Resource Targeting

In this lesson, you'll learn how to use resource targeting with OpenTofu’s plan and apply commands to update individual resources without affecting the rest of your infrastructure.

Example Configuration

Below is a sample HCL configuration that generates a random string and launches an AWS EC2 instance tagged with that string:

resource "random_string" "server-suffix" {
  length  = 6
  upper   = false
  special = false
}

resource "aws_instance" "web" {
  ami           = "ami-06178cf087598769c"
  instance_type = "m5.large"
  tags = {
    Name = "web-${random_string.server-suffix.id}"
  }
}

Applying Changes Normally

If you change the random string’s length from 6 to 5 and run:

$ tofu apply

OpenTofu will plan and apply updates for both resources because the EC2 tag depends on the random string:

Plan: 1 to add, 1 to change, 1 to destroy.

Enter a value: yes
random_string.server-suffix: Destroying... [id=6r923x]
random_string.server-suffix: Creation complete after 0s [id=nglmpo]
aws_instance.web: Modifying... [id=i-67428769e06ae2901]
Apply complete! Resources: 1 added, 1 changed, 1 destroyed.

Targeting a Single Resource

To update only the random string and leave the EC2 instance untouched, use the -target flag:

$ tofu apply -target=random_string.server-suffix

OpenTofu will generate a plan for just that resource:

OpenTofu will perform the following actions:

  # random_string.server-suffix must be replaced
-/+ resource "random_string" "server-suffix" {
    ~ id      = "bl12qd" -> (known after apply)
    ~ length  = 6 -> 5 # forces replacement
}

Plan: 1 to add, 0 to change, 1 to destroy.

Warning: Resource targeting is in effect

Enter a value: yes
random_string.server-suffix: Destroying... [id=6r923x]
random_string.server-suffix: Creation complete after 0s [id=nglmpo]

Warning: Applied changes may be incomplete
Apply complete! Resources: 1 added, 0 changed, 1 destroyed.

CLI Commands Reference

Links and References

• OpenTofu Documentation
• AWS EC2 Overview
• Terraform Random Provider