Attach EBS volumes to EC2 instances for each terraform

Question

I have instances created in a private subnet using terraform. Each instance in its own AZ. The instances were created using for each. I am now attaching ebs volumes to each of the instances and am running into an error specifying the instances created with for each. Below is the code and variables for the resources and the error.

   resource "aws_instance" "private" {
      for_each      = var.priv_subnet
      ami           = var.ec2_amis[var.region]
      instance_type = each.value.instance_type
      key_name      = aws_key_pair.main.key_name
      subnet_id     = aws_subnet.private[each.key].id
      vpc_security_group_ids = [
        aws_security_group.main_sg.id,
        aws_security_group.instance_sg.id
      ]
    
      tags = {
        Name = each.value.tag
      }
    }
    
    resource "aws_ebs_volume" "partition" {
      for_each          = var.volumes
      availability_zone = each.value.availability_zone
      size              = each.value.size
    
      tags = {
        Name = each.key
      }
    }

resource "aws_volume_attachment" "ebs_att" {
  for_each    = aws_ebs_volume.partition
  device_name = contains(["Primary", "Worker1", "Worker2"], each.key) ? "/dev/sdf" : "/dev/sdg"
  volume_id   = each.value.id
  instance_id = aws_instance.private.id
}

Variables

variable "volumes" {
  type = map(object({
    size              = string
    availability_zone = string
  }))
  default = {
    "Primary" = {
      size              = "200"
      availability_zone = "us-west-2a"
    }
    "PrimarySecondary" = {
      size              = "100"
      availability_zone = "us-west-2a"
    }
    "Worker1" = {
      size              = "200"
      availability_zone = "us-west-2b"
    }
    "Worker1Secondary" = {
      size              = "100"
      availability_zone = "us-west-2b"
    }
    "Worker2" = {
      size              = "200"
      availability_zone = "us-west-2c"
    }
    "Worker2Secondary" = {
      size              = "100"
      availability_zone = "us-west-2c"
    }
  }
}

variable "priv_subnet" {
  type = map(object({
    instance_type = string
    subnet        = string
    tag           = string
  }))
  default = {
    "us-west-2a" = {
      instance_type = "m4.2xlarge"
      subnet        = 4
      tag           = "Primary"
    }
    "us-west-2b" = {
      instance_type = "m4.4xlarge"
      subnet        = 5
      tag           = "Worker1"
    }
    "us-west-2c" = {
      instance_type = "m4.4xlarge"
      subnet        = 6
      tag           = "Worker2"
    }
  }
}

Error

Error: Unsupported attribute

 on vpc.tf line 51, in resource "aws_volume_attachment" "ebs_att":
 51:   instance_id = aws_instance.private[each.value.tag].id
   |----------------
   | each.value is object with 12 attributes

This object does not have an attribute named "tag".

Answer 1

I had to specify:

instance_id = aws_instance.private[each.value.availability_zone].id

in aws_volume_attachment resource