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Terraform Version

subnet

This module manages Oracle Cloud Infrastructure (OCI) Subnets. A subnet is a subdivision of a Virtual Cloud Network (VCN) that contains a contiguous range of IP addresses. Subnets enable you to group related resources and apply network policies at a granular level.

Key concepts:

  • Hierarchical relationship: VCN → Subnet → Resources
  • Public vs Private subnets: Controlled by prohibit_public_ip_on_vnic parameter
  • Route Tables: Control traffic routing between subnets and to external networks
  • Security Lists: Stateful firewall rules at the subnet level
  • Network Security Groups (NSG): Stateful firewall rules at the instance level
  • Regional vs AD-specific: Subnets can be regional or tied to a specific Availability Domain
  • CIDR rules: Subnet CIDR must be within VCN CIDR and not overlap with other subnets
  • DNS integration: DNS labels enable FQDN resolution for instances

Important considerations:

  • Each subnet must have a unique CIDR block within its VCN
  • Subnets can be associated with route tables and security lists
  • Network Security Groups provide additional security at the instance level
  • Regional subnets span all Availability Domains in the region
  • AD-specific subnets are tied to a single Availability Domain

Usage

Usage

This document provides examples of how to use the subnet module.

Example 1: Basic Subnet

module "subnet" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id = "ocid1.compartment.oc1..example"
  vcn_id         = "ocid1.vcn.oc1..example"
  cidr_block     = "10.0.1.0/24"
  display_name   = "my-subnet"

  module_enabled = true
}

Example 2: Public Subnet

module "public_subnet" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id             = "ocid1.compartment.oc1..example"
  vcn_id                     = "ocid1.vcn.oc1..example"
  cidr_block                 = "10.0.2.0/24"
  display_name               = "public-subnet"
  prohibit_public_ip_on_vnic = false  # Allow public IPs

  module_enabled = true
}

Example 3: Private Subnet

module "private_subnet" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id             = "ocid1.compartment.oc1..example"
  vcn_id                     = "ocid1.vcn.oc1..example"
  cidr_block                 = "10.0.3.0/24"
  display_name               = "private-subnet"
  prohibit_public_ip_on_vnic = true  # Prohibit public IPs (default)

  module_enabled = true
}

Example 4: Subnet with Route Table

module "subnet_with_route_table" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id = "ocid1.compartment.oc1..example"
  vcn_id         = "ocid1.vcn.oc1..example"
  cidr_block     = "10.0.4.0/24"
  display_name   = "subnet-with-route"
  route_table_id = "ocid1.routetable.oc1..example"

  module_enabled = true
}

Example 5: Subnet with Security Lists

module "subnet_with_security_lists" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id    = "ocid1.compartment.oc1..example"
  vcn_id            = "ocid1.vcn.oc1..example"
  cidr_block        = "10.0.5.0/24"
  display_name      = "subnet-with-security"
  security_list_ids = [
    "ocid1.securitylist.oc1..example1",
    "ocid1.securitylist.oc1..example2"
  ]

  module_enabled = true
}

Example 6: Subnet with DNS Label

module "subnet_with_dns" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id = "ocid1.compartment.oc1..example"
  vcn_id         = "ocid1.vcn.oc1..example"
  cidr_block     = "10.0.6.0/24"
  display_name   = "dns-subnet"
  dns_label      = "appsubnet"

  module_enabled = true
}

Example 7: Using Subnet Output in Compute Module

module "subnet_for_compute" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id = "ocid1.compartment.oc1..example"
  vcn_id         = "ocid1.vcn.oc1..example"
  cidr_block     = "10.0.7.0/24"
  display_name   = "compute-subnet"

  module_enabled = true
}

module "compute_instance" {
  source = "github.com/hadenlabs/terraform-oci//modules/compute"

  compartment_id      = "ocid1.compartment.oc1..example"
  availability_domain = "us-ashburn-1"
  shape               = "VM.Standard.E4.Flex"
  subnet_id           = module.subnet_for_compute.subnet_id  # Using subnet output
  display_name        = "my-instance"
  image_id            = "ocid1.image.oc1..example"
  ssh_public_key      = "ssh-rsa AAAAB3NzaC1yc2E..."

  module_enabled = true
}

Example 8: Dynamic module_enabled

module "conditional_subnet" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id = "ocid1.compartment.oc1..example"
  vcn_id         = "ocid1.vcn.oc1..example"
  cidr_block     = "10.0.8.0/24"
  display_name   = "conditional-subnet"

