Panchanan Panigrahi

Posted on Sep 28

27 Powerful Built-in Terraform Functions to Enhance Your Workflow

#devops #terraform #cloud #beginners

What are Terraform Functions?
1. toset Function
2. format Function
3. formatlist Function
4. join Function
5. split Function
6. length Function
7. lookup Function
8. merge Function
9. concat Function
10. flatten Function
11. slice Function
12. zipmap Function
13. Working with key and value in Maps
14. element Function
15. index Function
16. contains Function
17. distinct Function
18. coalesce Function
19. coalescelist Function
20. one Function
21. try Function
22. can Function
23. file Function
24. templatefile Function
25. Base64 Functions: base64encode and base64decode
26. JSON Functions: jsonencode and jsondecode
27. YAML Functions: yamlencode and yamldecode
Final Thoughts

Terraform is a powerful Infrastructure as Code (IaC) tool packed with built-in functions that enhance your workflow. These functions are game-changers for managing and automating infrastructure.

In this blog, we’ll explore 27 essential built-in functions every Terraform user should know. Whether you're a beginner or looking to refine your skills, this guide will help you write efficient, maintainable, and scalable code. Let’s discover how these functions can elevate your Terraform journey!

What are Terraform Functions?

Terraform functions are versatile tools for data manipulation and transformation in your configurations. They allow for operations like string formatting, arithmetic calculations, and managing lists and maps.

By using these functions, you can create dynamic and maintainable infrastructure code that adheres to the DRY (Don’t Repeat Yourself) principle, simplifying the provisioning and management of your resources.

1. toset Function

The toset function is used to convert a list or tuple into a set. This transformation helps eliminate duplicate values, ensuring that each element in the set is unique.

Syntax:

toset(list)

Example:

variable "my_list" {
  default = ["apple", "banana", "apple", "orange"]
}

output "unique_fruits" {
  value = toset(var.my_list)
}

In this example, the toset function converts the list ["apple", "banana", "apple", "orange"] into a set, resulting in {"apple", "banana", "orange"} by removing the duplicate "apple." This is particularly useful when you want to ensure unique values in your configurations.

2. format Function

The format function allows you to create a formatted string by embedding variable values into a predefined format string. It offers flexibility in handling various data types like strings, integers, and floats, making it a versatile tool for generating dynamic content.

Syntax:

format(format_string, arg1, arg2, ...)

format_string: The main string containing placeholders (e.g., %s, %d, %.2f) that specify how the variable values should be formatted.
arg1, arg2, ...: Values to be substituted in the placeholders.

Supported Placeholders:

%s – For strings
%d – For integers
%f – For floating-point numbers
%t – For boolean values
%v – For automatic formatting (default representation of the value)
%#v – For a Go-syntax representation of the value (useful for complex data structures)

Examples:

1. Formatting Strings

variable "first_name" {
  default = "John"
}

variable "last_name" {
  default = "Doe"
}

output "formatted_name" {
  value = format("Full Name: %s %s", var.first_name, var.last_name)
}

Output: "Full Name: John Doe"

2. Formatting Integers

variable "age" {
  default = 30
}

output "formatted_age" {
  value = format("Age: %d years", var.age)
}

Output: "Age: 30 years"

3. Formatting Floats

variable "price" {
  default = 25.6789
}

output "formatted_price" {
  value = format("Total Price: %.2f USD", var.price)
}

Output: "Total Price: 25.68 USD"

%.2f specifies that the float should be formatted with 2 decimal places.

4. Boolean Values

variable "is_active" {
  default = true
}

output "status_message" {
  value = format("Status: %t", var.is_active)
}

Output: "Status: true"

5. Using Automatic Formatting with `%v`

variable "items" {
  default = [1, "apple", 3.14, true]
}

output "mixed_output" {
  value = format("Values: %v", var.items)
}

Output: "Values: [1 apple 3.14 true]"

3. formatlist Function

The formatlist function formats a list of values using a specified pattern. It’s perfect for situations where you need to apply consistent formatting to multiple elements.

Syntax:

formatlist(format_string, values...)

format_string: The format pattern to apply to each value in the list.
values...: The list of values to format.

Supported Placeholders:

The placeholders in formatlist work the same way as those in the format function, allowing you to handle strings, integers, floats, and booleans.

Examples:

1. Formatting a List of Strings

variable "cities" {
  default = ["New York", "Los Angeles", "Chicago"]
}

output "city_greetings" {
  value = formatlist("Welcome to %s!", var.cities)
}

Output: ["Welcome to New York!", "Welcome to Los Angeles!", "Welcome to Chicago!"]

