Terraform 0.12: HCL2 and Provider Improvements

If you haven’t upgraded to Terraform 0.12 yet, now’s the time. The new HCL2 syntax is a game-changer for infrastructure code. Here’s what changed.

Major Improvements

• First-class expressions: No more interpolation everywhere
• For expressions: Transform collections inline
• Dynamic blocks: Generate nested blocks programmatically
• Improved type system: Better validation and error messages

Old vs New Syntax

# Old (0.11)
resource "azurerm_resource_group" "example" {
  name     = "${var.environment}-rg"
  location = "${var.location}"
}

# New (0.12)
resource "azurerm_resource_group" "example" {
  name     = "${var.environment}-rg"  # Interpolation still works
  location = var.location              # But not required for simple refs
}

For Expressions

# Transform list
tags = { for k, v in var.tags : k => upper(v) }

# Filter list  
enabled_users = [for u in var.users : u.name if u.is_enabled]

Dynamic Blocks

resource "azurerm_network_security_group" "example" {
  name = "example-nsg"
  
  dynamic "security_rule" {
    for_each = var.security_rules
    content {
      name      = security_rule.value.name
      priority  = security_rule.value.priority
      direction = security_rule.value.direction
    }
  }
}

References

• Terraform 0.12 Upgrade Guide