08-03-depends_on

Terraform Meta Argument: depends_on

depends_on Meta Argument

• The depends_on Meta Argument in Terraform is used to establish explicit dependencies between resources, specifying that one resource depends on the successful creation or modification of another resource.

• When you set depends_on for a resource, you indicate that this resource should only be created or modified after the resources listed in depends_on are successfully created or modified.

• This is particularly useful when you have resources that rely on the completion of certain tasks before they can proceed.

• Example: You can use depends_on to ensure that elastic ip is assigned to a EC2 web server only after EC2 is created. 1. Create 00_provider.tf for providers 2. Create an AWS EC2 instance using the aws_instance resource block. 3. Create an AWS Elastic IP using the aws_eip resource block. 4. Use the depends_on Meta Argument in the Elastic IP resource to specify that it should only be associated with the EC2 instance once that instance has been created. This ensures that the Elastic IP is associated with a valid EC2 instance.

  00_provider.tf

  terraform {
  required_version = "~> 1.0"
  required_providers {
      aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
      }
  }
  }
  
  provider "aws" {
  region = "us-east-1"
  default_tags {
      tags = {
      Terraform = "yes"
      Project   = "terraform-learning"
      }
  }
  }

  01_ec2.tf

  resource "aws_instance" "my-web-ec2" {
  ami           = "ami-0df435f331839b2d6"
  instance_type = "t2.micro"
  
  tags = {
      Name  = "linux-webserver"
      Owner = "Venkatesh"
  }
  }

  02_eip.tf

  # Resource: aws_eip
  # https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/eip
  
  resource "aws_eip" "my-web-ec2-eip" {
  instance   = aws_instance.my-web-ec2.id
  depends_on = [aws_instance.my-web-ec2]
  }

• Lets Execute Terraform commands to understand resource behavior

  1. terraform init : Initialize terraform
  2. terraform validate : Validate terraform code
  3. terraform fmt : format terraform code
  4. terraform plan : Review the terraform plan
  5. terraform apply : Create Resources by terraform
  • Once terraform completes the execution you should be able to check on your AWS console resources successfully created.

  Cleanup

  6. terraform destroy : destroy or delete Resources, Cleanup the resources we created

     • After you type yes to terraform destroy prompt, terraform will start destroying resources

     • Once terraform completes the execution you should be able to check on your AWS console resources successfully deleted.

References :

Resource: aws_eip
The depends_on Meta-Argument