How to fix Error: replace_triggered_by argument is invalid in Terraform

The replace_triggered_by argument was introduced in Terraform 1.2. Check your version:

terraform version

If you're using an older version, upgrade Terraform to at least 1.2:

# Using tfenv (recommended)
tfenv install 1.2.0
tfenv use 1.2.0

# Or download from https://www.terraform.io/downloads

Ensure the referenced resource exists and is a managed resource (not a variable or data source). List all resources in your configuration:

terraform state list

Verify the resource name matches exactly. Common mistakes:
- Typos in resource type or name
- Using aws_instance instead of just the resource reference
- Referencing a deleted or commented-out resource

Only managed resources can be referenced. This is INVALID:

resource "aws_instance" "example" {
  lifecycle {
    # WRONG: referencing a variable
    replace_triggered_by = [var.ami_version]

    # WRONG: referencing a data source
    replace_triggered_by = [data.aws_ami.latest]

    # WRONG: referencing a local value
    replace_triggered_by = [local.instance_config]
  }
}

This is CORRECT:

resource "aws_instance" "example" {
  lifecycle {
    # RIGHT: referencing managed resources
    replace_triggered_by = [
      aws_security_group.default,
      aws_ami.ubuntu
    ]
  }
}

If you need to trigger replacements based on variable changes, use the terraform_data resource as an intermediary:

resource "terraform_data" "ami_version" {
  input = var.ami_version
}

resource "aws_instance" "example" {
  ami = data.aws_ami.latest.id

  lifecycle {
    replace_triggered_by = [terraform_data.ami_version]
  }
}

This works because terraform_data is a managed resource that Terraform tracks for planned changes.

Check for syntax errors in your resource references:

terraform validate

The output will highlight exactly which resource reference is invalid. Common syntax errors:
- Missing resource type: aws_sg instead of aws_security_group.example
- Including brackets: [aws_instance.example.id] instead of [aws_instance.example]
- Using string literals: ["aws_instance.example"] instead of [aws_instance.example]

Ensure that adding replace_triggered_by doesn't create a dependency cycle. For example, if Resource A depends on Resource B, and you make Resource B's replacement depend on Resource A, Terraform cannot resolve the order:

# BAD: Creates a cycle
resource "aws_instance" "app" {
  security_groups = [aws_security_group.app.id]  # A depends on B

  lifecycle {
    replace_triggered_by = [aws_security_group.app]  # B depends on A
  }
}

Use terraform_data or restructure dependencies to break the cycle.