Repro attempt for https://github.com/hashicorp/terraform/issues/4186

main.tf

provider "aws" {
  access_key = "foo"
  secret_key = "bar"
  region = "us-east-1"
}

module "vpc" {
  source          = "./tf_aws_vpc"

  name            = "keyprovidertest"
  cidr            = "10.0.0.0/16"
  private_subnets = "10.0.1.0/24"
  public_subnets  = "10.0.101.0/24"
  azs             = ""
}

resource "aws_security_group" "test" {
  vpc_id = "${module.vpc.vpc_id}"
  ingress {
    protocol = "-1"
    from_port = 0
    to_port = 0
    cidr_blocks = ["0.0.0.0/0"]
  }
  egress {
    protocol = "-1"
    from_port = 0
    to_port = 0
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_instance" "test" {
  ami             = "ami-0f8bce65"
  instance_type   = "t2.micro"
  key_name        = "terraform-testing"
  subnet_id       = "${module.vpc.public_subnets}"
  vpc_security_group_ids = ["${aws_security_group.test.id}"]

  provisioner "file" {
    source = "script.sh"
    destination = "/tmp/script.sh"
    connection {
      agent = false
      user = "ubuntu"
      key_file = "~/.ssh/terraform-testing.pem"
    }
  }

  provisioner "remote-exec" {
    inline = [
      "echo 1"
    ]
    connection {
      agent = false
      user = "ubuntu"
      key_file = "~/.ssh/terraform-testing.pem"
    }
  }

  tags {
    Name = "test_server"
  }
}

script.sh

echo 1