# Writing Terraform from scratch for every resource
resource "oci_identity_compartment" "prod" { ... }
resource "oci_core_vcn" "main" { ... }
resource "oci_identity_policy" "policies" { ... }
# Result: Unmaintainable, inconsistent, no governance

# Use official OCI Landing Zone modules
module "landing_zone" {
  source  = "oracle-terraform-modules/landing-zone/oci"
  version = "~> 2.0"

  # Infrastructure configuration
  compartments_configuration = { ... }
  network_configuration = { ... }
  security_configuration = { ... }
}

# WRONG - breaks when moving between regions/compartments
resource "oci_core_instance" "web" {
  compartment_id = "ocid1.compartment.oc1..aaaaaa..."  # Hardcoded!
  subnet_id      = "ocid1.subnet.oc1.phx.bbbbbb..."     # Hardcoded!
}

# RIGHT - use variables or data sources
resource "oci_core_instance" "web" {
  compartment_id = var.compartment_ocid
  subnet_id      = data.oci_core_subnet.existing.id
}

# WRONG - orphans boot volumes when instance destroyed ($50+/month per instance)
resource "oci_core_instance" "dev" {
  preserve_boot_volume = true  # Default behavior!
}

# RIGHT - explicit cleanup in dev/test
resource "oci_core_instance" "dev" {
  preserve_boot_volume = false
}

# WRONG - accidental destroy can delete production database
resource "oci_database_autonomous_database" "prod" {
  # No protection!
}

# RIGHT - prevent accidental destruction
resource "oci_database_autonomous_database" "prod" {
  lifecycle {
    prevent_destroy = true
    ignore_changes  = [defined_tags]  # Ignore tag changes from console
  }
}

# WRONG - hardcoded AD breaks multi-region deployment
resource "oci_core_instance" "web" {
  availability_domain = "fMgC:US-ASHBURN-AD-1"  # Tenant-specific!
}

# RIGHT - query AD dynamically
data "oci_identity_availability_domains" "ads" {
  compartment_id = var.tenancy_ocid
}

resource "oci_core_instance" "web" {
  availability_domain = data.oci_identity_availability_domains.ads.availability_domains[0].name
}

# WRONG - no locking, no collaboration
terraform {
  backend "local" {}
}

# RIGHT - use OCI Object Storage with locking
terraform {
  backend "s3" {
    bucket   = "terraform-state"
    key      = "prod/terraform.tfstate"
    region   = "us-phoenix-1"
    endpoint = "https://namespace.compat.objectstorage.us-phoenix-1.oraclecloud.com"

    skip_region_validation      = true
    skip_credentials_validation = true
    skip_metadata_api_check     = true
    use_path_style              = true
  }
}

# WRONG - reordering list recreates ALL resources
resource "oci_core_instance" "web" {
  count = length(var.instance_names)
  display_name = var.instance_names[count.index]
}

# If instance_names changes from ["web1", "web2", "web3"] to ["web0", "web1", "web2", "web3"]
# Terraform RECREATES all instances!

# RIGHT - use for_each with stable keys
resource "oci_core_instance" "web" {
  for_each = toset(var.instance_names)
  display_name = each.value
}

# In provider.tf
provider "oci" {
  auth   = "InstancePrincipal"
  region = var.region
}

# Dynamic group matching rule:
# "ALL {instance.compartment.id = '<compartment-ocid>'}"

# IAM policy:
# "Allow dynamic-group terraform-instances to manage all-resources in tenancy"

Error: 409-Conflict, Resource already exists

# Import existing resource into state
terraform import oci_core_vcn.main ocid1.vcn.oc1.phx.xxxxx

# Then run plan/apply as normal
terraform plan

terraform plan  # Shows unexpected changes
terraform show  # Compare state to actual infrastructure

terraform refresh  # Updates state to match reality

terraform import <resource_type>.<name> <ocid>

lifecycle {
  ignore_changes = [defined_tags, freeform_tags]  # Ignore console tag edits
}

# 1. Make backup
cp terraform.tfstate terraform.tfstate.backup

# 2. Try state repair
terraform state pull > recovered.tfstate
mv recovered.tfstate terraform.tfstate

# 3. If that fails, restore from Object Storage versioning
# Or reconstruct with imports (last resort)

Error: Resource still in use

# 1. Visualize dependencies
terraform graph | dot -Tpng > graph.png

# 2. Destroy in reverse order
terraform destroy -target=oci_core_instance.web
terraform destroy -target=oci_core_subnet.private
terraform destroy -target=oci_core_vcn.main

# Or use depends_on explicitly:
resource "oci_core_vcn" "main" {
  # ...
}

resource "oci_core_subnet" "private" {
  vcn_id = oci_core_vcn.main.id
  # depends_on is implicit via vcn_id reference
}

# Database provisioning takes 15-30 minutes
resource "oci_database_autonomous_database" "prod" {
  # ... configuration ...

  timeouts {
    create = "60m"  # Default 20m often not enough
    update = "60m"
    delete = "30m"
  }
}

# Compute instance usually fast, but can timeout on capacity issues
resource "oci_core_instance" "web" {
  # ... configuration ...

  timeouts {
    create = "30m"  # Allow retries on "out of capacity"
  }
}

# EXPENSIVE - fixed shape
resource "oci_core_instance" "web" {
  shape = "VM.Standard2.4"  # 4 OCPUs, 60GB RAM, $218/month
}

# CHEAPER - flexible shape
resource "oci_core_instance" "web" {
  shape = "VM.Standard.E4.Flex"
  shape_config {
    ocpus         = 4
    memory_in_gbs = 60
  }
  # Cost: (4 × $0.03 + 60 × $0.0015) × 730 = $153/month (30% savings)
}

# Define locals for consistent tagging
locals {
  common_tags = {
    "CostCenter"  = "Engineering"
    "Environment" = var.environment
    "ManagedBy"   = "Terraform"
    "Project"     = var.project_name
  }
}

resource "oci_core_instance" "web" {
  freeform_tags = merge(
    local.common_tags,
    {
      "Component" = "WebServer"
    }
  )
}