2. Formatting a List of Integers

variable "scores" {
  default = [95, 85, 75]
}

output "formatted_scores" {
  value = formatlist("Score: %d", var.scores)
}

Output: ["Score: 95", "Score: 85", "Score: 75"]

3. Formatting a List of Floats

variable "percentages" {
  default = [0.875, 0.923, 0.658]
}

output "formatted_percentages" {
  value = formatlist("Percentage: %.1f%%", var.percentages)
}

Output: ["Percentage: 87.5%", "Percentage: 92.3%", "Percentage: 65.8%"]

The %.1f%% format specifies one decimal place and includes the percentage symbol.

4. Using Automatic Formatting with `%v` in Lists

variable "mixed_values" {
  default = [42, "banana", true]
}

output "formatted_list" {
  value = formatlist("Value: %v", var.mixed_values)
}

Output: ["Value: 42", "Value: banana", "Value: true"]

4. join Function

The join function in Terraform is used to concatenate elements of a list into a single string, using a specified delimiter. This is especially useful when you need to combine multiple values into a single formatted string.

Syntax:

join(delimiter, list)

delimiter: The string that separates each element in the list when joined.
list: The list of values to be concatenated into a single string.

Examples:

1. Joining a List of Strings

variable "languages" {
  default = ["Go", "Python", "Java"]
}

output "joined_languages" {
  value = join(", ", var.languages)
}

Output: "Go, Python, Java"

The join function combines the list into a single string, using ", " as the separator.

2. Joining with No Delimiter

variable "letters" {
  default = ["a", "b", "c"]
}

output "combined_letters" {
  value = join("", var.letters)
}

Output: "abc"

The join function combines all elements with no space between them.

3. Joining Integers (Converted to Strings)

Although join directly works with strings, you can convert integers to strings before joining them:

variable "numbers" {
  default = ["1", "2", "3"]
}

output "joined_numbers" {
  value = join("-", var.numbers)
}

Output: "1-2-3"

This example demonstrates that if numbers are already strings, you can join them seamlessly using "-" as a delimiter.

5. split Function

The split function does the opposite of join. It splits a string into a list of substrings based on a specified delimiter, making it useful when you need to break down complex strings into individual components.

Syntax:

split(delimiter, string)

delimiter: The string used to split the main string.
string: The original string to be split into a list.

Examples:

1. Splitting a Comma-Separated String

variable "comma_separated" {
  default = "apple,orange,banana"
}

output "fruits_list" {
  value = split(",", var.comma_separated)
}

Output: ["apple", "orange", "banana"]

The split function converts the comma-separated string into a list of fruits.

2. Splitting a String with Spaces

variable "sentence" {
  default = "Terraform makes infrastructure simple"
}

output "words_list" {
  value = split(" ", var.sentence)
}

Output: ["Terraform", "makes", "infrastructure", "simple"]

Here, the split function breaks the sentence into individual words using a space as the delimiter.

3. Splitting with a Complex Delimiter

variable "complex_string" {
  default = "one#two#three#four"
}

output "split_result" {
  value = split("#", var.complex_string)
}

Output: ["one", "two", "three", "four"]

The split function uses "#" to separate the elements.

4. Splitting a String and Joining Again

You can combine split and join for more complex manipulations:

variable "data" {
  default = "cat,dog,bird"
}

output "modified_animals" {
  value = join(" | ", split(",", var.data))
}

Output: "cat | dog | bird"

This example demonstrates splitting a comma-separated string into a list, then joining it back with " | " as the new delimiter.

6. length Function

The length function is used to determine the number of elements in a collection, such as a list, map, or string. It's quite handy for validation, conditionals, or loops within your Terraform configurations.

Syntax:

length(collection)

collection: Can be a list, map, or string.

Examples:

1. Finding the Length of a List

variable "colors" {
  default = ["red", "green", "blue"]
}

output "colors_count" {
  value = length(var.colors)
}

Output: 3

The length function counts the number of elements in the list colors.

2. Determining the Length of a Map

variable "person" {
  default = {
    name   = "Alice"
    age    = 30
    gender = "female"
  }
}

output "person_attributes" {
  value = length(var.person)
}

Output: 3

The length function counts the number of key-value pairs in the map person.

3. Calculating the Length of a String

variable "welcome_message" {
  default = "Hello, Terraform!"
}

output "message_length" {
  value = length(var.welcome_message)
}

Output: 16

The length function returns the total number of characters in the string, including spaces and punctuation.

