Format Lifecycle and Meta-Argument Blocks

Formatting Lifecycle Blocks

Lifecycle meta-arguments control how Terraform creates, updates, and destroys resources. They are placed inside the resource block and require careful formatting because they affect critical infrastructure behavior.

Lifecycle Block Examples

resource "aws_instance" "critical" {
  ami           = var.ami_id
  instance_type = var.instance_type

  lifecycle {
    prevent_destroy = true
  }

  tags = {
    Name = "critical-server"
  }
}

resource "aws_launch_template" "web" {
  name_prefix   = "web-"
  image_id      = data.aws_ami.ubuntu.id
  instance_type = var.instance_type

  lifecycle {
    create_before_destroy = true
    ignore_changes = [
      image_id,
      tags,
    ]
  }

  tags = {
    Name = "web-launch-template"
  }
}

resource "aws_ecs_service" "app" {
  name            = "app-service"
  cluster         = aws_ecs_cluster.main.id
  task_definition = aws_ecs_task_definition.app.arn
  desired_count   = var.app_count

  lifecycle {
    ignore_changes = [desired_count]

    replace_triggered_by = [
      aws_ecs_task_definition.app,
    ]
  }
}

Formatting Details

• Single-line vs multi-line: Single-value lifecycle rules (prevent_destroy = true) stay on one line
• List attributes: ignore_changes with multiple values uses a multi-line list with trailing commas
• Single-item lists: ignore_changes = [desired_count] can stay on one line if there is only one item
• Block placement: The lifecycle block is typically placed after resource attributes but before tags
• Separation: A blank line before lifecycle visually separates it from regular attributes

Meta-Argument Ordering Convention

A common ordering convention that the formatter maintains:

1. count or for_each (first)
2. Regular attributes
3. Nested blocks (connection, provisioner)
4. lifecycle block
5. depends_on
6. tags (last)