13 TF Replace + Provisioners

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🔁 -replace (Modern alternative to taint)

• Forces destroy + recreate of a resource in the same apply run ✔
• Change appears in plan as -/+ before execution ✔
• Safer & explicit than taint 💡
• Works without manually modifying state 📌

🛠 Command

terraform apply -replace="aws_instance.app"

📊 Plan output will show

# aws_instance.app will be replaced
-/+ destroy and then create

When to use 💡

1️⃣ Resource is corrupted (EC2, DB, etc.)
2️⃣ Provisioner left system in bad state
3️⃣ Want a fresh instance without touching config

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🧰 Terraform Provisioners

📌 Definition

• Run scripts/commands after resource creation
• Not recommended for regular use (final option) ⚠

🔁 Types

1️⃣ local-exec → Runs on Terraform host machine ✔

resource "aws_instance" "web" {
  ami           = "ami-0c02fb55956c7d316" # Amazon Linux 2
  instance_type = "t2.micro"
 
  provisioner "local-exec" {
    command = "echo 'EC2 Created: ${self.public_ip}' >> ec2.log"
  }
}

2️⃣ remote-exec → Runs on remote server via SSH/WinRM ✔

resource "aws_instance" "web3" {
  ami           = "ami-0c02fb55956c7d316"
  instance_type = "t2.micro"
 
  connection {
    type        = "ssh"
    user        = "ec2-user"
    private_key = file("~/.ssh/id_rsa")
    host        = self.public_ip
  }
 
  provisioner "remote-exec" {
    inline = [
      "chmod +x /tmp/install.sh",
      "sudo /tmp/install.sh",
      "sudo systemctl start nginx"
    ]
  }
}

3️⃣ file → Copies file to remote server ✔

resource "aws_instance" "web2" {
  ami           = "ami-0c02fb55956c7d316"
  instance_type = "t2.micro"
 
  connection {
    type        = "ssh"
    user        = "ec2-user"
    private_key = file("~/.ssh/id_rsa")
    host        = self.public_ip
  }
 
  provisioner "file" {
    source      = "install.sh"
    destination = "/tmp/install.sh"
  }
}

🔌 Connection (only used by remote/file)

  connection {
    type        = "ssh"
    user        = "ec2-user"
    private_key = file("~/.ssh/id_rsa")
    host        = self.public_ip
  }

⚙ Options

• when = create (default) ✔
• on_failure = continue ✔ (doesn’t break apply)
• on_failure = fail ❌ (stops apply)

⚠ Key Notes

• If provisioner fails → resource still saved in state
• On resource replace (-/+) → provisioner runs again
• Better alternatives: EC2 User Data, Ansible, CI/CD scripts 💡

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