depends_on

The depends_on meta-argument, if present, must be a list of references to other resources in the same module.

In this case, you want the DBI server up before the web server starts.

provider "aws" {

  region     = "ap-southeast-1"

  access_key = "AKI"

  secret_key = "vbw"

}

resource "aws_instance" "db" {

   ami = "ami-063e3af9d2cc7fe94"

   instance_type = "t2.micro"

   tags = {

    Name = "Myec2instance"

    ID = "db"

  }

  

}

resource "aws_instance" "web" {

   ami = "ami-063e3af9d2cc7fe94"

   instance_type = "t2.micro"

   

   depends_on = [aws_instance.db]

   tags = {

    Name = "Myec2instance"

    ID = "web"

  }

       

}