How to create aws_instance with existing VPC? - amazon-web-services

Question

Is it possible to create an EC2 instance while reusing already existing VPC?
Running the following code yields Error launching source instance: VPCIdNotSpecified: No default VPC for this user. GroupName is only supported for EC2-Classic and default VPC. (status code: 400):
data "aws_security_groups" "my_tib_sg" {
tags = {
Name = "my-security-group"
}
}
resource "aws_instance" "nginx" {
ami = data.aws_ami.aws-linux.id
instance_type = "t2.micro"
key_name = var.key_name
vpc_security_group_ids = [data.aws_security_groups.my_tib_sg.id]
# more, irrelevant stuff...
}
FWIU from the error, the aws_instance block requires a reference to my VPC, which basically exists in my security group. Besides, I can't find a way to refer a VPC in an aws_instance block.
Updating code per answers:
I updated the code per answers below:
data "aws_security_groups" "my_tib_sg" {
tags = {
Name = "my-tib-sg"
}
}
data "aws_subnet" "my_subnet" {
tags = {
Name = "my-tib-subnet-1"
}
}
resource "aws_network_interface" "my_ani" {
subnet_id = data.aws_subnet.my_subnet.id
private_ips = ["10.0.0.10"]
tags = {
Name = "my-tib-ani"
by = "TF_TF"
}
}
resource "aws_instance" "nginx" {
ami = data.aws_ami.aws-linux.id
instance_type = "t2.micro"
key_name = var.key_name
vpc_security_group_ids = [data.aws_security_groups.my_tib_sg.id]
network_interface {
network_interface_id = aws_network_interface.my_ani.id
device_index = 0
}
connection {
type = "ssh"
host = self.public_ip
user = "ec2-user"
private_key = file(var.private_key_path)
}
provisioner "remote-exec" {
inline = [
"sudo yum install nginx -y",
"sudo service nginx start"
]
}
}
But the error changes to "network_interface": conflicts with vpc_security_group_ids.
(needless to mention: both my_subnet and my_tib_sg use same VPC)

Answer 1

I typically use the subnet_id parameter, directly on the aws_instance resource:
data "aws_security_groups" "my_tib_sg" {
tags = {
Name = "my-tib-sg"
}
}
data "aws_subnet" "my_subnet" {
tags = {
Name = "my-tib-subnet-1"
}
}
resource "aws_instance" "nginx" {
ami = data.aws_ami.aws-linux.id
instance_type = "t2.micro"
key_name = var.key_name
vpc_security_group_ids = [data.aws_security_groups.my_tib_sg.ids[0]]
# specify the subnet_id here
subnet_id = data.aws_subnet.my_subnet.id
# more, irrelevant stuff...
}

Answer 2

Yes, you can add a new EC2 instance to an existing VPC.
You should provide the subnet_id to aws_instance. You would typically pass that into Terraform as a parameter, rather than hard-coding its value into your template.
Note: the subnet ID implicitly indicates the actual VPC (because a subnet only exists in one VPC).

Answer 3

Is it possible to create an EC2 instance while reusing already existing VPC?
yes you can create an ec2 instance with an existing VPC. You can use a Data Source: aws_vpc to query existing VPC and then further reference the same in your resource like Resource: aws_instance below:
variable "vpc_id" {}
data "aws_vpc" "selected" {
id = var.vpc_id
}
resource "aws_subnet" "example" {
vpc_id = data.aws_vpc.selected.id
availability_zone = "us-west-2a"
cidr_block = cidrsubnet(data.aws_vpc.selected.cidr_block, 4, 1)
}
resource "aws_security_group" "allow_tls" {
name = "allow_tls"
description = "Allow TLS inbound traffic"
vpc_id = data.aws_vpc.selected.id
ingress {
description = "TLS from VPC"
from_port = 443
to_port = 443
protocol = "tcp"
cidr_blocks = [aws_vpc.main.cidr_block]
}
egress {
from_port = 0
to_port = 0
protocol = "-1"
cidr_blocks = ["0.0.0.0/0"]
}
tags = {
Name = "allow_tls"
}
}
resource "aws_network_interface" "foo" {
subnet_id = aws_subnet.example.id
private_ips = ["172.16.10.100"]
security_groups = [aws_security_group.allow_tls.id]
tags = {
Name = "primary_network_interface"
}
}
resource "aws_instance" "foo" {
ami = "ami-005e54dee72cc1d00" # us-west-2
instance_type = "t2.micro"
network_interface {
network_interface_id = aws_network_interface.foo.id
device_index = 0
}
credit_specification {
cpu_credits = "unlimited"
}
}