1.9 : Terraform Lifecycle Rules — Prevent Disasters Before They Happen

🎯 Goal: Go beyond basic resources → use lifecycle rules to build self-healing, zero-downtime, audit-proof infrastructure.

✅ You’ll master:

✅ create_before_destroy → zero-downtime updates

✅ prevent_destroy → stop accidental terraform destroy

✅ ignore_changes → coexist with external tools (ASG, monitoring)

✅ replace_triggered_by → force rebuilds on dependency changes

✅ precondition/postcondition → enforce compliance before & after apply

🧠 Why Lifecycle Rules Matter

❌ Without lifecycle rules:

terraform apply → destroys DB → creates new → 60s downtime

terraform destroy → deletes prod S3 bucket → irrecoverable data loss

ASG scales to 100 → terraform plan → wants to revert to 2 → fighting your tools

✅ With lifecycle rules:

→ Infrastructure that protects itself

→ Zero-downtime deployments by default

→ Safe coexistence with external systems

📦 Lifecycle Rules Cheat Sheet

Rule	Use Case	Risk if Missing	Production Ready?
`create_before_destroy = true`	EC2, RDS, ASG	Downtime during updates	✅ Critical for stateful resources
`prevent_destroy = true`	Prod DBs, S3 buckets, IAM roles	Accidental deletion = outage	✅ Non-negotiable for critical resources
`ignore_changes = [attr]`	ASG `desired_capacity`, EC2 `tags`	Terraform fights external tools	✅ Essential for hybrid infra
`replace_triggered_by = [...]`	Rebuild instances on SG/AMI change	Stale configs, security gaps	✅ Key for immutable infra
`precondition`	Enforce region/tag policies before create	Invalid resources get created	✅ Guardrails for standards
`postcondition`	Verify tags/compliance after create	Deployed resources don’t meet policy	✅ Audit-proof deployments

🎯 Golden Rule:

“If your resource holds data or serves traffic — it needs lifecycle rules.”

✏️ Hands-On: Lifecycle Rules in Action

🔹 `variables.tf` — Setup

variable "allowed_regions" {
  type    = set(string)
  default = ["us-east-1", "us-west-2"]
}

variable "compliance_tags" {
  type    = list(string)
  default = ["Environment", "Compliance", "Owner"]
}

🧠 Why Lifecycle Rules Matter

📦 Lifecycle Rules Cheat Sheet

✏️ Hands-On: Lifecycle Rules in Action

🔹 `variables.tf` — Setup

1️⃣ `create_before_destroy` — Zero-Downtime EC2

`main.tf`

🧠 Why Lifecycle Rules Matter

📦 Lifecycle Rules Cheat Sheet

✏️ Hands-On: Lifecycle Rules in Action

🔹 variables.tf — Setup

1️⃣ create_before_destroy — Zero-Downtime EC2

main.tf

🔹 `variables.tf` — Setup

1️⃣ `create_before_destroy` — Zero-Downtime EC2

`main.tf`