Get Terraform to use existing AWS subnets in each AZ when creating an instance in each AWS AZ

Question

I have pre-built subnets in each of my three AWS Availability Zones. I need to build an EC2 instance per AZ but they need to use specific subnets that already exist.

How do I go about writing this in Terraform?

I've got this so far:.

# Configure the AWS Provider
provider "aws" {
  region = "eu-west-1"
}

# Specify 3 availability zones from the region
variable "availability_zones" {
  default = ["eu-west-1a", "eu-west-1b", "eu-west-1c"]
}

data "aws_subnet_ids" "private" {
  vpc_id = "${data.aws_vpc.selected.id}"
  tags {
    Name = "private-elb-1a*"
  }
}


#create ec2 instance
resource "aws_instance" "linux-terraform-test-inst" {
  ami                    = "ami-0b77cxxxxxxx" #Ubuntu x86_64
  instance_type          = "t3.micro"
  subnet_id              = "subnet-xxxxxx"
  security_groups = [aws_security_group.sgn-linux-terraform-test.id]

  tags = {
    Name = "linux-terraform-test-inst"
  }
}


#create security group with allowed port and IP ranges
resource "aws_security_group" "sgn-linux-terraform-test" {
  name        = "sgn-linux-terraform-test"
  description = "sgn-linux-terraform-test"
  vpc_id      = "vpc-052xxxxxxxxxxx"

  ingress {
    description = "SSH"
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["172.16.0.0/12", "10.0.0.0/8"]
  }

  ingress {
    description = "HTTPS"
    from_port   = 443
    to_port     = 443
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  ingress {
    description = "HTTPS Test port"
    from_port   = 7443
    to_port     = 7443
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

  tags = {
    Name = "sgn-linux-terraform-test"
  }
}

Hard coding works, but would like for it to be a bit more dynamic. Each subnet in each AZ has a similar name pattern like 'private-elb-*' that could possibly be used.

AZ "eu-west-1a" has a subnet named "private-elb-1a", "eu-west-1b" has a subnet named "private-elb-1b" and "eu-west-1c" has a subnet named "private-elb-1c".

I have thought of using something like this I picked up on another thread. Just not sure how to construct it to use the specific name of an existing subnet.

{ for s in data.aws_subnet.vpc_live : s.availability_zone => s.id... }