1---
2name: terraform-module-library
3description: Build reusable Terraform modules for AWS, Azure, GCP, and OCI infrastructure following infrastructure-as-code best practices. Use when creating infrastructure modules, standardizing cloud provisioning, or implementing reusable IaC components.
4---
5 
6# Terraform Module Library
7 
8Production-ready Terraform module patterns for AWS, Azure, GCP, and OCI infrastructure.
9 
10## Purpose
11 
12Create reusable, well-tested Terraform modules for common cloud infrastructure patterns across multiple cloud providers.
13 
14## When to Use
15 
16- Build reusable infrastructure components
17- Standardize cloud resource provisioning
18- Implement infrastructure as code best practices
19- Create multi-cloud compatible modules
20- Establish organizational Terraform standards
21 
22## Module Structure
23 
24```
25terraform-modules/
26├── aws/
27│   ├── vpc/
28│   ├── eks/
29│   ├── rds/
30│   └── s3/
31├── azure/
32│   ├── vnet/
33│   ├── aks/
34│   └── storage/
35├── gcp/
36│   ├── vpc/
37│   ├── gke/
38│   └── cloud-sql/
39└── oci/
40    ├── vcn/
41    ├── oke/
42    └── object-storage/
43```
44 
45## Standard Module Pattern
46 
47```
48module-name/
49├── main.tf          # Main resources
50├── variables.tf     # Input variables
51├── outputs.tf       # Output values
52├── versions.tf      # Provider versions
53├── README.md        # Documentation
54├── examples/        # Usage examples
55│   └── complete/
56│       ├── main.tf
57│       └── variables.tf
58└── tests/           # Terratest files
59    └── module_test.go
60```
61 
62## AWS VPC Module Example
63 
64**main.tf:**
65 
66```hcl
67resource "aws_vpc" "main" {
68  cidr_block           = var.cidr_block
69  enable_dns_hostnames = var.enable_dns_hostnames
70  enable_dns_support   = var.enable_dns_support
71 
72  tags = merge(
73    {
74      Name = var.name
75    },
76    var.tags
77  )
78}
79 
80resource "aws_subnet" "private" {
81  count             = length(var.private_subnet_cidrs)
82  vpc_id            = aws_vpc.main.id
83  cidr_block        = var.private_subnet_cidrs[count.index]
84  availability_zone = var.availability_zones[count.index]
85 
86  tags = merge(
87    {
88      Name = "${var.name}-private-${count.index + 1}"
89      Tier = "private"
90    },
91    var.tags
92  )
93}
94 
95resource "aws_internet_gateway" "main" {
96  count  = var.create_internet_gateway ? 1 : 0
97  vpc_id = aws_vpc.main.id
98 
99  tags = merge(
100    {
101      Name = "${var.name}-igw"
102    },
103    var.tags
104  )
105}
106```
107 
108**variables.tf:**
109 
110```hcl
111variable "name" {
112  description = "Name of the VPC"
113  type        = string
114}
115 
116variable "cidr_block" {
117  description = "CIDR block for VPC"
118  type        = string
119  validation {
120    condition     = can(regex("^([0-9]{1,3}\\.){3}[0-9]{1,3}/[0-9]{1,2}$", var.cidr_block))
121    error_message = "CIDR block must be valid IPv4 CIDR notation."
122  }
123}
124 
125variable "availability_zones" {
126  description = "List of availability zones"
127  type        = list(string)
128}
129 
130variable "private_subnet_cidrs" {
131  description = "CIDR blocks for private subnets"
132  type        = list(string)
133  default     = []
134}
135 
136variable "enable_dns_hostnames" {
137  description = "Enable DNS hostnames in VPC"
138  type        = bool
139  default     = true
140}
141 
142variable "tags" {
143  description = "Additional tags"
144  type        = map(string)
145  default     = {}
146}
147```
148 
149**outputs.tf:**
150 
151```hcl
152output "vpc_id" {
153  description = "ID of the VPC"
154  value       = aws_vpc.main.id
155}
156 
157output "private_subnet_ids" {
158  description = "IDs of private subnets"
159  value       = aws_subnet.private[*].id
160}
161 
162output "vpc_cidr_block" {
163  description = "CIDR block of VPC"
164  value       = aws_vpc.main.cidr_block
165}
166```
167 
168## Best Practices
169 
1701. **Use semantic versioning** for modules
1712. **Document all variables** with descriptions
1723. **Provide examples** in examples/ directory
1734. **Use validation blocks** for input validation
1745. **Output important attributes** for module composition
1756. **Pin provider versions** in versions.tf
1767. **Use locals** for computed values
1778. **Implement conditional resources** with count/for_each
1789. **Test modules** with Terratest
17910. **Tag all resources** consistently
180 
181**Reference:** See `references/aws-modules.md` and `references/oci-modules.md`
182 
183## Module Composition
184 
185```hcl
186module "vpc" {
187  source = "../../modules/aws/vpc"
188 
189  name               = "production"
190  cidr_block         = "10.0.0.0/16"
191  availability_zones = ["us-west-2a", "us-west-2b", "us-west-2c"]
192 
193  private_subnet_cidrs = [
194    "10.0.1.0/24",
195    "10.0.2.0/24",
196    "10.0.3.0/24"
197  ]
198 
199  tags = {
200    Environment = "production"
201    ManagedBy   = "terraform"
202  }
203}
204 
205module "rds" {
206  source = "../../modules/aws/rds"
207 
208  identifier     = "production-db"
209  engine         = "postgres"
210  engine_version = "15.3"
211  instance_class = "db.t3.large"
212 
213  vpc_id     = module.vpc.vpc_id
214  subnet_ids = module.vpc.private_subnet_ids
215 
216  tags = {
217    Environment = "production"
218  }
219}
220```
221 
222 
223## Testing
224 
225```go
226// tests/vpc_test.go
227package test
228 
229import (
230    "testing"
231    "github.com/gruntwork-io/terratest/modules/terraform"
232    "github.com/stretchr/testify/assert"
233)
234 
235func TestVPCModule(t *testing.T) {
236    terraformOptions := &terraform.Options{
237        TerraformDir: "../examples/complete",
238    }
239 
240    defer terraform.Destroy(t, terraformOptions)
241    terraform.InitAndApply(t, terraformOptions)
242 
243    vpcID := terraform.Output(t, terraformOptions, "vpc_id")
244    assert.NotEmpty(t, vpcID)
245}
246```
247 
248## Related Skills
249 
250- `multi-cloud-architecture` - For architectural decisions
251- `cost-optimization` - For cost-effective designs
252