7. lookup Function

The lookup function is used to retrieve a value from a map based on a given key, with an optional default value if the key is not found. This function is beneficial for handling dynamic values or defaults in your configurations.

Syntax:

lookup(map, key, default)

map: The map from which to retrieve the value.
key: The key to look up.
default: (Optional) The value to return if the key doesn't exist.

Examples:

1. Retrieving a Value from a Map

variable "region_settings" {
  default = {
    us-east-1 = "Virginia"
    us-west-1 = "California"
  }
}

output "selected_region" {
  value = lookup(var.region_settings, "us-east-1", "Unknown")
}

Output: "Virginia"

The lookup function retrieves the value for the key "us-east-1" from the map region_settings.

2. Using a Default Value When the Key Is Missing

output "undefined_region" {
  value = lookup(var.region_settings, "eu-central-1", "Unknown")
}

Output: "Unknown"

Since "eu-central-1" does not exist in the map, the lookup function returns the default value "Unknown".

3. Nested `lookup` Example

variable "settings" {
  default = {
    database = {
      host = "db.example.com"
      port = 5432
    }
  }
}

output "database_host" {
  value = lookup(var.settings["database"], "host", "localhost")
}

Output: "db.example.com"

The lookup function accesses nested map values efficiently.

8. merge Function

The merge function combines two or more maps into a single map. This function is useful when you need to consolidate configurations from multiple sources or override default values with specific ones.

Syntax:

merge(map1, map2, ...)

map1, map2, ...: Two or more maps to be merged into a single map.

Examples:

1. Merging Two Maps

variable "default_config" {
  default = {
    environment = "dev"
    instance_type = "t2.micro"
  }
}

variable "override_config" {
  default = {
    instance_type = "t3.small"
    region        = "us-west-2"
  }
}

output "final_config" {
  value = merge(var.default_config, var.override_config)
}

Output: { environment = "dev" instance_type = "t3.small" region = "us-west-2" }

The merge function combines default_config and override_config, with override_config taking precedence in case of conflicting keys.

2. Merging Multiple Maps

variable "map1" {
  default = {
    a = 1
    b = 2
  }
}

variable "map2" {
  default = {
    b = 3
    c = 4
  }
}

variable "map3" {
  default = {
    d = 5
  }
}

output "combined_map" {
  value = merge(var.map1, var.map2, var.map3)
}

Output: { a = 1 b = 3 c = 4 d = 5 }

The merge function combines all three maps, with later maps (map2 and map3) taking precedence over earlier ones in case of overlapping keys.

3. Using `merge` with Nested Maps

variable "base_settings" {
  default = {
    database = {
      host = "db.local"
      port = 3306
    }
  }
}

variable "additional_settings" {
  default = {
    database = {
      user = "admin"
      password = "secret"
    }
  }
}

output "merged_settings" {
  value = merge(var.base_settings["database"], var.additional_settings["database"])
}

Output: { host = "db.local" port = 3306 user = "admin" password = "secret" }

The merge function combines the nested maps under the database key, creating a more complete configuration.

9. concat Function

The concat function combines multiple lists into a single list. It doesn’t remove duplicates and preserves the order of elements from each list.

Syntax:

concat(list1, list2, ...)

list1, list2, ...: Two or more lists to be concatenated.

Examples:

1. Concatenating Two Lists

variable "list1" {
  default = ["apple", "banana"]
}

variable "list2" {
  default = ["cherry", "date"]
}

output "combined_list" {
  value = concat(var.list1, var.list2)
}

Output: ["apple", "banana", "cherry", "date"]

The concat function combines list1 and list2 into a single list.

2. Concatenating with an Empty List

variable "empty_list" {
  default = []
}

variable "fruits" {
  default = ["grape", "orange"]
}

output "result_list" {
  value = concat(var.empty_list, var.fruits)
}

Output: ["grape", "orange"]

Concatenating an empty list with another list results in just the non-empty list.

3. Concatenating Multiple Lists

variable "list_a" {
  default = ["one", "two"]
}

variable "list_b" {
  default = ["three"]
}

variable "list_c" {
  default = ["four", "five"]
}

output "combined_multiple_lists" {
  value = concat(var.list_a, var.list_b, var.list_c)
}

Output: ["one", "two", "three", "four", "five"]

Multiple lists are combined into one ordered list.

10. flatten Function

The flatten function is used to convert a nested list (a list of lists) into a single, flat list. It's useful for removing nested layers when you need a single-level list.

Syntax:

flatten(list)

list: The nested list you want to flatten.

