Module Inputs / Outputs

Module = function — input variables เข้า, output values ออก — ออกแบบ interface ให้ดี = module ที่ reusable

Inputs (Variables)

Variables ใน module = input parameters

Pattern: Required vs Optional

modules/web-app/variables.tf

# Required (no default)
variable "name" {
  type        = string
  description = "Resource name prefix"
}

variable "vpc_id" {
  type        = string
  description = "VPC ID"
}

# Optional (has default)
variable "instance_type" {
  type        = string
  description = "EC2 instance type"
  default     = "t3.micro"
}

variable "tags" {
  type        = map(string)
  description = "Tags to apply"
  default     = {}
}

Pattern: Object Variables

ใช้ object สำหรับ related parameters:

variable "asg_config" {
  type = object({
    min_size         = number
    max_size         = number
    desired_capacity = number
    instance_type    = string
  })

  default = {
    min_size         = 1
    max_size         = 3
    desired_capacity = 1
    instance_type    = "t3.micro"
  }
}

ใช้:

module "web" {
  source = "./modules/web-app"

  asg_config = {
    min_size         = 2
    max_size         = 10
    desired_capacity = 2
    instance_type    = "t3.large"
  }
}

Pattern: Optional Object Attributes (Terraform 1.3+)

variable "logging" {
  type = object({
    enabled         = bool
    retention_days  = optional(number, 30)
    bucket_name     = optional(string)
  })

  default = {
    enabled = true
  }
}

User ส่งแค่ enabled ก็พอ — retention_days ใช้ default

Pattern: Validation

variable "environment" {
  type = string

  validation {
    condition     = contains(["dev", "staging", "prod"], var.environment)
    error_message = "Environment must be: dev, staging, or prod."
  }
}

variable "instance_count" {
  type    = number
  default = 1

  validation {
    condition     = var.instance_count >= 1 && var.instance_count <= 100
    error_message = "Instance count must be 1-100."
  }
}

Outputs

Output = ค่าที่ module return ให้ caller ใช้

modules/web-app/outputs.tf

output "alb_dns_name" {
  value       = aws_alb.main.dns_name
  description = "ALB DNS name for accessing the application"
}

output "alb_arn" {
  value       = aws_alb.main.arn
  description = "ALB ARN (for IAM policies)"
}

output "asg_name" {
  value       = aws_autoscaling_group.main.name
  description = "Auto Scaling Group name"
}

output "security_group_id" {
  value       = aws_security_group.web.id
  description = "Security group attached to instances"
}

Pattern: Output ทุก Resource ที่อาจ Reference

# ✅ Output ครอบคลุม
output "instance_ids"     { value = aws_instance.web[*].id }
output "instance_arns"    { value = aws_instance.web[*].arn }
output "private_ips"      { value = aws_instance.web[*].private_ip }
output "security_group_id" { value = aws_security_group.web.id }

# ❌ Output น้อยเกิน — caller จะมาขอเพิ่มทีหลัง
output "instance_ids" { value = aws_instance.web[*].id }

Pattern: Computed Outputs

output "url" {
  value       = "https://${aws_alb.main.dns_name}"
  description = "Full URL of the application"
}

output "connection_string" {
  value     = "postgres://${var.username}:${random_password.db.result}@${aws_db_instance.main.endpoint}/${var.db_name}"
  sensitive = true
}

Pattern: Object Outputs

Group related outputs:

output "alb" {
  value = {
    arn       = aws_alb.main.arn
    dns_name  = aws_alb.main.dns_name
    zone_id   = aws_alb.main.zone_id
    listeners = aws_alb_listener.main[*].arn
  }
  description = "ALB details"
}

ใช้:

module "web" {
  source = "./modules/web-app"
  # ...
}

resource "aws_route53_record" "app" {
  zone_id = data.aws_route53_zone.main.zone_id
  name    = "app.example.com"
  type    = "A"

  alias {
    name                   = module.web.alb.dns_name
    zone_id                = module.web.alb.zone_id
    evaluate_target_health = true
  }
}

Pattern: Sensitive Outputs

output "db_password" {
  value     = random_password.db.result
  sensitive = true
}

→ ค่าไม่ปรากฏใน plan/apply log

Pattern: Conditional Outputs

output "load_balancer_dns" {
  value       = var.create_lb ? aws_alb.main[0].dns_name : null
  description = "ALB DNS (null if not created)"
}

