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The ec2-instance module is a general-purpose building block that the root configuration instantiates three times — once for each of the two Node.js servers (node_1, node_2) and once for the MongoDB database (mongodb). Each call passes different subnet IDs, security groups, public IP settings, and user-data scripts, producing three distinct instances from a single module definition. Shared concerns — IMDSv2 enforcement, encrypted storage, IAM profile attachment — are configured once inside the module and apply uniformly to all three instances.

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EC2 Resource Configuration

The aws_instance resource inside this module is configured with several security and operational defaults:
  • AMI: Sourced from data.aws_ami.ubuntu, which resolves to the latest Ubuntu 24.04 LTS (ubuntu/images/hvm-ssd-gp3/ubuntu-noble-24.04-amd64-server-*) owned by Canonical.
  • User data: Loaded from file(var.user_data_file). The user_data_replace_on_change = true flag forces EC2 to replace the instance (not just re-run user-data) whenever the bootstrap script changes, ensuring the instance always reflects the current script.
  • IMDSv2 enforced: metadata_options sets http_tokens = "required", blocking all requests to the Instance Metadata Service that do not use session-oriented IMDSv2. This prevents SSRF attacks from leaking instance credentials.
  • Root volume: gp3 type, 20 GB default, encrypted = true. The gp3 baseline of 3,000 IOPS is included at no extra cost.
  • Monitoring: monitoring = false — basic CloudWatch metrics only; detailed (1-minute) monitoring is not enabled.

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Input Variables

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name
string
required
Value for the instance’s Name tag (e.g. terraform-mean-node-1). Constructed in the root module as "${var.project_name}-node-1".
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ami_id
string
required
The AMI ID to launch. In the root module this is always data.aws_ami.ubuntu.id, resolving to the latest Ubuntu 24.04 LTS AMI in the target region.
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instance_type
string
required
EC2 instance type (e.g. t3.micro, t3.small). The same var.instance_type from the root is used for all three instances.
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subnet_id
string
required
The subnet in which to launch the instance. node_1 uses public_subnet_1_id, node_2 uses public_subnet_2_id, and mongodb uses private_subnet_id.
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security_group_ids
list(string)
required
List of security group IDs to attach to the instance. Node instances receive [node_security_group_id]; the MongoDB instance receives [mongo_security_group_id].
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associate_public_ip
bool
required
Whether to assign a public IP address. Set to true for node_1 and node_2 (public subnets); set to false for mongodb (private subnet).
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key_name
string
required
The name of the EC2 Key Pair to associate with the instance. Sourced from module.keypair.key_name in the root module.
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iam_instance_profile
string
required
The name of the IAM instance profile to attach. Sourced from module.iam.instance_profile_name, granting all instances SSM access.
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user_data_file
string
required
Filesystem path to the shell script run on first boot (e.g. ${path.root}/userdata/node.sh or ${path.root}/userdata/mongo.sh). The script content is read with Terraform’s file() function.
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volume_size
number
default:"20"
Size of the root EBS volume in gigabytes. Defaults to 20. The volume type is always gp3 and encryption is always enabled regardless of this value.

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Outputs

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instance_id
string
The EC2 instance ID (e.g. i-0abc123def456). The alb module consumes node_1 and node_2 instance IDs via the target_instances map.
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private_ip
string
The private IPv4 address of the instance. Available for all three instances regardless of subnet type.
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public_ip
string
The public IPv4 address of the instance. Returns a valid address for node_1 and node_2; returns null for mongodb since associate_public_ip = false.
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private_dns
string
The private DNS hostname (e.g. ip-10-0-1-42.ec2.internal). Useful for service-to-service communication inside the VPC, such as Node.js connecting to MongoDB.

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Three Module Calls Compared

The root main.tf invokes ec2-instance three times. The key differences between calls are highlighted in comments: 
# ── node_1: public subnet A, public IP, node bootstrap ───────────────────────
module "node_1" {
  source               = "./modules/ec2-instance"
  name                 = "${var.project_name}-node-1"
  ami_id               = data.aws_ami.ubuntu.id
  instance_type        = var.instance_type
  subnet_id            = module.network.public_subnet_1_id   # public AZ1
  security_group_ids   = [module.security.node_security_group_id]
  associate_public_ip  = true                                # public IP
  key_name             = module.keypair.key_name
  iam_instance_profile = module.iam.instance_profile_name
  user_data_file       = "${path.root}/userdata/node.sh"     # node script
}

# ── node_2: public subnet B, public IP, node bootstrap ───────────────────────
module "node_2" {
  source               = "./modules/ec2-instance"
  name                 = "${var.project_name}-node-2"
  ami_id               = data.aws_ami.ubuntu.id
  instance_type        = var.instance_type
  subnet_id            = module.network.public_subnet_2_id   # public AZ2
  security_group_ids   = [module.security.node_security_group_id]
  associate_public_ip  = true                                # public IP
  key_name             = module.keypair.key_name
  iam_instance_profile = module.iam.instance_profile_name
  user_data_file       = "${path.root}/userdata/node.sh"     # node script
}

# ── mongodb: private subnet, no public IP, mongo bootstrap ───────────────────
module "mongodb" {
  source               = "./modules/ec2-instance"
  name                 = "${var.project_name}-mongodb"
  ami_id               = data.aws_ami.ubuntu.id
  instance_type        = var.instance_type
  subnet_id            = module.network.private_subnet_id    # private AZ1
  security_group_ids   = [module.security.mongo_security_group_id]
  associate_public_ip  = false                               # no public IP
  key_name             = module.keypair.key_name
  iam_instance_profile = module.iam.instance_profile_name
  user_data_file       = "${path.root}/userdata/mongo.sh"    # mongo script
}
To increase the MongoDB volume to 50 GB without affecting the Node.js instances, add volume_size = 50 only to the mongodb module call. The default of 20 GB continues to apply to node_1 and node_2.

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