Terraform InvalidParameterCombination: DB Security Groups can only be associated with VPC DB Instances

Question

I am trying to provision RDS instance using terraform template and my template looks like this

template.tf

  resource "aws_security_group" "web-server-security"{
  name = "webserver-sg"
  description = "webserver security group"
  ingress {
  from_port = 80
  to_port = 80
  protocol = "tcp"
  cidr_blocks = ["0.0.0.0/0"]
}
tags{
  Name = "web-server-sg"
}

resource "aws_security_group" "db-server-sg" {
  name = "db-server"
  description = "dbserver security group"
  ingress {
  from_port = 3306
  to_port = 3306
  protocol = "tcp"
  security_groups = ["${aws_security_group.web-server-security.id}"]
 }
  tags{
   Name = "db-server-sg"
  }
 }

resource "aws_db_instance" "echomany_db" {
   name = "echomanydb"
   engine = "mysql"
   engine_version = "5.7"
   storage_type = "gp2"
   allocated_storage = 20
   instance_class = "db.t2.micro"
   username = "${var.AWS_DB_USERNAME}"
   password = "${var.AWS_DB_PASSWORD}"
   parameter_group_name = "default.mysql5.7"
   skip_final_snapshot = true
   security_group_names = [
   "${aws_security_group.db-server-sg.id}"
  ]
  tags{
    Name = "db-server"
  }
 }

However i get this following error:

1 error(s) occurred: * aws_db_instance.echomany_db: 1 error(s) occurred:

• aws_db_instance.echomany_db: Error creating DB Instance: InvalidParameterCombination: DB Security Groups can only be associated with VPC DB Instances using API versions 2012-01-15 through 2012-09-17. status code: 400, request id: a19ea8ea-8ea0-46e4-97c6-b946419df9a3

i dont know whats the problem and how to fix this issue.

Answer 1

As mentioned by the documentation vpc_security_group_ids should be used instead of security_group_names which is a deprecated argument.

Answer 2

Parameter named

security_group_names = [ "${aws_security_group.db-server-sg.id}" ]

can only be used while using ec2-classic mode or outside VPC. Use vpc_security_group_ids instead.