问Terraform :如何在提供之后将实例IP发送到aws_instances

EN

resource "aws_instance" "A" {
 #provisioning declarations
}

resource "aws_instance" "B" {
  #provisioning declarations
}

# Crux of problem : This should run after all instances are provisioned sending all IPs to each
resource "null_resource" "send_instance_ips" {
  
  depends_on = [aws_instance.A, aws_instance.B] 
  
  for_each = { for idx, instance in [aws_instance.A, aws_instance.B]: idx=> instance}
  
  connection {
    type = "ssh"
    user = "admin-user"
    private_key = file("~/id_rsa")
    host = each.value.public_ip
  }
  
  provisioner "remote-exec" { 
     inline = [
      "echo ${aws_instance.A.*.private_ip} > a_ip.txt",
      "echo ${aws_instance.B.*.private_ip} > b_ip.txt"
    ]
  }     
}

Error: 2 problems:

- Invalid template interpolation value: Cannot include the given value in a string template: string required.
- Invalid template interpolation value: Cannot include the given value in a string template: string required.