Terraform Language Patterns Cheat Sheet

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High-value HCL patterns for variables, locals, outputs, loops, conditionals, dynamic blocks, and data shaping.

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Variables, Locals, Outputs

Common building blocks in Terraform language.

String variable

Declare a typed string variable.

hclANYterraformvariableshcl

↗#

hcl

variable "environment" {
  type        = string
  description = "Deployment environment"
}

Notes

Declare a typed string variable.

Object variable

Declare a typed object variable.

hclANYterraformvariablesobject

↗#

hcl

variable "subnet" {
  type = object({
    cidr = string
    az   = string
  })
}

Notes

Declare a typed object variable.

Locals block

Compute reusable values in locals.

hclANYterraformlocals

↗#

hcl

locals {
  common_tags = {
    app         = "web"
    environment = var.environment
  }
}

Notes

Compute reusable values in locals.

Sensitive output

Mark an output sensitive to reduce accidental display.

hclANYterraformoutputsensitive

↗#

hcl

output "db_password" {
  value     = random_password.db.result
  sensitive = true
}

Notes

Mark an output sensitive to reduce accidental display.

Meta-arguments

Count, for_each, depends_on, lifecycle, and providers.

Use count

Create multiple similar resources with count.

hclANYterraformcountmeta-arguments

↗#

hcl

resource "aws_instance" "web" {
  count = 2
  ami   = var.ami_id
  instance_type = "t3.micro"
}

Notes

Create multiple similar resources with count.

Use for_each

Create resources keyed by map/set members.

hclANYterraformfor_eachmeta-arguments

↗#

hcl

resource "aws_s3_bucket" "logs" {
  for_each = toset(["app","elb","audit"])
  bucket   = "${var.prefix}-${each.key}"
}

Notes

Create resources keyed by map/set members.

Explicit dependency

Force resource ordering when dependency is not inferred from arguments.

hclANYterraformdepends_on

↗#

hcl

resource "aws_instance" "web" {
  # ...
  depends_on = [aws_internet_gateway.this]
}

Notes

Force resource ordering when dependency is not inferred from arguments.

Lifecycle rules

Control replace/delete behavior and ignored drift.

hclANYterraformlifecycle

↗#

hcl

resource "aws_s3_bucket" "logs" {
  bucket = var.bucket_name
  lifecycle {
    prevent_destroy = true
    ignore_changes  = [tags]
  }
}

Notes

Control replace/delete behavior and ignored drift.

Expressions and Functions

Conditional logic, loops, and data transformations.

Conditional expression

Choose values conditionally.

hclANYterraformconditionalexpressions

↗#

hcl

instance_type = var.environment == "prod" ? "t3.large" : "t3.micro"

Notes

Choose values conditionally.

For expression

Transform collections with a for expression.

hclANYterraformfor-expression

↗#

hcl

locals {
  private_subnet_ids = [for s in aws_subnet.private : s.id]
}

Notes

Transform collections with a for expression.

Merge maps

Combine multiple maps into one.

hclANYterraformfunctionsmerge

↗#

hcl

locals {
  tags = merge(local.common_tags, { owner = "platform" })
}

Notes

Combine multiple maps into one.

try and can

Handle optional values and guard against invalid access.

hclANYterraformfunctionstrycan

↗#

hcl

locals {
  instance_arn = try(aws_instance.web.arn, null)
  has_name     = can(var.config.name)
}

Notes

Handle optional values and guard against invalid access.

templatefile function

Render a file template with variables.

hclANYterraformfunctionstemplatefile

↗#

hcl

user_data = templatefile("${path.module}/user-data.sh.tftpl", {
  environment = var.environment
})

Notes

Render a file template with variables.

Dynamic Blocks and Data Sources

Patterns for nested repeated blocks and lookup resources.

Dynamic block

Generate repeated nested blocks from input data.

hclANYterraformdynamic-block

↗#

hcl

dynamic "ingress" {
  for_each = var.ingress_rules
  content {
    from_port   = ingress.value.from_port
    to_port     = ingress.value.to_port
    protocol    = ingress.value.protocol
    cidr_blocks = ingress.value.cidr_blocks
  }
}

Notes

Generate repeated nested blocks from input data.

Data source example

Query existing infrastructure data for use in resources.

hclANYterraformdata-source

↗#

hcl

data "aws_ami" "ubuntu" {
  most_recent = true
  owners      = ["099720109477"]

  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-jammy-22.04-amd64-server-*"]
  }
}