Examples:

1. Flattening a Simple Nested List

variable "nested_list" {
  default = [["a", "b"], ["c", "d"], ["e"]]
}

output "flat_list" {
  value = flatten(var.nested_list)
}

Output: ["a", "b", "c", "d", "e"]

The flatten function removes the inner list structure, resulting in a single-level list.

2. Flattening Lists with Empty Lists

variable "mixed_nested_list" {
  default = [["apple", "banana"], [], ["cherry"]]
}

output "flattened_result" {
  value = flatten(var.mixed_nested_list)
}

Output: ["apple", "banana", "cherry"]

Empty lists within the nested list are ignored, resulting in a flat list.

3. Flattening Multiple Levels of Nesting

variable "deep_nested_list" {
  default = [[[1, 2]], [3, 4], [5]]
}

output "flat_deep_list" {
  value = flatten(flatten(var.deep_nested_list))
}

Output: [1, 2, 3, 4, 5]

Applying flatten multiple times can help when there are multiple levels of nesting.

11. slice Function

The slice function extracts a sublist from a given list, using start and end index values.

Syntax:

slice(list, start, end)

list: The list to slice.
start: The start index (inclusive).
end: The end index (exclusive).

Examples:

1. Slicing a List from Index 1 to 3

variable "numbers" {
  default = [10, 20, 30, 40, 50]
}

output "sliced_list" {
  value = slice(var.numbers, 1, 3)
}

Output: [20, 30]

The slice function extracts elements from index 1 to 3 (excluding 3).

2. Slicing to the End of a List

output "slice_to_end" {
  value = slice(var.numbers, 2, length(var.numbers))
}

Output: [30, 40, 50]

Using length(var.numbers) as the end index slices the list up to the last element.

3. Handling Negative Indices

output "negative_slice" {
  value = slice(var.numbers, -3, -1)
}

Output: [30, 40]

Negative indices count from the end of the list.

12. zipmap Function

The zipmap function creates a map by combining two lists: one for the keys and another for the values. It’s useful when you want to transform two related lists into a key-value structure.

Syntax:

zipmap(keys, values)

keys: A list of keys.
values: A list of values corresponding to each key.

Examples:

1. Creating a Simple Map

variable "keys" {
  default = ["name", "age", "city"]
}

variable "values" {
  default = ["Alice", 30, "New York"]
}

output "person_map" {
  value = zipmap(var.keys, var.values)
}

Output: { "name" = "Alice" "age" = 30 "city" = "New York" }

The zipmap function combines keys and values into a map.

2. Handling Lists of Different Lengths

If the keys list is longer than the values list, zipmap fills the missing values with null.

variable "keys_extra" {
  default = ["one", "two", "three", "four"]
}

variable "values_short" {
  default = [1, 2]
}

output "mismatched_zipmap" {
  value = zipmap(var.keys_extra, var.values_short)
}

Output: { "one" = 1 "two" = 2 "three" = null "four" = null }

The additional keys are paired with null values.

3. Using `zipmap` with Computed Values

variable "countries" {
  default = ["USA", "Canada", "Mexico"]
}

variable "codes" {
  default = ["US", "CA", "MX"]
}

output "country_code_map" {
  value = zipmap(var.countries, var.codes)
}

Output: { "USA" = "US" "Canada" = "CA" "Mexico" = "MX" }

The zipmap function efficiently maps country names to their respective codes.

13. Working with key and value in Maps

In Terraform, you often need to work with keys and values from maps. Although there's no direct key or value function, you can use the keys() and values() functions to extract all keys or values from a map, respectively.

a. `keys` Function

The keys function retrieves all keys from a given map as a list.

Syntax:

keys(map)

map: The map from which you want to extract keys.

Example:

Extracting Keys

variable "server_config" {
  default = {
    instance_type = "t2.micro"
    region        = "us-east-1"
    availability  = "zone-a"
  }
}

output "config_keys" {
  value = keys(var.server_config)
}

Output: ["instance_type", "region", "availability"]

This returns all the keys from the server_config map as a list.

b. `values` Function

The values function retrieves all values from a given map as a list.

Syntax:

values(map)

map: The map from which you want to extract values.

Example:

Extracting Values

output "config_values" {
  value = values(var.server_config)
}

Output: ["t2.micro", "us-east-1", "zone-a"]

This returns all the values from the server_config map as a list.

14. element Function

The element function retrieves an item from a list based on its index. If the index is out of range, it wraps around using the modulo operation.

Syntax:

element(list, index)

list: The list from which you want to retrieve an element.
index: The position of the element you want to access.

