How to Provision an AWS EC2 Instance with Terraform

The resource

resource "aws_instance" "web" {
  ami           = "ami-0abcdef1234567890"   # a REAL ami id for your region
  instance_type = "t3.micro"                # a valid type
  tags = { Name = "web" }
}

Two fields do all the work - and both are where applies fail.

Don't hard-code a placeholder AMI

AMI ids are region-specific and change over time, so ami-deadbeef or a copied id from a tutorial will fail. Look up a current one with a data source instead of pasting:

data "aws_ami" "al2023" {
  most_recent = true
  owners      = ["amazon"]
  filter {
    name   = "name"
    values = ["al2023-ami-*-x86_64"]
  }
}

resource "aws_instance" "web" {
  ami           = data.aws_ami.al2023.id    # always a valid, current id
  instance_type = "t3.micro"
}

Use a valid instance type

Instance types follow family + size: t3.micro, t3.small, m5.large. A bad suffix like t2.nano-x isn't a real type and errors on apply. When unsure, t3.micro is a safe, cheap default.

Apply

terraform init
terraform plan      # see exactly what will be created
terraform apply -auto-approve

How to debug

• The error names the field - "InvalidAMIID" (bad/placeholder AMI) or an invalid instance-type message.
• Use the aws_ami data source so the AMI is never stale.
• terraform plan first - confirm the resolved AMI + type before creating anything.

Look up the AMI instead of hard-coding it

A hard-coded AMI id rots: it is region-specific and gets deprecated. Resolve the latest one at plan time with a data source:

data "aws_ami" "ubuntu" {
  most_recent = true
  owners      = ["099720109477"] # Canonical
  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-jammy-22.04-amd64-server-*"]
  }
}

Then reference ami = data.aws_ami.ubuntu.id. Beyond the AMI and instance type, a usable instance needs key_name for SSH access, vpc_security_group_ids to control traffic, subnet_id to place it, and tags so you can find and bill it. Use user_data to run a bootstrap script on first boot. Together these turn a bare instance into one you can actually reach and manage.