When using Terraform AWS provider aws_launch_template resource I want all EC2 Instances to be launched in the single Availability zone.

resource "aws_instance" "name" {
  count = 11

  launch_template {
    name = aws_launch_template.template_name.name
  }
}

And in the resource aws_launch_template{} in the placement{} block I have defined certain Availability zone:

resource "aws_launch_template" "name" {
  placement {
    availability_zone = "eu-west-3a"
  }
}

But this did not work and all Instances were created in the eu-west-3c Availability Zone.

Does anyone know why that did not work ? And what is the purpose of argument availability_zone in the placement{} block ?