terraform/website/docs/language/meta-arguments/depends_on.html.md

layout	page_title	description
language	The depends_on Meta-Argument - Configuration Language	Using the Terraform language `depends_on` meta-argument to handle hidden resource or module dependencies.

The depends_on Meta-Argument

-> Version note: Module support for depends_on was added in Terraform 0.13, and previous versions can only use it with resources.

Use the depends_on meta-argument to handle hidden resource or module dependencies that Terraform can't automatically infer.

Explicitly specifying a dependency is only necessary when a resource or module relies on some other resource's behavior but doesn't access any of that resource's data in its arguments.

This argument is available in module blocks and in all resource blocks, regardless of resource type. For example:

resource "aws_iam_role" "example" {
  name = "example"

  # assume_role_policy is omitted for brevity in this example. See the
  # documentation for aws_iam_role for a complete example.
  assume_role_policy = "..."
}

resource "aws_iam_instance_profile" "example" {
  # Because this expression refers to the role, Terraform can infer
  # automatically that the role must be created first.
  role = aws_iam_role.example.name
}

resource "aws_iam_role_policy" "example" {
  name   = "example"
  role   = aws_iam_role.example.name
  policy = jsonencode({
    "Statement" = [{
      # This policy allows software running on the EC2 instance to
      # access the S3 API.
      "Action" = "s3:*",
      "Effect" = "Allow",
    }],
  })
}

resource "aws_instance" "example" {
  ami           = "ami-a1b2c3d4"
  instance_type = "t2.micro"

  # Terraform can infer from this that the instance profile must
  # be created before the EC2 instance.
  iam_instance_profile = aws_iam_instance_profile.example

  # However, if software running in this EC2 instance needs access
  # to the S3 API in order to boot properly, there is also a "hidden"
  # dependency on the aws_iam_role_policy that Terraform cannot
  # automatically infer, so it must be declared explicitly:
  depends_on = [
    aws_iam_role_policy.example,
  ]
}

The depends_on meta-argument, if present, must be a list of references to other resources or child modules in the same calling module. Arbitrary expressions are not allowed in the depends_on argument value, because its value must be known before Terraform knows resource relationships and thus before it can safely evaluate expressions.

The depends_on argument should be used only as a last resort. When using it, always include a comment explaining why it is being used, to help future maintainers understand the purpose of the additional dependency.