Depends_on for explicit dependencies in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the purpose of depends_on in Terraform

What is the main purpose of using depends_on in a Terraform resource configuration?

A To create a resource only if another resource exists in the cloud provider

B To explicitly specify resource creation order when Terraform cannot infer it automatically

C To define variables that are used inside resource blocks

D To automatically delete dependent resources when a resource is destroyed

💡 Hint

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

depends_on tells Terraform explicitly which resources must be created or destroyed before others, ensuring correct order when implicit dependencies are not detected.

❓ Configuration

intermediate

Identifying the effect of depends_on in resource creation

Given the following Terraform snippet, what will be the order of resource creation?

resource "aws_instance" "web" {
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

resource "aws_eip" "ip" {
  instance = aws_instance.web.id
  depends_on = [aws_instance.web]
}

A Terraform will throw an error due to circular dependency

B The <code>aws_eip.ip</code> is created first, then <code>aws_instance.web</code>

C Both resources are created simultaneously

D The <code>aws_instance.web</code> is created first, then <code>aws_eip.ip</code>

💡 Hint

Look at the depends_on and the implicit reference inside aws_eip.

The aws_eip.ip resource depends explicitly on aws_instance.web, so Terraform creates the instance first, then the Elastic IP.

❓ Architecture

advanced

Using depends_on to manage complex resource dependencies

You have three resources: db, app, and monitoring. The app must be created after db, and monitoring must be created after both db and app. Which depends_on configuration correctly enforces this?

A <code>app depends_on = [db]</code> and <code>monitoring depends_on = [db, app]</code>

B <code>app depends_on = [monitoring]</code> and <code>monitoring depends_on = [db]</code>

C <code>db depends_on = [app]</code> and <code>monitoring depends_on = [app]</code>

D <code>monitoring depends_on = [db]</code> only

💡 Hint

Think about the order: db → app → monitoring.

Setting app depends_on = [db] ensures app waits for db. Setting monitoring depends_on = [db, app] ensures monitoring waits for both.

❓ security

advanced

Impact of missing depends_on on security group rules

You have a security group resource and an instance resource. The instance uses the security group ID. If you forget to add depends_on for the instance on the security group, what could happen?

A Terraform might try to create the instance before the security group, causing a failure

B Terraform will automatically detect the dependency and create resources in correct order

C The security group will be deleted before the instance is created

D Terraform will ignore the security group and create the instance without it

💡 Hint

Consider if Terraform can always detect dependencies from resource attributes.

If the instance references the security group ID directly, Terraform usually detects the dependency. But if the reference is indirect or missing, missing depends_on can cause creation order issues and failures.

❓ service_behavior

expert

Effect of depends_on on resource destruction order

Consider two Terraform resources: resource "aws_lb" "load_balancer" and resource "aws_lb_target_group" "target_group". The load balancer depends on the target group using depends_on. When destroying the infrastructure, what is the destruction order?

A The load balancer is destroyed first, then the target group

B Terraform will fail to destroy due to dependency conflict

C The target group is destroyed first, then the load balancer

D Both are destroyed simultaneously

💡 Hint

Think about how depends_on affects destruction order compared to creation order.

depends_on ensures the load balancer is created after the target group, so during destruction, Terraform destroys the load balancer first, then the target group.