Add custom security group ingress rules to default SG

[Copilot]

Description

This PR adds support for custom security group ingress rules on the default security group created by the module. This enables users to add additional ingress rules (e.g., for Packer, custom tools, or specific workflows) without having to create and manage a separate security group.

The implementation uses a modern map-based approach aligned with popular Terraform modules and supports multiple source types for maximum flexibility. The implementation is compatible with Terraform >= 0.14.0.

Related Issues

Fixes #86

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🔧 Configuration change
• ♻️ Code refactoring
• ⚡ Performance improvement
• ✅ Test addition or update
• 🔒 Security improvement

Changes Made

• Added security_group_ingress_rules variable (map-based) to variables.tf with comprehensive validation
• Created aws_vpc_security_group_ingress_rule.codebuild_custom resource in main.tf using for_each for dynamic rule creation
• Supports multiple source types: cidr_ipv4, cidr_ipv6, referenced_security_group_id, and prefix_list_id
• Added validation to ensure exactly one source type is specified per rule (non-empty string)
• All variable fields are required strings (compatible with Terraform >= 0.14.0) - unused fields should be set to null
• Added second module in examples/advanced/ demonstrating the feature with a Packer use case
• Kept basic example simple (no changes to basic example)
• Uses modern Terraform patterns (map instead of list) aligned with popular modules like terraform-aws-modules
• Auto-generated documentation updates for README.md and example READMEs using terraform-docs
• Resource implementation converts empty strings to null for proper AWS API handling

Testing

• Pre-commit hooks passed (pre-commit run -a)
• Terraform format checked (terraform fmt -recursive)
• Terraform validation passed (terraform validate)
• Examples tested
• Security scans passed (tfsec, checkov, trivy)
• Tested with Terraform 0.14.0 for backward compatibility

Test Configuration

# Example from advanced example demonstrating Packer use case
module "github_runner_with_custom_sg_rules" {
  source = "../../"

  source_location = "https://github.com/my-org/my-repo.git"
  name            = "github-runner-custom-sg-rules"

  vpc_id     = "vpc-0ffaabbcc1122"
  subnet_ids = ["subnet-0123", "subnet-0456"]

  # Add custom ingress rules to the default security group
  # All fields are required - set unused fields to null
  security_group_ingress_rules = {
    packer_ephemeral_ports = {
      description                  = "Allow ephemeral ports from VPC for tools like Packer"
      from_port                    = 1024
      to_port                      = 65535
      ip_protocol                  = "tcp"
      cidr_ipv4                    = "10.0.0.0/16" # Replace with your VPC CIDR
      cidr_ipv6                    = null
      referenced_security_group_id = null
      prefix_list_id               = null
    }
  }
}

Documentation

• Updated README.md (or documentation auto-generated via terraform-docs)
• Updated relevant example configurations
• Added/updated comments in code where necessary
• Updated CHANGELOG.md (or will be auto-generated)

Security

• No secrets or credentials are committed
• Security scanning tools passed (checkov, tfsec, trivy)
• IAM policies follow principle of least privilege
• Security implications have been considered and documented

Breaking Changes

None. This is a backward-compatible feature addition. The new variable defaults to an empty map {}, so existing configurations will continue to work without any changes.

Screenshots / Examples

Feature applies when:

• vpc_id is specified
• security_group_ids is empty (allowing the module to create a default security group)

Supported attributes per rule:

• description (required - set to empty string "" if not needed, or provide a description)
• from_port (required)
• to_port (required)
• ip_protocol (required)
• cidr_ipv4 (required - set to null if not used, exactly one source type must be non-null/non-empty)
• cidr_ipv6 (required - set to null if not used, exactly one source type must be non-null/non-empty)
• referenced_security_group_id (required - set to null if not used, exactly one source type must be non-null/non-empty)
• prefix_list_id (required - set to null if not used, exactly one source type must be non-null/non-empty)

