Demo of assuming roles so that your Gitlab runner etc can use one account and assume roles and privileges in others

gistfile1.txt

data "aws_caller_identity" "current" {}

locals {
  builder_account_id = "000000000001"    # Where the Builder agents run
  infra_account_id  = "000000000002"    # Where stuff gets built
  distro_account_id = "000000000003"  # Where stuff gets built
}

resource "aws_iam_role" "terraform_role" {
  name = "cross_account_terraform_role"

  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = "sts:AssumeRole"
        Effect = "Allow"
        Principal = {
          AWS = [
            "arn:aws:iam::${local.main_account_id}:root",
            "arn:aws:iam::${data.aws_caller_identity.main.account_id}:root"
          ]
        }
      }
    ]
  })

  tags = {
    Service = "iam"
  }
}

resource "aws_iam_role_policy_attachment" "terraform_role_policy" {
  role       = aws_iam_role.terraform_role.name
  policy_arn = "arn:aws:iam::aws:policy/AdministratorAccess"
}