dennisonbertram/go-code/terraform

# macOS (via Homebrew)
brew tap hashicorp/tap && brew install hashicorp/tap/terraform
 
# Verify installation
terraform version

# 1. Initialize — download providers and modules
terraform init
 
# 2. Format code (auto-fix indentation and style)
terraform fmt -recursive
 
# 3. Validate configuration
terraform validate
 
# 4. Preview changes
terraform plan
 
# 5. Apply changes (with confirmation prompt)
terraform apply
 
# 6. Apply without prompt (for CI/automation)
terraform apply -auto-approve
 
# 7. Destroy all resources
terraform destroy

# Define variables in variables.tf
# variable "region" {
#   type    = string
#   default = "us-east-1"
# }
 
# Override variables on command line
terraform plan -var="region=us-west-2"
 
# Use a variable file (.tfvars)
terraform plan -var-file="prod.tfvars"
 
# Terraform auto-loads terraform.tfvars and *.auto.tfvars
 
# Use environment variables (TF_VAR_ prefix)
export TF_VAR_region="us-west-2"
terraform plan

# main.tf — core resources
terraform {
  required_version = ">= 1.6"
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
  backend "s3" {
    bucket = "my-terraform-state"
    key    = "prod/terraform.tfstate"
    region = "us-east-1"
  }
}
 
provider "aws" {
  region = var.region
}
 
resource "aws_s3_bucket" "app" {
  bucket = "my-app-assets-${var.environment}"
  tags = {
    Environment = var.environment
    ManagedBy   = "terraform"
  }
}
 
output "bucket_name" {
  value = aws_s3_bucket.app.bucket
}

# List all resources in state
terraform state list
 
# Show details of a specific resource
terraform state show aws_s3_bucket.app
 
# Move a resource (rename in state)
terraform state mv aws_s3_bucket.app aws_s3_bucket.assets
 
# Remove a resource from state (does NOT destroy it)
terraform state rm aws_s3_bucket.old
 
# Import an existing resource into state
terraform import aws_s3_bucket.app my-existing-bucket-name
 
# Pull remote state to local (for inspection)
terraform state pull > current.tfstate

# Create S3 bucket for state (one-time setup)
aws s3api create-bucket \
  --bucket my-terraform-state \
  --region us-east-1
 
# Enable versioning (for state history)
aws s3api put-bucket-versioning \
  --bucket my-terraform-state \
  --versioning-configuration Status=Enabled
 
# Enable encryption
aws s3api put-bucket-encryption \
  --bucket my-terraform-state \
  --server-side-encryption-configuration \
    '{"Rules":[{"ApplyServerSideEncryptionByDefault":{"SSEAlgorithm":"AES256"}}]}'

# List workspaces
terraform workspace list
 
# Create and switch to a new workspace
terraform workspace new staging
 
# Switch between workspaces
terraform workspace select production
terraform workspace select staging
 
# Show current workspace
terraform workspace show
 
# Use workspace name in resources
# resource "aws_s3_bucket" "app" {
#   bucket = "myapp-${terraform.workspace}"
# }

# Module usage in main.tf
# module "vpc" {
#   source  = "terraform-aws-modules/vpc/aws"
#   version = "~> 5.0"
#   name    = "my-vpc"
#   cidr    = "10.0.0.0/16"
# }
 
# Download/update module sources
terraform init -upgrade
 
# List all module calls in config
terraform providers

# Save plan to file (for apply in CI)
terraform plan -out=tfplan
terraform apply tfplan
 
# Plan with detailed diff
terraform plan -detailed-exitcode
# Exit 0 = no changes, Exit 1 = error, Exit 2 = changes present
 
# Apply only a specific resource
terraform apply -target=aws_s3_bucket.app
 
# Destroy only a specific resource
terraform destroy -target=aws_s3_bucket.old
 
# Refresh state from real infrastructure
terraform refresh

# Show all outputs after apply
terraform output
 
# Show a specific output value
terraform output bucket_name
 
# Output as JSON
terraform output -json

# Enable verbose logging
TF_LOG=DEBUG terraform plan 2>&1 | head -100
 
# Log to file
TF_LOG=INFO TF_LOG_PATH=./terraform.log terraform apply
 
# Show the dependency graph (requires graphviz)
terraform graph | dot -Tsvg > graph.svg

# Typical CI pipeline steps
terraform init -input=false
terraform validate
terraform fmt -check -recursive        # fail if not formatted
terraform plan -out=tfplan -input=false
terraform apply -input=false tfplan