  # Enable subnet only in production environment
  module_enabled = var.environment == "production"
}

Example 9: Subnet with Tags

module "subnet_with_tags" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id = "ocid1.compartment.oc1..example"
  vcn_id         = "ocid1.vcn.oc1..example"
  cidr_block     = "10.0.9.0/24"
  display_name   = "tagged-subnet"

  freeform_tags = {
    Environment = "Production"
    Department  = "Engineering"
    Project     = "Terraform-OCI"
  }

  defined_tags = {
    "Oracle-Tags.CreatedBy" = "terraform"
    "Oracle-Tags.CreatedOn" = "2024-01-01"
  }

  module_enabled = true
}

Example 10: Availability Domain Specific Subnet

module "ad_specific_subnet" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id      = "ocid1.compartment.oc1..example"
  vcn_id              = "ocid1.vcn.oc1..example"
  cidr_block          = "10.0.10.0/24"
  display_name        = "ad-subnet"
  availability_domain = "us-ashburn-1-AD-1"  # Specific AD

  module_enabled = true
}

Example 11: Complete Configuration

module "complete_subnet" {
  source = "github.com/hadenlabs/terraform-oci//modules/subnet"

  compartment_id             = "ocid1.compartment.oc1..example"
  vcn_id                     = "ocid1.vcn.oc1..example"
  cidr_block                 = "10.0.11.0/24"
  display_name               = "complete-subnet"
  availability_domain        = "us-ashburn-1-AD-1"
  route_table_id             = "ocid1.routetable.oc1..example"
  security_list_ids          = ["ocid1.securitylist.oc1..example"]
  prohibit_public_ip_on_vnic = false
  dns_label                  = "complete"

  freeform_tags = {
    Environment = "Development"
    Owner       = "DevOps"
  }

  defined_tags = {
    "Oracle-Tags.CreatedBy" = "terraform-module"
  }

  module_enabled = true
}

Requirements

Name Version
terraform >= 1.0.0
oci >= 4.67.3

Providers

Name Version
oci 8.3.0

Modules

No modules.

Resources

Name Type
oci_core_subnet.this resource
oci_identity_availability_domains.this data source

Inputs

Name Description Type Default Required
availability_domain The availability domain for the subnet. If not specified, the subnet will be regional. string null no
cidr_block The CIDR block for the subnet. Must be a valid CIDR within the VCN's CIDR range and not overlap with other subnets in the same VCN. string n/a yes
compartment_id The OCID of the compartment string n/a yes
defined_tags Defined tags for the subnet map(string) {} no
display_name The display name of the subnet string n/a yes
dns_label A DNS label for the subnet, used in conjunction with the VNIC's hostname and VCN's DNS label to form a fully qualified domain name (FQDN) for instances in this subnet string null no
freeform_tags Freeform tags for the subnet map(string) {} no
module_enabled (Optional) Whether to create resources within the module or not. Default is true. bool true no
prohibit_public_ip_on_vnic Whether to prohibit public IP addresses on VNICs in this subnet. Set to true for private subnets, false for public subnets. bool true no
route_table_id The OCID of the route table to associate with the subnet string null no
security_list_ids List of security list OCIDs to associate with the subnet list(string) [] no
vcn_id The OCID of the VCN string n/a yes

Outputs

Name Description
availability_domain The availability domain of the subnet
cidr_block The CIDR block of the subnet
compartment_id The OCID of the compartment containing the subnet
defined_tags The defined tags of the subnet
display_name The display name of the subnet
dns_label The DNS label of the subnet
freeform_tags The freeform tags of the subnet
module_enabled (Optional) Whether to create resources within the module or not. Default is true.
prohibit_public_ip_on_vnic Whether public IP addresses are prohibited on VNICs in this subnet
route_table_id The OCID of the route table associated with the subnet
security_list_ids List of security list OCIDs associated with the subnet
state The current state of the subnet
subnet_id The OCID of the created subnet
time_created The date and time the subnet was created
vcn_id The OCID of the VCN containing the subnet
virtual_router_ip The IP address of the virtual router for the subnet
virtual_router_mac The MAC address of the virtual router for the subnet

Help

Got a question?

File a GitHub issue.

Contributing

See Contributing.

Module Versioning

This Module follows the principles of Semantic Versioning (SemVer).

Using the given version number of MAJOR.MINOR.PATCH, we apply the following constructs:

  1. Use the MAJOR version for incompatible changes.
  2. Use the MINOR version when adding functionality in a backwards compatible manner.
  3. Use the PATCH version when introducing backwards compatible bug fixes.

Backwards compatibility in 0.0.z and 0.y.z version

  • In the context of initial development, backwards compatibility in versions 0.0.z is not guaranteed when z is increased. (Initial development)
  • In the context of pre-release, backwards compatibility in versions 0.y.z is not guaranteed when y is increased. (Pre-release)

Copyright

Copyright © 2018-2026 Hadenlabs

Trademarks

All other trademarks referenced herein are the property of their respective owners.

License

The code and styles are licensed under the LGPL-3.0 license See project license..

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