Depends_on for explicit dependencies in Terraform - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an explicit dependency on the resource 'aws_vpc.main'.

Terraform

resource "aws_subnet" "example" {
  vpc_id = aws_vpc.main.id
  cidr_block = "10.0.1.0/24"
  [1] = [aws_vpc.main]
}

Drag options to blanks, or click blank then click option'

Aprovider

Bdepends_on

Clifecycle

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'provider' instead of 'depends_on'.

Forgetting to wrap the resource in a list.

The depends_on argument explicitly declares a dependency on another resource, ensuring Terraform creates the dependent resource first.

2fill in blank

medium

Complete the code to explicitly depend on both 'aws_vpc.main' and 'aws_internet_gateway.gw'.

Terraform

resource "aws_route_table" "rt" {
  vpc_id = aws_vpc.main.id
  [1] = [aws_vpc.main, aws_internet_gateway.gw]
}

Drag options to blanks, or click blank then click option'

Acount

Bprovider

Cdepends_on

Dlifecycle

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'count' or 'provider' instead of 'depends_on'.

Not using a list for multiple dependencies.

The depends_on argument can list multiple resources to ensure they are created before this resource.

3fill in blank

hard

Fix the error in the code by correctly specifying the explicit dependency on 'aws_security_group.sg'.

Terraform

resource "aws_instance" "web" {
  ami           = "ami-123456"
  instance_type = "t2.micro"
  [1] = [aws_security_group.sg]
}

Drag options to blanks, or click blank then click option'

Adepends_on

Bdepends

Cdependency

DdependsOn

Attempts:

3 left

💡 Hint

Common Mistakes

Using camelCase or incorrect spellings like 'dependsOn' or 'dependency'.

Omitting the list brackets around the resource.

The correct meta-argument is depends_on. Other variants are invalid and cause errors.

4fill in blank

hard

Fill both blanks to explicitly depend on 'aws_lb.main' and 'aws_lb_target_group.main'.

Terraform

resource "aws_lb_listener" "front_end" {
  load_balancer_arn = aws_lb.main.arn
  port              = 80
  protocol          = "HTTP"
  [1] = [aws_lb.main, [2]]
}

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Adepends_on

Baws_lb_target_group.main

Dprovider

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'provider' instead of 'depends_on'.

Not including both resources in the list.

The depends_on argument is used to declare explicit dependencies. The list includes both resources.

5fill in blank

hard

Fill all three blanks to explicitly depend on 'aws_db_instance.main' and 'aws_security_group.db_sg'.

Terraform

resource "aws_db_parameter_group" "db_pg" {
  name        = "my-db-pg"
  family      = "mysql5.7"
  description = "Custom parameter group"
  [1] = [[2], [3]]
}

Drag options to blanks, or click blank then click option'

Adepends_on

Baws_db_instance.main

Caws_security_group.db_sg

Daws_subnet.db_subnet

Attempts:

3 left

💡 Hint

Common Mistakes

Not using a list for multiple dependencies.

Including resources not needed for this dependency.

The depends_on argument lists resources to explicitly depend on. Here, it includes the DB instance and security group. The subnet is not included in this example.

Practice

1. What is the main purpose of depends_on in Terraform?

easy

A. To delete resources automatically

B. To define the resource type

C. To set resource properties

D. To explicitly specify the order in which resources are created

Solution

1. Step 1: Understand resource creation order

   Terraform creates resources in parallel by default, but sometimes one resource must be created before another.

2. Step 2: Role of depends_on

   The depends_on attribute explicitly tells Terraform to wait for one resource before creating another.

3. Final Answer:

   To explicitly specify the order in which resources are created -> Option D

4. Quick Check:

   depends_on controls creation order = A [OK]

Hint: depends_on sets creation order explicitly [OK]

Common Mistakes:

• Confusing depends_on with resource type definition
• Thinking depends_on sets resource properties
• Assuming depends_on deletes resources

2. Which of the following is the correct syntax to add depends_on for a resource named aws_instance.example?

easy

A. depends_on = aws_instance.example

B. depends_on = {aws_instance.example}

C. depends_on = [aws_instance.example]

D. depends_on = ["aws_instance.example"]

Solution

1. Step 1: Understand depends_on syntax

   The depends_on attribute expects a list of resource references.

2. Step 2: Correct list format

   Resources must be inside square brackets as unquoted references, like [aws_instance.example].

3. Final Answer:

   depends_on = [aws_instance.example] -> Option C

4. Quick Check:

   depends_on requires list of resource references = B [OK]

Hint: Use list of unquoted resource references for depends_on [OK]

Common Mistakes:

• Omitting square brackets around resource reference
• Using curly braces instead of square brackets
• Not using a list format

3. Given the following Terraform snippet, what will happen during apply?

resource "aws_s3_bucket" "bucket" {
  bucket = "my-bucket"
}

resource "aws_s3_bucket_policy" "policy" {
  bucket = aws_s3_bucket.bucket.id
  policy = "..."
  depends_on = [aws_s3_bucket.bucket]
}

medium

A. The bucket will be created before the bucket policy

B. The bucket policy will be created before the bucket

C. Both resources will be created simultaneously

D. Terraform will throw a syntax error

Solution

1. Step 1: Analyze depends_on usage

   The bucket policy resource explicitly depends on the bucket resource using depends_on, so the bucket must exist first.

2. Step 2: Understand creation order

   Terraform will create the bucket first, then the bucket policy, ensuring the policy applies to an existing bucket.

3. Final Answer:

   The bucket will be created before the bucket policy -> Option A

4. Quick Check:

   depends_on enforces bucket before policy = B [OK]

Hint: depends_on enforces creation order, bucket before policy [OK]

Common Mistakes:

• Assuming simultaneous creation despite depends_on
• Thinking depends_on reverses order
• Confusing resource references with strings

4. You wrote this Terraform code but get an error:

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
}

What is the problem?

medium

A. depends_on should be a list of resource references

B. instance attribute is incorrect

C. Resource names cannot be used in depends_on

D. The AMI ID is invalid

Solution

1. Step 1: Check depends_on syntax

   The depends_on attribute must be a list, even if it has one resource.

2. Step 2: Identify error in code

   Here, depends_on = aws_instance.web is missing square brackets, causing a syntax error.

3. Final Answer:

   depends_on should be a list of resource references -> Option A

4. Quick Check:

   depends_on needs list syntax = A [OK]

Hint: Always use square brackets for depends_on list [OK]

Common Mistakes:

• Using single resource without list brackets
• Confusing depends_on with resource attributes
• Ignoring Terraform syntax requirements

5. You have two resources: aws_db_instance.db and aws_ecs_service.ecs. The ECS service must start only after the database is fully created. How should you configure depends_on in aws_ecs_service.ecs to ensure this?

hard

A. depends_on = aws_db_instance.db

B. depends_on = [aws_db_instance.db]

C. depends_on = ["aws_db_instance.db"]

D. depends_on = {"aws_db_instance.db"}

Solution

1. Step 1: Understand depends_on format

   Terraform requires depends_on to be a list of resource references.

2. Step 2: Correct usage for ECS service

   To make ECS depend on the DB, use depends_on = [aws_db_instance.db] inside the ECS resource block.

3. Final Answer:

   depends_on = [aws_db_instance.db] -> Option B

4. Quick Check:

   depends_on list of resource references for explicit dependency = A [OK]

Hint: Use list of unquoted resource references for depends_on [OK]

Common Mistakes:

• Omitting square brackets around resource reference
• Omitting square brackets
• Using curly braces instead of brackets