Terraform Syntax (HCL)

Blocks and arguments

Terraform files are made of blocks. A block has a type, zero or more labels, and a body in braces with arguments (name = value) and nested blocks.

resource "aws_instance" "web" {   # block type "resource", labels "aws_instance" and "web"
  ami           = "ami-0abcdef1234567890"
  instance_type = "t3.micro"

  tags = {                        # an argument whose value is a map
    Name = "web-server"
  }
}

Comments

# and // start a single-line comment; /* … */ spans several lines. # is the usual style.

Values

output "examples" {
  value = {
    text    = "a string with ${upper("interpolation")}"
    number  = 42
    decimal = 3.5
    enabled = true
    list    = ["a", "b", "c"]
    map     = { env = "dev", team = "web" }
  }
}

examples = {
  "decimal" = 3.5
  "enabled" = true
  "list" = [
    "a",
    "b",
    "c",
  ]
  "map" = {
    "env" = "dev"
    "team" = "web"
  }
  "number" = 42
  "text" = "a string with INTERPOLATION"
}

Files and order

Terraform reads every .tf file in the directory together, so the order of blocks and files doesn't matter. By convention: main.tf (resources), variables.tf, outputs.tf, providers.tf and versions.tf.

Run terraform fmt to align = signs and indentation automatically.