How to create aws_instance with existing VPC?

user_587467 0
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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)

terraform amazon-web-services
3 Answers

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...
}
user_38521260

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).

user_2714150

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"
  }
}
user_22463450
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