Examples:

1. Basic Element Access

variable "fruit_list" {
  default = ["apple", "banana", "cherry"]
}

output "second_element" {
  value = element(var.fruit_list, 1)
}

Output: "banana"

The element at index 1 in the list is "banana".

2. Accessing Out-of-Bounds Index

output "wrapped_index" {
  value = element(var.fruit_list, 4)
}

Output: "banana"

Index 4 wraps around to 1 (4 % 3 = 1).

15. index Function

The index function returns the position of a given value within a list. If the value isn't found, it throws an error.

Syntax:

index(list, value)

list: The list to search.
value: The value you want to find.

Examples:

1. Finding the Index of a Value

variable "colors" {
  default = ["red", "green", "blue"]
}

output "index_of_green" {
  value = index(var.colors, "green")
}

Output: 1

"green" is located at index 1.

2. Value Not Found

output "index_of_yellow" {
  value = index(var.colors, "yellow")
}

Error: The index function will throw an error because "yellow" isn't in the list.

16. contains Function

The contains function checks if a list contains a specific value and returns true or false.

Syntax:

contains(list, value)

list: The list to search.
value: The value to check.

Examples:

1. Checking for Presence

variable "animals" {
  default = ["cat", "dog", "bird"]
}

output "contains_dog" {
  value = contains(var.animals, "dog")
}

Output: true

"dog" is in the list, so contains returns true.

2. Value Not Present

output "contains_fish" {
  value = contains(var.animals, "fish")
}

Output: false

"fish" isn't in the list, resulting in false.

17. distinct Function

The distinct function removes duplicate values from a list and returns a new list with only unique elements.

Syntax:

distinct(list)

list: The list from which duplicates should be removed.

Examples:

1. Removing Duplicates

variable "numbers" {
  default = [1, 2, 2, 3, 4, 4, 5]
}

output "unique_numbers" {
  value = distinct(var.numbers)
}

Output: [1, 2, 3, 4, 5]

The distinct function removes the duplicate 2 and 4 values.

2. Handling Lists with All Unique Elements

variable "unique_list" {
  default = ["apple", "banana", "cherry"]
}

output "still_unique" {
  value = distinct(var.unique_list)
}

Output: ["apple", "banana", "cherry"]

The list remains unchanged as all elements are already unique.

Let's explore the coalesce, coalescelist, and one functions in Terraform, complete with detailed explanations, syntax, and examples.

18. coalesce Function

The coalesce function returns the first non-null value from a list of arguments. This is particularly useful for setting default values or handling optional variables.

Syntax:

coalesce(value1, value2, ...)

value1, value2, ...: A list of values to evaluate. The function returns the first value that is not null.

Examples:

1. Basic Coalesce Usage

variable "var1" {
  default = null
}

variable "var2" {
  default = "default_value"
}

output "first_non_null" {
  value = coalesce(var.var1, var.var2, "fallback_value")
}

Output: "default_value"

The function returns var2 because it is the first non-null value.

2. All Values Null

variable "var3" {
  default = null
}

output "all_null" {
  value = coalesce(var.var1, var.var3)
}

Output: null

Since all values are null, the result is null.

19. coalescelist Function

The coalescelist function is similar to coalesce, but it works with lists. It returns the first non-empty list from a list of lists.

Syntax:

coalescelist(list1, list2, ...)

list1, list2, ...: A list of lists to evaluate. The function returns the first non-empty list.

Examples:

1. Basic Coalescelist Usage

variable "list1" {
  default = []
}

variable "list2" {
  default = ["apple", "banana"]
}

output "first_non_empty_list" {
  value = coalescelist(var.list1, var.list2, ["fallback"])
}

Output: ["apple", "banana"]

The function returns list2 as it is the first non-empty list.

2. All Lists Empty

variable "empty_list1" {
  default = []
}

variable "empty_list2" {
  default = []
}

output "all_empty_lists" {
  value = coalescelist(var.empty_list1, var.empty_list2)
}

Output: []

Since all lists are empty, the result is an empty list.

20. one Function

The one function checks if exactly one of its arguments is non-null and returns that value. If none or more than one argument is non-null, it results in an error.

Syntax:

one(value1, value2, ...)

value1, value2, ...: A list of values to evaluate. It checks if exactly one is non-null.

Examples:

1. Basic One Usage

variable "single_value" {
  default = "only_value"
}

output "exactly_one_non_null" {
  value = one(var.single_value, null)
}

Output: "only_value"

The function returns single_value because it is the only non-null value.

