How to modify "availability_zone" when subnets is greater than availability zones?

Question

I have aws_subnet resource which looks as below:

resource "aws_subnet" "public_subnets" {
  cidr_block              = element(concat(var.psubnets, [""]), count.index)
  availability_zone       = element(var.azs, count.index)
  count                   = length(var.psubnets)
}

Here, how to update availability_zone = element(var.azs, count.index) to account for the situation when

len.subnets > len.azs

Answer 1

The modulus operator should help you account for this:

element(var.azs, count.index % len(var.azs))

For example if the len(var.azs) value is 3, and you had 7 subnets, you would get the following:

count.index	len(var.azs)	count.index % len(var.azs)
0	3	0
1	3	1
2	3	2
3	3	0
4	3	1
5	3	2
6	3	0