Error when creating AWS Budget Actions to automatically stop EC2 and RDS

Question

I use one EC2 instance and one RDS to run my Backend for my website. Now I saw that you can create an AWS Budget Action to automatically stop your EC2 or RDS instance. That wasn't possible before and I definitly wanna use it to be 100% sure not to get a fat bill from AWS. I already set up a billing alert, but I want the EC2 and RDS to also be automatically shut down, just to be really safe.

So when creating a new budget in AWS Budgets you can add a "Budget action", which requires you to attach an IAM role to AWS Budgets. I tried that with an existing EC2Role of mine, which has "AmazonEC2FullAccess" Policy attached to it. But this doesn't seem to be the right policy:

Answer 1

Ok I just figured it out after posting the question, the Role also needed a Trust relationship to AWS Budgets, which had to be attached to the Role in IAM:

Answer 2

While creating the role, the first step is to select the trusted entity, where you need to select Budgets

And then select specific permissions related to EC2/RDS and create the role.

NOTE: you will have to create a new role to add this privilege for IAM in the budget.

Answer 3

Just to clarify, after clicking Edit trust relationship, insert this policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Service": "ec2.amazonaws.com"
      },
      "Action": "sts:AssumeRole"
    },
    {
      "Effect": "Allow",
      "Principal": {
        "Service": "budgets.amazonaws.com"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}