For expressions for transformation in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding For Expressions Output

Given the Terraform expression [for i in [1, 2, 3] : i * 2], what is the resulting list?

Terraform

[for i in [1, 2, 3] : i * 2]

A [2, 4, 6]

B [1, 2, 3]

C [1, 4, 9]

D [3, 6, 9]

💡 Hint

Each element is multiplied by 2.

The for expression iterates over each element and multiplies it by 2, producing [2, 4, 6].

❓ Configuration

intermediate

Filtering with For Expressions

What is the output of this Terraform expression?
[for n in [1, 2, 3, 4] : n if n % 2 == 0]

Terraform

[for n in [1, 2, 3, 4] : n if n % 2 == 0]

A [1, 3]

B [2, 4]

C [1, 2, 3, 4]

D SyntaxError

💡 Hint

Only even numbers are included.

The for expression filters to include only numbers divisible by 2, resulting in [2, 4].

❓ Architecture

advanced

Transforming Map Values with For Expressions

Given this Terraform map:
{"a" = 1, "b" = 2, "c" = 3}
What is the output of this expression?
{for k, v in {"a" = 1, "b" = 2, "c" = 3} : k => v * v}

Terraform

{for k, v in {"a" = 1, "b" = 2, "c" = 3} : k => v * v}

A [1, 4, 9]

B {"a" = 2, "b" = 3, "c" = 4}

C {"a" = 1, "b" = 4, "c" = 9}

D SyntaxError

💡 Hint

Each value is squared, keys remain the same.

The for expression creates a new map with the same keys but squares each value.

❓ service_behavior

advanced

For Expressions with Nested Lists

What is the output of this Terraform expression?
[for sublist in [[1, 2], [3, 4]] : [for n in sublist : n * 10]]

Terraform

[for sublist in [[1, 2], [3, 4]] : [for n in sublist : n * 10]]

A [[10, 20], [30, 40]]

B [10, 20, 30, 40]

C [[1, 2], [3, 4]]

D TypeError

💡 Hint

Each inner list element is multiplied by 10.

The outer for expression iterates over sublists, and the inner one multiplies each number by 10, preserving the nested list structure.

❓ security

expert

For Expressions and Sensitive Data Handling

Consider a Terraform variable var.passwords = ["pass1", "pass2"] marked as sensitive. Which for expression correctly creates a new list masking each password with asterisks of the same length, without exposing the original passwords in logs or state?

A [for p in var.passwords : substr(p, 0, 2)]

B [for p in var.passwords : p]

C [for p in var.passwords : "*****"]

D [for p in var.passwords : "*" * length(p)]

💡 Hint

Mask length should match original password length without revealing content.

Option D creates a masked string of asterisks matching the length of each password, avoiding exposure of actual passwords. Option D exposes passwords directly. Option D uses fixed length masking which may reveal length info incorrectly. Option D exposes part of the password.

Practice

1. What does a for expression in Terraform primarily do?

easy

A. Creates a new resource in the cloud

B. Transforms each item in a list or map into a new list or map

C. Deletes resources based on a condition

D. Runs a shell command on the local machine

Solution

1. Step 1: Understand the purpose of for expressions

   For expressions in Terraform are used to transform collections like lists or maps into new collections by applying a transformation to each item.

2. Step 2: Differentiate from other Terraform actions

   Creating or deleting resources and running shell commands are not done by for expressions; they are handled by resource blocks or provisioners.

3. Final Answer:

   Transforms each item in a list or map into a new list or map -> Option B

4. Quick Check:

   For expressions = transform collections [OK]

Hint: For expressions change each item in a list/map to a new form [OK]

Common Mistakes:

• Thinking for expressions create or delete resources
• Confusing for expressions with provisioners
• Assuming for expressions run commands

2. Which of the following is the correct syntax for a simple for expression transforming a list [1, 2, 3] to their squares in Terraform?

easy

A. [for n in [1, 2, 3] : n * n]

B. [for n : n * n in [1, 2, 3]]

C. [for n in [1, 2, 3] n * n]

D. [for n in [1, 2, 3] => n * n]

Solution

1. Step 1: Recall Terraform for expression syntax

   The correct syntax is: [for <variable> in <list> : <expression>]. [for n in [1, 2, 3] : n * n] matches this exactly.

