Provision Infrastructure with Terraform

IaC via Terraform → provision, version, manage cloud resources across AWS, Azure, GCP, other providers.

Use When

• New cloud infra (VPCs, compute, storage, DBs)
• Migrate ClickOps/CloudFormation → declarative IaC
• Multi-env infra (dev, staging, prod)
• Reproducible infra patterns across teams
• Version infra changes w/ app code
• Enforce infra standards via reusable modules

In

• Required: Terraform CLI installed (terraform --version)
• Required: Cloud provider creds (AWS, Azure, GCP service accounts)
• Required: Remote state backend config (S3, Azure Storage, Terraform Cloud)
• Optional: Existing infra to import or migrate
• Optional: Terraform Cloud/Enterprise for team collab
• Optional: Pre-commit hooks for validation + formatting

Do

See Extended Examples for complete config files + templates.

Step 1: Init Terraform Project Structure

Organized dir structure w/ backend config + provider setup.

# Create project structure
mkdir -p terraform/{modules,environments/{dev,staging,prod}}
cd terraform

# Create backend configuration
cat > backend.tf <<'EOF'
terraform {
  required_version = ">= 1.6"

  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }

  backend "s3" {
    bucket         = "my-terraform-state"
    key            = "infrastructure/terraform.tfstate"
    region         = "us-east-1"
    encrypt        = true
    dynamodb_table = "terraform-lock"

    # Workspace-specific state files
    workspace_key_prefix = "env"
  }
}

provider "aws" {
  region = var.aws_region

  default_tags {
    tags = {
      ManagedBy   = "Terraform"
      Environment = terraform.workspace
      Project     = var.project_name
    }
  }
}
EOF

# Create variables file
cat > variables.tf <<'EOF'
variable "aws_region" {
  description = "AWS region for resources"
  type        = string
  default     = "us-east-1"
}

variable "project_name" {
  description = "Project name for resource naming and tagging"
  type        = string
  validation {
    condition     = length(var.project_name) > 0 && length(var.project_name) <= 32
    error_message = "Project name must be 1-32 characters"
  }
}

variable "environment" {
  description = "Environment name (dev, staging, prod)"
  type        = string
  validation {
    condition     = contains(["dev", "staging", "prod"], var.environment)
    error_message = "Environment must be dev, staging, or prod"
  }
}
EOF

# Initialize Terraform
terraform init

→ Terraform inits successfully, downloads provider plugins, configs remote backend. .terraform/ w/ provider binaries. State backend connection verified.

If err: backend init fails → verify S3 bucket exists + IAM perms allow s3:GetObject, s3:PutObject, dynamodb:GetItem, dynamodb:PutItem. Provider download fails → check network + corporate proxy. terraform init -upgrade to update.

Step 2: Create Reusable Infra Modules

Composable modules for VPC, compute, data infra w/ input validation.

# modules/vpc/main.tf
variable "vpc_cidr" {
  description = "CIDR block for VPC"
  type        = string
  default     = "10.0.0.0/16"
}

variable "availability_zones" {
  description = "List of AZs to use"
  type        = list(string)
}

variable "project_name" {
  description = "Project name for resource naming"
  type        = string
}

variable "environment" {
  description = "Environment name"
  type        = string
}

locals {
  common_tags = {
    Project     = var.project_name
    Environment = var.environment
    Module      = "vpc"
  }
}

resource "aws_vpc" "main" {
  cidr_block           = var.vpc_cidr
  enable_dns_hostnames = true
  enable_dns_support   = true

  tags = merge(local.common_tags, {
    Name = "${var.project_name}-${var.environment}-vpc"
  })
}

resource "aws_subnet" "public" {
  count             = length(var.availability_zones)
  vpc_id            = aws_vpc.main.id
  cidr_block        = cidrsubnet(var.vpc_cidr, 8, count.index)
  availability_zone = var.availability_zones[count.index]

  map_public_ip_on_launch = true

  tags = merge(local.common_tags, {
    Name = "${var.project_name}-${var.environment}-public-${var.availability_zones[count.index]}"
    Type = "public"
  })
}

resource "aws_subnet" "private" {
  count             = length(var.availability_zones)
  vpc_id            = aws_vpc.main.id
  cidr_block        = cidrsubnet(var.vpc_cidr, 8, count.index + 100)
  availability_zone = var.availability_zones[count.index]

  tags = merge(local.common_tags, {
    Name = "${var.project_name}-${var.environment}-private-${var.availability_zones[count.index]}"
    Type = "private"
  })
}

resource "aws_internet_gateway" "main" {
  vpc_id = aws_vpc.main.id

  tags = merge(local.common_tags, {
    Name = "${var.project_name}-${var.environment}-igw"
  })
}

resource "aws_eip" "nat" {
  count  = length(var.availability_zones)
  domain = "vpc"

  tags = merge(local.common_tags, {
    Name = "${var.project_name}-${var.environment}-nat-eip-${var.availability_zones[count.index]}"
  })

  depends_on = [aws_internet_gateway.main]
}

resource "aws_nat_gateway" "main" {
  count         = length(var.availability_zones)
  allocation_id = aws_eip.nat[count.index].id
  subnet_id     = aws_subnet.public[count.index].id

  tags = merge(local.common_tags, {
    Name = "${var.project_name}-${var.environment}-nat-${var.availability_zones[count.index]}"
  })

  depends_on = [aws_internet_gateway.main]
}

# modules/vpc/outputs.tf
output "vpc_id" {
  description = "VPC ID"
  value       = aws_vpc.main.id
}

output "public_subnet_ids" {
  description = "List of public subnet IDs"
  value       = aws_subnet.public[*].id
}

output "private_subnet_ids" {
  description = "List of private subnet IDs"
  value       = aws_subnet.private[*].id
}

output "nat_gateway_ips" {
  description = "List of NAT Gateway public IPs"
  value       = aws_eip.nat[*].public_ip
}

→ Module creates VPC w/ public/private subnets across AZs, IGW, NAT GWs w/ EIPs. Outputs expose resource IDs for downstream modules.