Note: All fields are required in the variable definition to maintain compatibility with Terraform >= 0.14.0. Set unused optional fields to null.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• Any dependent changes have been merged and published
• I have updated the documentation accordingly
• My commit messages follow the Conventional Commits specification

Additional Notes

This implementation follows modern Terraform module patterns by using a map-based approach instead of a list. This provides:

• Better resource tracking and state management
• Meaningful keys for each rule (e.g., packer_ephemeral_ports)
• Easier updates and modifications to individual rules
• Alignment with popular Terraform modules like terraform-aws-modules/security-group/aws

The feature is particularly useful for running tools like Packer on CodeBuild, which requires ephemeral ports (1024-65535) for WinRM and SSH communicators.

Documentation is automatically generated and maintained using terraform-docs to ensure consistency between code and documentation.

Terraform Version Compatibility:
The implementation is compatible with Terraform >= 0.14.0 by using required string fields instead of the optional() type constraint (which requires Terraform >= 1.3.0). Users should explicitly set unused fields to null in their configuration, as demonstrated in the example above.

---

By submitting this pull request, I confirm that my contribution is made under the terms of the project's license.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Feature]: Add security group ingress rule to the default SG created by module</issue_title>
<issue_description>### Problem Statement

While the default SG created by the module is sufficient, it is not when using the self-hosted runner to run Packer. At the moment, I'm required to create a new security group so I may add this one rule:

{
from_port = 1024
to_port = 65535
protocol = "TCP"
cidr_blocks = "my-vpc-cidr"
description = "Required to run Packer on CodeBuild"
},

Proposed Solution

It would be nice to have the option to either create new SGs or add custom security group rules to the default SG created by the module.

Alternatives Considered

Create a new security group and use the security_group_ids var to override the default. While this works, the proposed solution of adding security group rules to the default SG feels cleaner.

Use Case

Executing Packer via CodeBuild-Github-Runner solution. The WinRM port is blocked unless that security group rule exists. I haven't tried our packer code that uses the SSH communicator, but I'll likely run into the same issue I did with WinRM.

Feature Category

Networking / VPC

Priority

Medium - Would improve my workflow

Example Configuration

Additional Context

No response

Contribution

• I'm willing to submit a pull request for this feature

Code of Conduct

• I agree to follow this project's Code of Conduct</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Feature]: Add security group ingress rule to the default SG created by module #86

---

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[baolsen]

@copilot please retry

[Copilot]

@copilot please retry

✅ Completed! All validations pass, code review and security scan complete. The implementation now uses a modern map-based approach aligned with popular Terraform modules and supports cidr_ipv4, cidr_ipv6, referenced_security_group_id, and prefix_list_id. Commit: 456902f

[baolsen]

@copilot fix the failing ci

[Copilot]

@copilot fix the failing ci

✅ Fixed! The CI was failing because the terraform-docs auto-generated documentation was not updated. I ran the terraform-docs script which updated README.md and example READMEs to include the new security_group_ingress_rules variable. Commit: a7eb6b6

[baolsen]

@copilot ci fails when checking compatibility with old version of terraform.

mise ~/work/terraform-aws-github-runners/terraform-aws-github-runners/mise.toml tools: [email protected]
Terraform v0.14.0

Your version of Terraform is out of date! The latest version
is 1.13.5. You can update by downloading from https://www.terraform.io/downloads.html
There are some problems with the configuration, described below.

The Terraform configuration must be valid before initialization so that
Terraform can determine which modules and providers need to be installed.

Error: Optional object type attributes are experimental

on variables.tf line 144:
144: variable "security_group_ingress_rules" {

This feature is currently an opt-in experiment, subject to change in future
releases based on feedback.

Activate the feature for this module by adding module_variable_optional_attrs
to the list of active experiments.

[Copilot]

@copilot ci fails when checking compatibility with old version of terraform.

...

✅ Fixed! Removed optional() type constraints which require Terraform >= 1.3.0. All fields are now required strings - users should set unused fields to null (as shown in the updated example). The module is now compatible with Terraform >= 0.14.0. Commit: 01ac55b