Thanks@apparentlymart, who helped to solve this in Terraform discussion

The Security rule:-

resource "aws_security_group_rule" "ingress_rules" {
  count = length(var.ingress_rules)

  type              = "ingress"
  from_port         = var.ingress_rules[count.index].from_port
  to_port           = var.ingress_rules[count.index].to_port
  protocol          = var.ingress_rules[count.index].protocol
  cidr_blocks       = [var.ingress_rules[count.index].cidr_block]
  description       = var.ingress_rules[count.index].description
  security_group_id = aws_security_group.ec2_security_groups.id
}

And the variable:

variable "sg_ingress_rules" {
    type = list(object({
      from_port   = number
      to_port     = number
      protocol    = string
      cidr_block  = string
      description = string
    }))
    default     = [
        {
          from_port   = 22
          to_port     = 22
          protocol    = "tcp"
          cidr_block  = "1.2.3.4/32"
          description = "test"
        },
        {
          from_port   = 23
          to_port     = 23
          protocol    = "tcp"
          cidr_block  = "1.2.3.4/32"
          description = "test"
        },
    ]
}

If you want this to work literally with indexed fields, make it a list(list(string)) and change the default oyter syntax from braces (used for maps) to brackets (used for lists):

variable "sg_ingress_rules" {
    type        = list(list(string))
    default     = [
        [22, 22, "tcp", "1.2.3.4/32", "test"]
        [23, 23, "tcp", "1.2.3.4/32", "test"]
    ]
}

That is a confusing data structure and will be difficult to work with, so I recommend this instead:

variable "sg_ingress_rules" {
    type        = map(map(any))
    default     = {
        thing1 = {from=22, to=22, proto="tcp", cidr="1.2.3.4/32", desc=test"]
        thing2 = {from=23, to=23, proto="tcp", cidr="1.2.3.4/32", desc="test"}
    }
}

You can use better names than the terrible ones I've chosen and then refer to them in your resource:

resource "aws_security_group_rule" "ingress_rules" {
  for_each          = var.ingress_rules
  type              = "ingress"
  from_port         = each.value.from
  to_port           = each.value.to
  protocol          = each.value.proto
  cidr_blocks       = each.value.cidr
  description       = each.value.desc
  security_group_id = aws_security_group.ec2_security_groups.id
}

You'll get multiple named copies of the aws_security_group_rule which better survives insertions and deletions from the ingress_rules variable and will save you headaches. Otherwise you'll get superfluous destroys and creates of rules and sometimes conflicts due to the indexed resources a count creates.

If you are feeling like having some better guardrails on people setting the ingress_rules value you can use object to require and restrict to a particular set of fields with certain types as follows:

variable "sg_ingress_rules" {
    type        = map(object(
      {
        from = number
        to = number
        proto = string
        cidr = string
        desc = string
      }
    ))
    default     = {
        thing1 = {from=22, to=22, proto="tcp", cidr="1.2.3.4/32", desc=test"]
        thing2 = {from=23, to=23, proto="tcp", cidr="1.2.3.4/32", desc="test"}
    }
}

We can do this in a simple way:-

locals {
  ports_in = [
    443,
    80
  ]
  ports_out = [
    0
  ]
}

resource "aws_security_group" "internet_facing_alb" {
  name        = "internetfacing-loadbalancer-sg"
  description = "Security group attached to internet facing loadbalancer"
  vpc_id      = var.vpc_id

  dynamic "ingress" {
    for_each = toset(local.ports_in)
    content {
      description = "Web Traffic from internet"
      from_port   = ingress.value
      to_port     = ingress.value
      protocol    = "tcp"
      cidr_blocks = ["0.0.0.0/0"]
    }
  }
  dynamic "egress" {
    for_each = toset(local.ports_out)
    content {
      description = "Web Traffic to internet"
      from_port   = egress.value
      to_port     = egress.value
      protocol    = "-1"
      cidr_blocks = ["0.0.0.0/0"]
    }
  }
  tags = {
    Name = "internetfacing-loadbalancer-sg"
  }
}