2. More than One Non-Null

variable "var4" {
  default = "value_1"
}

variable "var5" {
  default = "value_2"
}

output "more_than_one_non_null" {
  value = one(var.var4, var.var5)
}

Error: The function will throw an error because there are two non-null values.

3. No Non-Null Values

output "no_non_null" {
  value = one(null, null)
}

Error: The function will throw an error because there are no non-null values.

21. try Function

The try function is a powerful utility that attempts to evaluate a list of expressions in order. It returns the result of the first expression that does not produce an error. This is particularly useful for error handling and providing fallback values when working with resources or variables that may not always be available.

Syntax:

try(expression1, expression2, ...)

expression1, expression2, ...: A list of expressions to evaluate in order. The function returns the result of the first expression that succeeds without error.

Examples:

1. Basic Try Usage

variable "valid_variable" {
  default = "I am valid"
}

variable "invalid_variable" {
  default = null
}

output "try_example" {
  value = try(var.valid_variable, var.invalid_variable, "Fallback Value")
}

Output: "I am valid"

In this case, try returns var.valid_variable since it successfully evaluates without error.

2. Handling Errors Gracefully

output "handle_errors" {
  value = try(length(var.invalid_variable), "Length calculation failed")
}

Output: "Length calculation failed"

Here, the length function fails because var.invalid_variable is null, so try returns the fallback string instead of throwing an error.

3. Multiple Expressions

variable "input_value" {
  default = null
}

output "multiple_expressions" {
  value = try(length(var.input_value), var.valid_variable, "Fallback Result")
}

Output: "I am valid"

try first attempts to get the length of var.input_value, which is null (and fails), then it evaluates var.valid_variable, which succeeds.

4. All Expressions Fail

output "all_fail" {
  value = try(null, null, null, "All expressions failed")
}

Output: "All expressions failed"

Since all provided expressions fail, try returns the final fallback string.

22. can Function

The can function is a useful utility in Terraform that determines whether an expression can be evaluated without causing an error. It returns a boolean value: true if the expression can be evaluated without errors, and false otherwise. This function is particularly helpful for conditional logic and error handling.

Syntax:

can(expression)

expression: The expression you want to evaluate. If the expression can be executed without causing an error, can returns true; otherwise, it returns false.

Examples:

1. Basic Can Usage

variable "valid_input" {
  default = "Hello, Terraform!"
}

output "is_valid" {
  value = can(length(var.valid_input))
}

Output: true

The length function successfully evaluates the valid string, so can returns true.

2. Evaluating a Null Variable

variable "null_input" {
  default = null
}

output "is_null" {
  value = can(length(var.null_input))
}

Output: false

The length function cannot evaluate a null variable, so can returns false.

3. Using Can in Conditional Logic

variable "optional_value" {
  default = null
}

output "conditional_message" {
  value = can(var.optional_value) ? "Value is present" : "Value is absent"
}

Output: "Value is absent"

Here, can checks if var.optional_value is valid. Since it is null, the output reflects that the value is absent.

4. Checking Function Calls

output "check_function" {
  value = can(1 / 0) ? "No error" : "Error occurred"
}

Output: "Error occurred"

Division by zero would normally cause an error, but can captures this and returns false, allowing the output to indicate an error occurred.

23. file Function

The file function reads the contents of a file and returns it as a string. This function is useful for including configuration files, scripts, or other text-based resources directly into your Terraform configurations.

Syntax:

file(path)

path: The relative or absolute path to the file you want to read.

Examples:

1. Basic File Usage

Assuming you have a file named example.txt with the content Hello, Terraform!.

output "file_content" {
  value = file("example.txt")
}

Output: "Hello, Terraform!"

The file function reads the contents of example.txt and returns it as a string.

2. Reading a Configuration File

output "config_content" {
  value = file("${path.module}/config.json")
}

Output: (Content of config.json)

This example reads the contents of a JSON configuration file located in the same directory as the Terraform module.

3. Error Handling

If the specified file does not exist:

output "missing_file" {
  value = file("missing.txt")
}

Error: This will throw an error indicating that the file does not exist.

24. templatefile Function

The templatefile function renders a template file using variables provided in a map. This is particularly useful for creating dynamic configurations where you need to substitute values into a template.

Syntax:

templatefile(path, vars)

path: The path to the template file.
vars: A map of variables to substitute in the template.

Examples:

1. Basic Templatefile Usage

Assuming you have a template file named greeting.tmpl with the following content:

Hello, ${name}!

