> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Resource Attributes And Dependencies

> This article explores how OpenTofu records resource attributes and manages dependencies during provisioning for reliable Infrastructure as Code.

In this lesson, we’ll explore how OpenTofu records resource attributes and manages dependencies during provisioning. Understanding these concepts is key to writing reliable Infrastructure as Code.

## Exported Attributes

When you define a resource in OpenTofu, several attributes are exported after creation. For example, create an AWS key pair:

```hcl theme={null}
resource "aws_key_pair" "alpha" {
  key_name   = "alpha"
  public_key = "ssh-rsa AAAAB3NzaC1yc2EAAAAADAQABAAABAQD3.....alpha@a-server"
}
```

Here, `public_key` is a required argument. After running `tofu apply`, inspect the exported values using:

```bash theme={null}
tofu show
```

Example output:

```bash theme={null}
# aws_key_pair.alpha:
resource "aws_key_pair" "alpha" {
  arn         = "arn:aws:ec2:us-east-1:key-pair/alpha"
  fingerprint = "d7:ff:a6:63:18:64:9c:57:a1:ee:ca:a4:ad:c2:81:62"
  id          = "alpha"
  key_name    = "alpha"
  public_key  = "ssh-rsa AAAAB3NzaC1yc2EAAAAADAQABAAABAQD3F6ty... alpha@a-server"
  tags_all    = {}
}
```

| Attribute   | Description                                      |
| ----------- | ------------------------------------------------ |
| arn         | Amazon Resource Name for the key pair            |
| fingerprint | SHA1 fingerprint of the public key               |
| id          | Unique identifier (same as `key_name`)           |
| key\_name   | Name assigned to the key pair                    |
| public\_key | SSH public key supplied by the user              |
| tags\_all   | Combined map of resource and provider-level tags |

<Callout icon="lightbulb" color="#1CB2FE">
  You can target a specific resource by running `tofu show aws_key_pair.alpha`.\
  Learn more in the \[OpenTofu CLI Docs].
</Callout>

## Referencing Exported Attributes

Exported attributes become inputs for other resources. For instance, associate the key pair with an EC2 instance:

```hcl theme={null}
resource "aws_instance" "cerberus" {
  ami           = var.ami
  instance_type = var.instance_type
  key_name      = aws_key_pair.alpha.key_name
}
```

The reference `aws_key_pair.alpha.key_name` follows the format:

```text theme={null}
resource_type.resource_name.attribute
```

This creates an **implicit dependency**, ensuring `aws_key_pair.alpha` is created before `aws_instance.cerberus`.

## Implicit Dependencies in Action

When you run `tofu apply`, OpenTofu will build the dependency graph and provision resources in the correct order:

```bash theme={null}
$ tofu apply
aws_key_pair.alpha: Creating...
aws_key_pair.alpha: Creation complete after 1s [id=alpha]
aws_instance.cerberus: Creating...
aws_instance.cerberus: Creation complete after 10s [id=i-c791dc46a6639d4a7]
Apply complete! Resources: 2 added, 0 changed, 0 destroyed
```

During `tofu destroy`, the reverse order is applied: the EC2 instance is terminated before the key pair.

<Callout icon="lightbulb" color="#1CB2FE">
  Implicit dependencies eliminate race conditions and ensure resources are created or destroyed in the correct sequence.\
  Read more about the \[AWS Provider] for detailed attribute information.
</Callout>

## Explicit Dependencies with `depends_on`

If resources lack direct attribute references but still require ordering, use the `depends_on` meta-argument:

```hcl theme={null}
resource "aws_instance" "db" {
  ami           = var.db_ami
  instance_type = var.db_instance_type
}

resource "aws_instance" "web" {
  ami           = var.web_ami
  instance_type = var.web_instance_type

  depends_on = [
    aws_instance.db
  ]
}
```

Here, `aws_instance.web` will wait for `aws_instance.db` to finish creation first.

<Callout icon="triangle-alert" color="#FF6B6B">
  Overusing `depends_on` can complicate your configuration. Prefer implicit references whenever possible.\
  For advanced dependency control, see the \[Infrastructure as Code] best practices.
</Callout>

***

That’s it for this lesson on resource attributes and dependencies in OpenTofu. In the next module, we’ll cover **outputs** and **remote backends** to share state across your team.

## Links and References

* [OpenTofu CLI Docs](https://docs.opentofu.io/cli)
* [AWS Provider](https://registry.terraform.io/providers/hashicorp/aws/latest/docs)
* [Infrastructure as Code](https://en.wikipedia.org/wiki/Infrastructure_as_code)

<CardGroup>
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