Terraform – difference between data.aws_iam_policy_document and in-line JSON policy


So I’ve got this block of terraform code, which simply just allow the role to assume role

data "aws_iam_policy_document" "bootstrap_role" {
  statement {
    actions = ["sts:AssumeRole"]

    principals {
      type        = "Service"
      identifiers = ["ec2.amazonaws.com"]
    }
  }
}

resource "aws_iam_role" "bootstrap" {
  name               = "bootstrap-${random_string.bucket.result}"
  assume_role_policy = data.aws_iam_policy_document.bootstrap_role.json
}

When check in AWS Console, I can see following Trust relationships created with:
“Sid”: “”

When I would create the role in AWS Console, I would not have this section:
“Sid”: “”

Tried to update the terraform code to following, and it made no difference:

data "aws_iam_policy_document" "bootstrap_role" {
  statement {
    actions = ["sts:AssumeRole"]

    principals {
      type        = "Service"
      identifiers = ["ec2.amazonaws.com"]
    }

    sid = null
  }
}

resource "aws_iam_role" "bootstrap" {
  name               = "bootstrap-${random_string.bucket.result}"
  assume_role_policy = data.aws_iam_policy_document.bootstrap_role.json
}

After some research, I’ve settled with this code with incline JSON policy instead

resource "aws_iam_role" "bootstrap" {
  name = "bootstrap-${random_string.bucket.result}"
  assume_role_policy = jsonencode(
    {
      "Version" : "2012-10-17",
      "Statement" : [
        {
          "Effect" : "Allow",
          "Principal" : {
            "Service" : "ec2.amazonaws.com"
          },
          "Action" : "sts:AssumeRole"
        }
      ]
    }
  )
}

Now it’s nice and clean


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