How to Ignore Change of an Attribute in Terraform Blocks

TLDR

To ignore changes to a specific attribute in Terraform, use the lifecycle block with the ignore_changes argument. This is useful for attributes managed outside of Terraform or for temporary overrides.

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Terraform's lifecycle block allows you to control how resources are managed. The ignore_changes argument is particularly useful for ignoring changes to specific attributes, such as those managed by external systems or temporary overrides.

Why Ignore Changes?

• External Management: Some attributes are managed outside of Terraform, such as by a cloud provider or another tool.
• Temporary Overrides: Ignore changes to attributes that are temporarily modified.
• Avoid Unnecessary Updates: Prevent Terraform from overwriting changes made outside of its control.

Using ignore_changes

The ignore_changes argument is part of the lifecycle block. You can specify one or more attributes to ignore.

Example: Ignoring a Single Attribute

resource "azurerm_virtual_machine" "example" {
  name                  = "example-vm"
  location              = azurerm_resource_group.example.location
  resource_group_name   = azurerm_resource_group.example.name
  network_interface_ids = [azurerm_network_interface.example.id]
  vm_size               = "Standard_DS1_v2"

  lifecycle {
    ignore_changes = ["vm_size"]
  }
}

In this example, changes to the vm_size attribute are ignored.

Example: Ignoring Multiple Attributes

Here's how to ignore multiple attributes:

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
  tags = {
    Name = "example-instance"
  }

  lifecycle {
    ignore_changes = ["tags[\"Name\"]", "instance_type"]
  }
}

In this example, changes to the Name tag and instance_type are ignored.

Best Practices

• Use Sparingly: Only ignore changes when absolutely necessary to avoid configuration drift.
• Document Reasons: Clearly document why changes are being ignored.
• Monitor Resources: Regularly review ignored attributes to ensure they are still relevant.

By using the ignore_changes argument, you can manage resources more flexibly in Terraform, avoiding unnecessary updates and conflicts.