ตัวอย่าง: Well-Designed Module Interface

modules/eks-cluster/variables.tf

variable "cluster_name" {
  type        = string
  description = "Name of the EKS cluster"

  validation {
    condition     = can(regex("^[a-zA-Z0-9-]+$", var.cluster_name))
    error_message = "Cluster name must be alphanumeric with hyphens."
  }
}

variable "kubernetes_version" {
  type        = string
  description = "Kubernetes version (e.g., 1.30)"
  default     = "1.30"
}

variable "vpc_config" {
  type = object({
    vpc_id     = string
    subnet_ids = list(string)
  })
  description = "VPC configuration for cluster"
}

variable "node_groups" {
  type = map(object({
    instance_types = list(string)
    desired_size   = number
    min_size       = number
    max_size       = number
    capacity_type  = optional(string, "ON_DEMAND")
    disk_size      = optional(number, 20)
    labels         = optional(map(string), {})
    taints = optional(list(object({
      key    = string
      value  = string
      effect = string
    })), [])
  }))

  description = "Map of node group configurations"
  default     = {}
}

variable "enable_irsa" {
  type        = bool
  description = "Enable IAM Roles for Service Accounts"
  default     = true
}

variable "tags" {
  type        = map(string)
  description = "Tags to apply to all resources"
  default     = {}
}

modules/eks-cluster/outputs.tf

output "cluster_id" {
  value       = aws_eks_cluster.main.id
  description = "Cluster ID"
}

output "cluster_endpoint" {
  value       = aws_eks_cluster.main.endpoint
  description = "Cluster API endpoint"
}

output "cluster_ca_certificate" {
  value       = aws_eks_cluster.main.certificate_authority[0].data
  description = "Cluster CA certificate (base64)"
  sensitive   = true
}

output "cluster_security_group_id" {
  value       = aws_eks_cluster.main.vpc_config[0].cluster_security_group_id
  description = "Cluster security group"
}

output "node_groups" {
  value = {
    for k, v in aws_eks_node_group.this : k => {
      arn      = v.arn
      status   = v.status
      capacity = v.scaling_config[0]
    }
  }
  description = "Node groups summary"
}

output "oidc_provider_arn" {
  value       = var.enable_irsa ? aws_iam_openid_connect_provider.this[0].arn : null
  description = "OIDC provider ARN for IRSA"
}

output "kubeconfig_command" {
  value       = "aws eks update-kubeconfig --name ${aws_eks_cluster.main.name} --region ${data.aws_region.current.name}"
  description = "Run this command to update kubeconfig"
}

Best Practices

Variables

✅ DO:
- Description ทุกตัว
- Validation rules ที่ make sense
- Default ที่ sensible สำหรับ optional
- Type ที่ specific (อย่าใช้ any)
- Group related vars เป็น object

❌ DON'T:
- ห้ามมี variable ที่ไม่ใช้
- ห้ามใช้ name สั้นเกิน (`x`, `count`, `name`)
- ห้าม default ที่ require change ใน production

Outputs

✅ DO:
- Output ทุก attribute ที่ caller อาจใช้
- Description ทุก output
- Sensitive marker สำหรับ secrets
- Computed values (URL, connection string)
- Object outputs สำหรับ related fields

❌ DON'T:
- ห้าม output ค่าที่หา reference ตรงๆ ได้ง่าย
- ห้าม output ทุก attribute (เลือกที่ค่ามาก)

ตัวอย่าง: API Design Comparison

❌ Bad Interface

module "thing" {
  source = "./modules/thing"

  x  = "abc"
  y  = 5
  z  = true
  config = "{...}"   # JSON string!
}

✅ Good Interface

module "thing" {
  source = "./modules/thing"

  name             = "my-app"
  instance_count   = 5
  enable_logging   = true

  database_config = {
    engine           = "postgres"
    instance_class   = "db.t3.micro"
    backup_retention = 7
  }

  tags = {
    Environment = "production"
  }
}

สรุป

• Inputs = variable block — required, optional, validated
• Outputs = output block — descriptive, sensitive-aware, computed
• ใช้ object types สำหรับ related parameters
• Optional attributes (1.3+) ลด boilerplate
• Document ทุก variable + output
• Sensible defaults ให้ optional vars
• Output ครอบคลุม ทุก attribute ที่ caller อาจใช้

ต่อไป → Module Best Practices