Can Çetin

implicit dependency does not have any keyword but it can be noticed by giving reference to another elements

//implicit dependency via referencing objects
vpc_security_group_ids = [aws_security_group.general.id]

depends_on keyword help us to activate explicit dependency

resource "aws_instance" "my_server_web" {
  ami                    = "ami-0bd39c806c2335b95"
  instance_type          = "t3.micro"
  vpc_security_group_ids = [aws_security_group.general.id]
  tags                   = { Name = "Server-Web" }

  depends_on = [
    aws_instance.my_server_db,
    aws_instance.my_server_app
  ]
}

resource "aws_instance" "my_server_app" {
  ami                    = "ami-0bd39c806c2335b95"
  instance_type          = "t3.micro"
  vpc_security_group_ids = [aws_security_group.general.id]
  tags                   = { Name = "Server-App" }

  depends_on = [aws_instance.my_server_db]
}

resource "aws_instance" "my_server_db" {
  ami                    = "ami-0bd39c806c2335b95"
  instance_type          = "t3.micro"
  vpc_security_group_ids = [aws_security_group.general.id]
  tags                   = { Name = "Server-DB" }
}