Depends_on for explicit dependencies in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of depends_on in Terraform?

depends_on explicitly tells Terraform that one resource must be created or updated before another. It controls the order of operations to avoid errors.

beginner

How does Terraform normally determine resource creation order without depends_on?

Terraform uses implicit dependencies by analyzing references between resources, like when one resource uses an output or attribute of another.

intermediate

When should you use depends_on in your Terraform configuration?

Use depends_on when Terraform cannot detect a dependency automatically but you know one resource must be created before another, such as with external resources or side effects.

intermediate

What happens if you omit depends_on when an explicit dependency is needed?

Terraform may try to create or update resources in the wrong order, causing errors or failures during deployment.

beginner

Example: How to use depends_on to make resource B wait for resource A?

resource "aws_instance" "A" {
  # config
}

resource "aws_instance" "B" {
  # config
  depends_on = [aws_instance.A]
}

What does depends_on do in Terraform?

A Changes resource configuration

B Specifies explicit resource creation order

C Deletes resources automatically

D Creates new resource types

depends_on explicitly sets the order Terraform creates or updates resources.

How does Terraform find dependencies without depends_on?

A By user input only

B By random order

C By analyzing resource references

D It does not find dependencies

Terraform detects implicit dependencies by checking if one resource uses another's outputs or attributes.

When is depends_on necessary?

A When Terraform cannot detect a dependency automatically

B Always, for every resource

C Only for deleting resources

D Never, it is deprecated

Use depends_on when implicit detection is not enough to ensure correct order.

What is a risk of missing a needed depends_on?

A Terraform will crash immediately

B Terraform will ignore the resource

C Resources will be duplicated

D Resources may be created in wrong order causing errors

Without explicit dependency, Terraform might create resources too early or late, causing failures.

Which syntax correctly uses depends_on?

A depends_on = [aws_instance.A]

B depends_on = aws_instance.A

C depends_on: aws_instance.A

D depends_on => aws_instance.A

depends_on expects a list of resources, so square brackets are required.

Explain in your own words why and how you would use depends_on in Terraform.

Think about cases where Terraform might not know which resource to create first.

Describe what could happen if you forget to add depends_on when it is needed.

Consider the impact on your infrastructure deployment process.