1.8 : Terraform Meta-Arguments — Control Flow for Infrastructure

🎯 Goal: Move beyond basic resources → use meta-arguments to build dynamic, reliable, production-grade configs.

✅ You’ll master:

✅ count vs for_each: When & why to use each

✅ depends_on: Explicit dependencies (no more “race conditions”)

✅ lifecycle: Protect critical resources (prevent_destroy, create_before_destroy)

✅ Real-world patterns (S3 buckets, IAM users, multi-region)

🧠 Why Meta-Arguments Matter

❌ Without meta-arguments:

→ 10 copies of aws_s3_bucket blocks

→ Resource creation order = guesswork

→ Accidental terraform destroy = production outage

✅ With meta-arguments:

→ DRY: One block → N resources

→ Reliable: Control dependencies & lifecycle

→ Safe: Guardrails against human error

📦 Meta-Arguments Cheat Sheet

Meta-Argument	Input Type	Use Case	Stability	Production Ready?
`count`	`number`	Fixed N identical resources (e.g., dev instances)	⚠️ Low (index drift)	❌ Avoid in prod
`for_each`	`map` / `set(string)`	Named resources (e.g., env-specific buckets)	✅ High (key-based)	✅ Preferred
`depends_on`	`[resource]`	Hidden dependencies (e.g., IAM → S3)	—	✅ Use sparingly
`lifecycle`	Block	Protect resources, ignore drift	—	✅ Critical for prod

🎯 Golden Rule:

“Use for_each 90% of the time — count only for simple, temporary resources.”

✏️ Hands-On: `count` vs `for_each` — S3 Bucket Lab

🔹 `variables.tf` — Input Data

# 🔸 List (for `count`)
variable "bucket_names_list" {
  type    = list(string)
  default = ["dev-logs", "staging-logs"]
}

# 🔸 Set (for `for_each`)
variable "bucket_names_set" {
  type = set(string)
  default = toset(["prod-logs", "dr-logs"])  # ← Dedupes automatically
}

# 🔸 Map (for advanced `for_each`)
variable "bucket_configs" {
  type = map(object({
    tags  = map(string)
    acl   = string
  }))
  default = {
    "audit" = {
      tags = { Purpose = "Compliance" },
      acl  = "private"
    }
    "backup" = {
      tags = { Purpose = "Disaster Recovery" },
      acl  = "private"
    }
  }
}

🧠 Why Meta-Arguments Matter

📦 Meta-Arguments Cheat Sheet

✏️ Hands-On: `count` vs `for_each` — S3 Bucket Lab

🔹 `variables.tf` — Input Data

1️⃣ `count` — Simple, but Fragile

`main.tf`

🧠 Why Meta-Arguments Matter

📦 Meta-Arguments Cheat Sheet

✏️ Hands-On: count vs for_each — S3 Bucket Lab

🔹 variables.tf — Input Data

1️⃣ count — Simple, but Fragile

main.tf

✏️ Hands-On: `count` vs `for_each` — S3 Bucket Lab

🔹 `variables.tf` — Input Data

1️⃣ `count` — Simple, but Fragile

`main.tf`