You can use templatefile like this:

variable "user_name" {
  default = "Terraform User"
}

output "greeting" {
  value = templatefile("greeting.tmpl", { name = var.user_name })
}

Output: "Hello, Terraform User!"

The templatefile function substitutes the ${name} placeholder in the template with the value of var.user_name.

2. Using Multiple Variables

Assuming a template file config.tmpl:

{
  "region": "${region}",
  "instance_type": "${instance_type}"
}

You can render it like this:

output "config" {
  value = templatefile("config.tmpl", { region = "us-east-1", instance_type = "t2.micro" })
}

Output:

{
  "region": "us-east-1",
  "instance_type": "t2.micro"
}

This example substitutes multiple variables in a JSON configuration template.

3. Error Handling

If the specified template file does not exist:

output "missing_template" {
  value = templatefile("missing.tmpl", { name = "User" })
}

Error: This will throw an error indicating that the template file does not exist.

25. Base64 Functions: base64encode and base64decode

Terraform provides two essential functions for handling data in base64 format: base64encode and base64decode. These functions are crucial for encoding sensitive information like passwords and decoding data for use in your configurations.

25a. `base64encode` Function

The base64encode function encodes a string into base64 format, making it suitable for securely handling sensitive data.

Syntax

base64encode(string)

Parameters:
- string: The string you want to encode in base64 format.

Examples

1. Basic Usage

output "encoded_string" {
  value = base64encode("Hello, Terraform!")
}

Output:

"SGVsbG8sIFRlcmFmb3JtIQ=="

Encodes the string Hello, Terraform! into base64 format.

2. Encoding Sensitive Data

variable "secret_password" {
  default = "my_secret_password"
}

output "encoded_password" {
  value = base64encode(var.secret_password)
}

Output:

"bXlfc2VjcmV0X3Bhc3N3b3Jk"

Encodes the sensitive password for secure storage.

3. Encoding JSON Data

variable "json_data" {
  default = "{\"key\":\"value\"}"
}

output "encoded_json" {
  value = base64encode(var.json_data)
}

Output:

"eyJrZXkiOiJ2YWx1ZSJ9"

Encodes a JSON string into base64 format.

25b. `base64decode` Function

The base64decode function decodes a base64-encoded string back to its original form, allowing you to safely retrieve sensitive data.

Syntax

base64decode(string)

Parameters:
- string: The base64-encoded string to decode.

Examples

1. Basic Usage

output "decoded_string" {
  value = base64decode("SGVsbG8sIFRlcmFmb3JtIQ==")
}

Output:

"Hello, Terraform!"

Decodes the base64 string back to the original text.

2. Decoding Sensitive Data

variable "encoded_password" {
  default = "bXlfc2VjcmV0X3Bhc3N3b3Jk"  # base64 for "my_secret_password"
}

output "decoded_password" {
  value = base64decode(var.encoded_password)
}

Output:

"my_secret_password"

Retrieves the original password from its encoded form.

3. Decoding JSON Data

variable "encoded_json" {
  default = "eyJrZXkiOiJ2YWx1ZSJ9"  # base64 for '{"key":"value"}'
}

output "decoded_json" {
  value = base64decode(var.encoded_json)
}

Output:

{"key":"value"}

Decodes the base64-encoded JSON data back to its original format.

26. JSON Functions: jsonencode and jsondecode

Terraform provides two powerful functions for working with JSON data: jsonencode and jsondecode. These functions simplify the process of converting Terraform data structures to JSON format and vice versa, making it easier to manage configuration data.

26a. `jsonencode` Function

The jsonencode function converts a Terraform data structure into its JSON representation. This is particularly useful for generating JSON-formatted outputs or passing data to APIs.

Syntax

jsonencode(value)

Parameters:
- value: The Terraform data structure (map, list, string, number, etc.) that you want to convert to JSON.

Examples

1. Basic Usage

variable "my_map" {
  default = {
    key1 = "value1"
    key2 = "value2"
  }
}

output "json_output" {
  value = jsonencode(var.my_map)
}

Output:

{"key1":"value1","key2":"value2"}

Converts the Terraform map into a JSON string.

2. Encoding Lists

variable "my_list" {
  default = ["apple", "banana", "cherry"]
}

output "json_list" {
  value = jsonencode(var.my_list)
}

Output:

["apple","banana","cherry"]

Converts a list of fruits into a JSON array.

3. Complex Data Structures

variable "complex_data" {
  default = {
    name = "John Doe"
    age  = 30
    tags = ["developer", "terraform"]
  }
}

output "json_complex" {
  value = jsonencode(var.complex_data)
}

Output:

{"name":"John Doe","age":30,"tags":["developer","terraform"]}

Encodes a complex data structure with multiple types into JSON.