2. Step 2: Check other options for syntax errors

   [for n : n * n in [1, 2, 3]] has wrong order, [for n in [1, 2, 3] n * n] misses colon, [for n in [1, 2, 3] => n * n] uses => which is invalid in Terraform for expressions.

3. Final Answer:

   [for n in [1, 2, 3] : n * n] -> Option A

4. Quick Check:

   Correct syntax = [for var in list : expr] [OK]

Hint: Remember syntax: for var in list : expression [OK]

Common Mistakes:

• Omitting the colon ':' after the list variable
• Using arrow '=>' instead of colon
• Placing expression before 'in' keyword

3. Given the Terraform expression:

[for s in ["apple", "banana", "cherry"] : upper(s) if length(s) > 5]

What is the resulting list?

medium

A. ["banana", "cherry"]

B. ["APPLE", "BANANA", "CHERRY"]

C. ["BANANA", "CHERRY"]

D. ["APPLE"]

Solution

1. Step 1: Identify filtering condition

   The expression filters strings with length greater than 5. "banana" (6) and "cherry" (6) qualify; "apple" (5) does not.

2. Step 2: Apply transformation function

   For qualifying strings, upper(s) converts them to uppercase: "BANANA", "CHERRY".

3. Final Answer:

   ["BANANA", "CHERRY"] -> Option C

4. Quick Check:

   Filter length > 5 + uppercase = ["BANANA", "CHERRY"] [OK]

Hint: Filter first, then transform inside for expression [OK]

Common Mistakes:

• Including items that don't meet the if condition
• Not applying the upper() function
• Confusing syntax order of filter and expression

4. Identify the error in this Terraform for expression:

[for k, v in {a=1, b=2} : "${k}=${v}" if v > 1]

medium

A. Using if condition outside the for expression

B. Missing colon after the map

C. Incorrect use of string interpolation syntax

D. Using two variables without parentheses in for expression

Solution

1. Step 1: Check syntax for multiple variables in for expressions

   When using two variables (key and value) in a for expression, parentheses are required: for (k, v) in map.

2. Step 2: Identify the error in given expression

   The expression uses 'for k, v in' without parentheses, causing syntax error.

3. Final Answer:

   Using two variables without parentheses in for expression -> Option D

4. Quick Check:

   Two variables need parentheses: for (k, v) in map [OK]

Hint: Use parentheses for multiple variables in for expressions [OK]

Common Mistakes:

• Omitting parentheses around multiple variables
• Placing if condition incorrectly
• Misusing string interpolation syntax

5. You have a map of instance names to their CPU counts:

{"web"=2, "db"=4, "cache"=1}

Write a Terraform for expression that creates a list of instance names with CPU count greater than 1, all in uppercase.

hard

A. [for (name, cpu) in {"web"=2, "db"=4, "cache"=1} : upper(name) if cpu > 1]

B. [for name, cpu in {"web"=2, "db"=4, "cache"=1} : upper(name) if cpu > 1]

C. [for (name, cpu) in {"web"=2, "db"=4, "cache"=1} : name if cpu > 1]

D. [for (name, cpu) in {"web"=2, "db"=4, "cache"=1} : upper(cpu) if cpu > 1]

Solution

1. Step 1: Use parentheses for key-value iteration

   When iterating over a map with two variables, use parentheses: for (name, cpu) in map.

2. Step 2: Apply filter and transformation

   Filter with if cpu > 1 to select "web" and "db". Transform name to uppercase with upper(name).

3. Final Answer:

   [for (name, cpu) in {"web"=2, "db"=4, "cache"=1} : upper(name) if cpu > 1] -> Option A

4. Quick Check:

   Parentheses + filter + upper(name) = [for (name, cpu) in {"web"=2, "db"=4, "cache"=1} : upper(name) if cpu > 1] [OK]

Hint: Parentheses for map keys, filter with if, transform with upper() [OK]

Common Mistakes:

• Omitting parentheses for key-value pairs
• Transforming cpu instead of name
• Not filtering correctly with if condition