Meta-arguments overview in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are meta-arguments in Terraform?

Meta-arguments are special arguments that can be used inside Terraform resource blocks to control how resources behave, like loops, conditions, or dependencies.

beginner

Name three common meta-arguments in Terraform.

Common meta-arguments include count (to create multiple instances), for_each (to create resources from a map or set), and depends_on (to specify resource dependencies).

beginner

How does the count meta-argument work?

The count meta-argument tells Terraform how many copies of a resource to create. For example, count = 3 creates three identical resources.

intermediate

What is the purpose of depends_on in Terraform?

depends_on tells Terraform to create or update a resource only after certain other resources are done. It helps control the order of operations.

intermediate

When should you use for_each instead of count?

Use for_each when you want to create resources based on a map or set with unique keys, so you can easily reference each resource by its key. count is simpler but only uses numeric indexes.

Which meta-argument creates multiple copies of a resource by number?

A for_each

B count

C depends_on

D lifecycle

count creates multiple copies by number. for_each uses keys, depends_on manages dependencies, and lifecycle controls resource lifecycle.

What does depends_on control in Terraform?

A Resource creation order

B Number of resource copies

C Resource naming

D Resource tags

depends_on controls the order in which Terraform creates or updates resources.

Which meta-argument allows creating resources from a map or set with unique keys?

A count

B depends_on

C provider

D for_each

for_each creates resources from a map or set using unique keys.

Can you use both count and for_each in the same resource block?

A Only if the resource supports it

B Yes, always

C No, they cannot be used together

D Only with depends_on

You cannot use count and for_each together in the same resource block.

What happens if you set count = 0 for a resource?

A Terraform creates zero resources

B Terraform creates default resources

C Terraform throws an error

D Terraform creates one resource

Setting count = 0 means Terraform creates no instances of that resource.

Explain what meta-arguments are in Terraform and give examples.

Think about special settings inside resource blocks that change how many or when resources are created.

Describe the difference between using count and for_each meta-arguments.

Consider how you choose which resources to create and how you refer to them.

Practice

1. Which meta-argument in Terraform allows you to create multiple instances of a resource easily using an integer?

easy

A. count

B. depends_on

C. lifecycle

D. for_each

Solution

1. Step 1: Understand the purpose of count

   The count meta-argument lets you specify how many copies of a resource to create.

2. Step 2: Compare with other meta-arguments

   depends_on manages dependencies, lifecycle controls resource behavior, and for_each creates multiple instances but with keys, not just count.

3. Final Answer:

   count -> Option A

4. Quick Check:

   Multiple instances = count [OK]

Hint: Use count to repeat resources by number [OK]

Common Mistakes:

• Confusing count with depends_on
• Thinking lifecycle creates multiple resources
• Mixing count and for_each without understanding difference

2. Which of the following is the correct syntax to use the depends_on meta-argument in a resource block?

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.id]

Solution

1. Step 1: Recall depends_on syntax

   depends_on expects a list of resource references without quotes.

2. Step 2: Analyze options

   depends_on = [aws_instance.example] uses a list with resource reference correctly. depends_on = aws_instance.example misses list brackets. depends_on = ["aws_instance.example"] uses quotes making it a string, not a reference. depends_on = [aws_instance.example.id] uses an attribute which is invalid here.

3. Final Answer:

   depends_on = [aws_instance.example] -> Option C

4. Quick Check:

   List of resource references = depends_on = [aws_instance.example] [OK]

Hint: Always use square brackets with resource references for depends_on [OK]

Common Mistakes:

• Omitting brackets for depends_on list
• Using quotes around resource names
• Referencing resource attributes instead of resource itself

3. Given the following Terraform snippet:

resource "aws_instance" "example" {
  count = 3
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

What will be the number of instances created and their resource addresses?

medium

A. 1 instance: aws_instance.example

B. 3 instances: aws_instance.example[0], aws_instance.example[1], aws_instance.example[2]

C. 3 instances: aws_instance.example.0, aws_instance.example.1, aws_instance.example.2

D. Error due to missing for_each

Solution

1. Step 1: Understand count behavior

   count = 3 creates three instances indexed from 0 to 2.

2. Step 2: Identify resource addresses format

   Terraform uses square brackets for indexed resources, so addresses are aws_instance.example[0], aws_instance.example[1], and aws_instance.example[2].

3. Final Answer:

   3 instances: aws_instance.example[0], aws_instance.example[1], aws_instance.example[2] -> Option B

4. Quick Check:

   Count creates indexed instances [OK]

Hint: Count creates indexed resources with square brackets [OK]

Common Mistakes:

• Thinking only one instance is created
• Using dot notation instead of brackets for indexes
• Confusing count with for_each syntax

4. You wrote this Terraform resource:

resource "aws_s3_bucket" "example" {
  for_each = ["a", "b"]
  bucket = each.value
}

What is the error in this configuration?

medium

A. Missing count argument

B. each.value is invalid inside resource blocks

C. bucket attribute cannot use each.value

D. for_each must be a map or set, not a list

Solution

1. Step 1: Check for_each type requirements

   for_each requires a map or set of strings, not a list.

2. Step 2: Analyze provided value

   The value is a list ["a", "b"], which is invalid for for_each. It should be a set or map.

3. Final Answer:

   for_each must be a map or set, not a list -> Option D

4. Quick Check:

   for_each needs map/set, not list [OK]

Hint: Use map or set for for_each, not list [OK]

Common Mistakes:

• Using list instead of set/map for for_each
• Misunderstanding each.value usage
• Confusing count and for_each requirements

5. You want to create multiple AWS EC2 instances with different names and ensure one instance is always created before the others. Which meta-arguments combination should you use?

hard

A. Use for_each with a map of names and depends_on to order creation

B. Use count with a number and lifecycle to order creation

C. Use depends_on only, no count or for_each

D. Use lifecycle with create_before_destroy only

Solution

1. Step 1: Choose meta-argument for multiple named instances

   for_each with a map lets you create instances with specific names as keys.

2. Step 2: Ensure creation order

   depends_on lets you specify that one resource must be created before others.

3. Final Answer:

   Use for_each with a map of names and depends_on to order creation -> Option A

4. Quick Check:

   Multiple named + order = for_each + depends_on [OK]

Hint: Combine for_each and depends_on for named ordered resources [OK]

Common Mistakes:

• Using count without names for multiple instances
• Relying on lifecycle for creation order
• Ignoring depends_on for resource dependencies