition #

hcl.hcl

# modules/vpc/main.tf
resource "aws_vpc" "main" {
  cidr_block           = var.cidr_block
  enable_dns_hostnames = var.enable_dns_hostnames
  
  tags = merge(
    var.tags,
    {
      Name = var.name
    }
  )
}

Variables #

hcl.hcl

# modules/vpc/variables.tf
variable "cidr_block" {
  description = "CIDR block for VPC"
  type        = string
}

variable "enable_dns_hostnames" {
  description = "Enable DNS hostnames"
  type        = bool
  default     = true
}

variable "tags" {
  description = "Tags to apply"
  type        = map(string)
  default     = {}
}

Using Modules #

hcl.hcl

module "vpc" {
  source = "./modules/vpc"
  
  cidr_block           = "10.0.0.0/16"
  enable_dns_hostnames = true
  
  tags = {
    Environment = "production"
  }
}

Best Practices #

Use semantic versioning
Document modules thoroughly
Use variables for flexibility
Output useful values
Test modules independently

Conclusion #

Create reusable modules with clear structure, documentation, and versioning for maintainable infrastructure code.

For Terraform Modules Best Practices: Building Reusable Infrastructure, define pre-deploy checks, rollout gates, and rollback triggers before release. Track p95 latency, error rate, and cost per request for at least 24 hours after deployment. If the trend regresses from baseline, revert quickly and document the decision in the runbook.

Keep the operating model simple under pressure: one owner per change, one decision channel, and clear stop conditions. Review alert quality regularly to remove noise and ensure on-call engineers can distinguish urgent failures from routine variance.

Repeatability is the goal. Convert successful interventions into standard operating procedures and version them in the repository so future responders can execute the same flow without ambiguity.