Terraform Data Source

In simple words Terraform Data Source is:

• Bridge between “Terraform-created” and “non-Terraform-created” infrastructure
• A Terraform data source lets you query or fetch existing information from outside Terraform so you can use it inside your Terraform configuration.

Let me give an example:

• Let's say you have an existing VPC created but not managed by terraform, now you want to create a EC2 in that VPC, so you need the VPC info, in such scenario you can use Data Source.

• Also when value of particular resource changes dynamically, like AMI id, we can use Data Source

One thing to remember about Data Source

• using Data Source we cannot create resources.
• we can reference existing resources, fetch dynamic info.

Example

• using existing VPC configuration

data "aws_vpc" "main" {
  filter {
    name   = "tag:Name"
    values = ["main-vpc"]
  }
}

resource "aws_subnet" "app" {
  vpc_id = data.aws_vpc.main.id
}

• Getting latest AMI id

data "aws_vpc" "main" {
  filter {
    name   = "tag:Name"
    values = ["main-vpc"]
  }
}

resource "aws_subnet" "app" {
  vpc_id = data.aws_vpc.main.id
}

Benifits of using Data Source

• Eleminating of HardCoding.
• Enable modular, resuable code

Video: