Terraform coerces the literal booleans false and true (e.g., when used as variable values) to 0 and 1 respectively. As a result, this ternary expression:
count = "${var.myboolean == true ? 1 : 0}"unexpectedly always evaluates to 0. You want to use
count = "${var.myboolean ? 1 : 0}"Or even just
count = "${var.myboolean}"if that meets your readability standards.
Being loose with type coercion has its drawbacks...