If err: CIDR overlap → adjust cidrsubnet() calc or validate VPC CIDR doesn't conflict. Dependency errors → verify depends_on ensures proper creation order. terraform graph | dot -Tpng > graph.png to viz.

Step 3: Implement Env-Specific Configs

Env workspaces w/ var overrides + data sources.

# environments/prod/main.tf
terraform {
  required_version = ">= 1.6"
}

# Import shared backend and provider config
# ... (see EXAMPLES.md for complete configuration)

→ Env-specific config creates prod-sized infra w/ 3 AZs, larger instance types, prod security. Data sources resolve latest AMI. Templates render w/ env vars.

If err: workspace errors → terraform workspace new prod. Data source fails → verify AWS creds have ec2:DescribeImages perms. Template rendering errors → validate var types match template expectations.

Step 4: Execute Plan + Apply Workflow

Run plan, review changes, apply w/ approval.

# Format code
terraform fmt -recursive

# Validate configuration
terraform validate

# ... (see EXAMPLES.md for complete configuration)

CI/CD integration:

# .github/workflows/terraform.yml
name: Terraform

on:
  pull_request:
    paths:
# ... (see EXAMPLES.md for complete configuration)

→ Plan shows resource additions/changes/deletions. No drift detected. Apply creates/updates w/o errors. Outputs contain expected values. CI workflow comments plan on PRs, auto-applies on main merges.

If err: plan fails → terraform validate for syntax. State lock errors → identify holder via aws dynamodb get-item --table-name terraform-lock --key '{"LockID":{"S":"terraform-state-bucket/key"}}', force-unlock if stale. Apply fails → check CloudWatch for provider errors. terraform show to inspect current state.

Step 5: Manage State + Drift Detection

State locking, backup, automated drift detection.

# Create DynamoDB table for state locking
cat > state-backend.tf <<'EOF'
resource "aws_dynamodb_table" "terraform_lock" {
  name           = "terraform-lock"
  billing_mode   = "PAY_PER_REQUEST"
  hash_key       = "LockID"
# ... (see EXAMPLES.md for complete configuration)

Auto drift detection:

# Create drift detection script
cat > scripts/detect-drift.sh <<'EOF'
#!/bin/bash
set -euo pipefail

cd terraform
# ... (see EXAMPLES.md for complete configuration)

→ State backend w/ versioning + encryption. Drift detection IDs out-of-band changes. State ops (list, show, mv, import) w/o errors. Auto drift checks on schedule + alerts.

If err: state lock timeouts → verify DynamoDB table exists w/ correct key schema. Versioning issues → check S3 versioning via aws s3api get-bucket-versioning --bucket bucket-name. Import fails → verify resource exists + Terraform config matches actual attributes.

Step 6: Module Testing + Documentation

Auto tests w/ Terratest + generate docs.

// test/vpc_test.go
package test

import (
    "testing"

# ... (see EXAMPLES.md for complete configuration)

Generate docs:

# Install terraform-docs
go install github.com/terraform-docs/terraform-docs@latest

# Generate module documentation
terraform-docs markdown table modules/vpc > modules/vpc/README.md

# ... (see EXAMPLES.md for complete configuration)

→ Terratest validates module creates expected resources w/ correct config. Docs auto-gen from var descriptions + outputs. Pre-commit hooks enforce formatting + validation.

If err: Terratest fails → check AWS creds + quotas. Long tests → parallel via t.Parallel(). Doc gen errors → verify all vars have description. Pre-commit fails → manually terraform fmt + fix validation.

Check

• Backend w/ encryption, versioning, state locking
• All modules have input validation + outputs
• Workspaces isolate env-specific state
• terraform plan shows no unexpected changes after apply
• Drift detection auto runs + alerts
• Modules tested w/ Terratest or similar
• Docs auto-gen + up-to-date
• Secrets via AWS Secrets Manager, not hardcoded
• Cost estimation integrated (Infracost or similar)
• Blast radius min w/ separate state per env

Traps

• Hardcoded values: Avoid AMI IDs, AZs, account-specific. Use data sources + vars.
• Missing lifecycle blocks: Resources recreate unexpectedly. Add lifecycle { create_before_destroy = true } → prevent downtime during updates.
• No state locking: Concurrent applies corrupt state. Always DynamoDB for locking w/ S3 backend.
• Overly permissive IAM: Terraform service account full admin. Implement least-privilege scoped to managed resources.
• No version constraints: Provider updates break infra. Pin via version = "~> 5.0" constraints.
• Secrets in state: Sensitive values plaintext in state. Use sensitive = true on outputs, store in AWS Secrets Manager, ref via data sources.
• No backup strategy: State file lost/corrupted, no recovery plan. Enable S3 versioning, regular backups, test recovery.
• Monolithic config: Single state file manages everything. Split into logical boundaries (networking, compute, data) → reduce blast radius.

→

• configure-git-repository — version control for Terraform code
• build-ci-cd-pipeline — automated Terraform workflows w/ GitHub Actions
• implement-gitops-workflow — ArgoCD/Flux integration w/ Terraform
• manage-kubernetes-secrets — secrets mgmt in Terraform-provisioned clusters
• deploy-to-kubernetes — Terraform Kubernetes provider usage