Loops & Conditionals (count, for_each, dynamic)

Let's think about it this way for a second

Instead of manually copy-pasting five resource blocks for five servers, adding `count = 5` inside a resource block makes Terraform create it five times over — you can use `count.index` (0,1,2,3,4) in the resource name/tag. `for_each` is for looping over a list/map — it's better than `count` when you want to track items by a 'meaningful key' (like a server name) instead of an index number (0,1,2): if you delete one item from a list, `count` shifts every index and can recreate every resource, while `for_each` leaves the rest of the items untouched. A dynamic block, meanwhile, is for generating nested blocks (like multiple `ingress` rules in a security group) with a loop.

Let's connect this to a real scenario

Writing `for_each = toset(["web", "api", "worker"])` creates three servers (named web, api, worker) — you can reference `each.key`/`each.value` inside the resource. If you delete 'api' from the server list, `for_each` destroys only 'api' and leaves 'web'/'worker' completely untouched — with `count`, the index shift could recreate every server.

• count = N creates the resource N times over (index-based)
• for_each loops over a list/map (key-based, safer when deleting an item)
• A dynamic block generates nested blocks (like ingress rules) with a loop

Let's look at it together

# count: index-based
resource "aws_instance" "worker" {
  count         = 3
  ami           = "ami-0abcdef1234567890"
  instance_type = "t3.micro"
  tags = {
    Name = "worker-${count.index}"
  }
}

# for_each: key-based (safer when removing items)
resource "aws_instance" "app" {
  for_each      = toset(["web", "api", "worker"])
  ami           = "ami-0abcdef1234567890"
  instance_type = "t3.micro"
  tags = {
    Name = each.value
  }
}

$ terraform apply
aws_instance.app["api"]: Creating...
aws_instance.app["web"]: Creating...
aws_instance.app["worker"]: Creating...

Apply complete! Resources: 3 added, 0 changed, 0 destroyed.