Terraform multiple aws instances multiple subnets

amazon-web-servicesterraform

terraform -v
Terraform v0.12.23
+ provider.aws v2.53.0

I am trying to create 4 instances on put them on 2 different subnets

resource "aws_subnet" "private-subnet-1" {
  vpc_id            = aws_vpc.vpc.id
  cidr_block        = "10.150.2.0/24"
  availability_zone = "us-west-2a"
  tags = {
   Name = "private-subnet-1"
  }
}

resource "aws_subnet" "private-subnet-2" {
  vpc_id            = aws_vpc.vpc.id
  cidr_block        = "10.150.4.0/24"
  availability_zone = "us-west-2b"
  tags = {
   Name = "private-subnet-2"
  }
}

variable "subnet_ids" {
  type    = list(string)
  default = ["aws_subnet.private-subnet-1.id","aws_subnet.private-subnet-2.id"]
}

resource "aws_instance" "web" {
  count = 4
  ami           = "ami-0dc33a373d61e6ce0"
  instance_type = "t2.micro"
  key_name   = "AF_KEY_PAIR"
  subnet_id     = element(var.subnet_ids, count.index)
  vpc_security_group_ids = ["${aws_security_group.web-SG.id}"]
}

When I try to apply I get the follow error

Error: Error launching source instance: InvalidSubnetID.NotFound: The subnet ID 'aws_subnet.private-subnet-1.id' does not exist
        status code: 400, request id: 17b46634-5319-4f78-9898-09142e9cb449
  on test.tf line 175, in resource "aws_instance" "web":
 175: resource "aws_instance" "web" {

Error: Error launching source instance: InvalidSubnetID.NotFound: The subnet ID 'aws_subnet.private-subnet-2.id' does not exist
        status code: 400, request id: d092e6a6-d430-4a28-bd75-5af373c76ac7
  on test.tf line 175, in resource "aws_instance" "web":
 175: resource "aws_instance" "web" {

Error: Error launching source instance: InvalidSubnetID.NotFound: The subnet ID 'aws_subnet.private-subnet-1.id' does not exist
        status code: 400, request id: ec672172-3bf7-4cbb-bce0-ae752c59393f
  on test.tf line 175, in resource "aws_instance" "web":
 175: resource "aws_instance" "web" {

Error: Error launching source instance: InvalidSubnetID.NotFound: The subnet ID 'aws_subnet.private-subnet-2.id' does not exist
        status code: 400, request id: 4136f03c-1a5b-44ab-b0bf-a209134c08c9
  on test.tf line 175, in resource "aws_instance" "web":
 175: resource "aws_instance" "web" {

I have tried to change up the

subnet_id     = element(var.subnet_ids, count.index)

and

variable "subnet_ids" {
  type    = list(string)
  default = [aws_subnet.AF-private-subnet-1.id,aws_subnet.AF-private-subnet-2.id]
}

I still get the same error

When I create the subnet_id manually it will work

subnet_id     = aws_subnet.public-subnet-1.id

Best Answer

The issue you're encountering is how variable subnet_ids is interpreting your list. It's not seeing the ids as variables but instead it's interpreting them as strings.

I used the locals for the variable and it worked as you'd expect.

Try these changes to your code:

locals {
  subs = concat([aws_subnet.private-subnet-1.id], [aws_subnet.private-subnet-2.id])
}

resource "aws_instance" "web" {
  count = 4
  ami           = "ami-0dc33a373d61e6ce0"
  instance_type = "t2.micro"
  key_name   = "AF_KEY_PAIR"
  subnet_id     = element(local.subs, count.index)
  vpc_security_group_ids = ["${aws_security_group.web-SG.id}"]
}

References

Local Values
Expressions

Related Solutions

How to tag and name the EC2 Instance that was launched by an EC2 Spot Request

Spot instances requests are a type of EC2 resource. The AWS documentation notes that this type of resource can be tagged, but the resulting tags are not carried over to the actual instances:

The tags that you create for your Spot Instance requests only apply to the requests. These tags are not added automatically to the Spot Instance that the Spot service launches to fulfill the request. You must add tags to a Spot Instance yourself when you create the Spot Instance request or after the Spot Instance is launched.

So you'll need to add the tags after the instances have launched. You have some options here:

User Data Script on the created instance: Write a user data script that uses command line tools and the EC2 meta data service to allow the instance to discover its instance Id and create tags for itself. You can use the AWS CLI create-tags to tag any of your EC2 resources. Alternatively, you could bake this into the AMI as a startup script for whatever OS you intend to use. In either situation, the instance will have to have sufficient permissions to create EC2 tags for itself.
External Utility that monitors your spot request: You can use one of the AWS SDKs to monitor your spot request and tag the instances once they have been created. AWS has a tutorial on this very topic under the "How to Tag Your Spot Requests and Instances" header. Without getting too verbose, this simply involves polling Describe Spot Instance Requests until a created Instance Id is available, and then calling Create Tags.

Why is the AWS instance’s private IP outside of the subnet’s range

The aws_instance resource in the example does not have the subnet_id attribute provided, so the instance would launch into your account's default subnet for the target region. It's likely that the default subnet is not the one you were trying to use, and so it has a different IP address range.

To fix this, determine the appropriate subnet id and add a subnet_id attribute to your declaration, and then also switch from the security_groups attribute to the vpc_security_group_ids attribute:

resource "aws_instance" "mgmt-jump" {
  count = "${var.mgmt_jump_count}"

  ami           = "${lookup(var.amis, var.region)}"
  instance_type = "t2.micro"

  key_name      = "${var.key_pair}"
  subnet_id     = "subnet-xxxxxxx"

  vpc_security_group_ids = ["${aws_security_group.mgmt-jump-sg.id}"]

  private_ip = "${lookup(var.mgmt_jump_private_ips,count.index)}"

  tags {
    Name        = "mgmt-jump-${count.index+1}"
    category    = "dec"
    environment = "management"
    role        = "jump"
  }
}

Best Answer

Related Solutions

How to tag and name the EC2 Instance that was launched by an EC2 Spot Request

Why is the AWS instance’s private IP outside of the subnet’s range

Related Topic