26b. `jsondecode` Function

The jsondecode function takes a JSON-formatted string and converts it back into a Terraform data structure. This is useful for working with JSON data from external sources, like APIs or configuration files.

Syntax

jsondecode(json)

Parameters:
- json: The JSON string that you want to decode into a Terraform data structure.

Examples

1. Basic Usage

variable "json_string" {
  default = "{\"key\":\"value\"}"
}

output "decoded_map" {
  value = jsondecode(var.json_string)
}

Output:

{
  key = "value"
}

Decodes the JSON string into a Terraform map.

2. Decoding Lists

variable "json_list" {
  default = "[\"apple\", \"banana\", \"cherry\"]"
}

output "decoded_list" {
  value = jsondecode(var.json_list)
}

Output:

["apple", "banana", "cherry"]

Converts the JSON array back into a Terraform list.

3. Decoding Complex JSON

variable "json_complex" {
  default = "{\"name\":\"John Doe\", \"age\":30, \"tags\":[\"developer\", \"terraform\"]}"
}

output "decoded_complex" {
  value = jsondecode(var.json_complex)
}

Output:

{
  name = "John Doe"
  age  = 30
  tags = ["developer", "terraform"]
}

Converts complex JSON data back into a Terraform map.

Here’s the combined layout for yamlencode and yamldecode, formatted similarly to the previous sections:

27. YAML Functions: yamlencode and yamldecode

Terraform includes two handy functions for working with YAML data: yamlencode and yamldecode. These functions facilitate the conversion between Terraform data structures and YAML format, making it easier to manage configurations that require YAML representation.

27a. `yamlencode` Function

The yamlencode function converts a Terraform data structure into its YAML representation. This is particularly useful when you need to generate YAML outputs for configuration files or documentation.

Syntax

yamlencode(value)

Parameters:
- value: The Terraform data structure (map, list, string, number, etc.) that you want to convert to YAML.

Examples

1. Basic Usage

variable "my_map" {
  default = {
    key1 = "value1"
    key2 = "value2"
  }
}

output "yaml_output" {
  value = yamlencode(var.my_map)
}

Output:

key1: value1
key2: value2

Converts the Terraform map into a YAML string.

2. Encoding Lists

variable "my_list" {
  default = ["apple", "banana", "cherry"]
}

output "yaml_list" {
  value = yamlencode(var.my_list)
}

Output:

- apple
- banana
- cherry

Converts a list of fruits into a YAML sequence.

3. Complex Data Structures

variable "complex_data" {
  default = {
    name = "John Doe"
    age  = 30
    tags = ["developer", "terraform"]
  }
}

output "yaml_complex" {
  value = yamlencode(var.complex_data)
}

Output:

age: 30
name: John Doe
tags:
- developer
- terraform

Encodes a complex data structure with multiple types into YAML.

27b. `yamldecode` Function

The yamldecode function takes a YAML-formatted string and converts it back into a Terraform data structure. This is useful for working with YAML data from external sources, like configuration files or APIs.

Syntax

yamldecode(yaml)

Parameters:
- yaml: The YAML string that you want to decode into a Terraform data structure.

Examples

1. Basic Usage

variable "yaml_string" {
  default = "key: value"
}

output "decoded_map" {
  value = yamldecode(var.yaml_string)
}

Output:

{
  key = "value"
}

Decodes the YAML string into a Terraform map.

2. Decoding Lists

variable "yaml_list" {
  default = "- apple\n- banana\n- cherry"
}

output "decoded_list" {
  value = yamldecode(var.yaml_list)
}

Output:

["apple", "banana", "cherry"]

Converts the YAML sequence back into a Terraform list.

3. Decoding Complex YAML

variable "yaml_complex" {
  default = "name: John Doe\nage: 30\ntags:\n  - developer\n  - terraform"
}

output "decoded_complex" {
  value = yamldecode(var.yaml_complex)
}

Output:

{
  name = "John Doe"
  age  = 30
  tags = ["developer", "terraform"]
}

Converts complex YAML data back into a Terraform map.

Final Thoughts

In conclusion, mastering Terraform's built-in functions can greatly enhance your infrastructure management. These functions streamline your workflows, reduce complexity, and allow you to write cleaner and more efficient code.

From data manipulation to seamless conversions between JSON and YAML, each function empowers you to automate and manage your resources effectively. Whether you're a beginner or an experienced user, leveraging these capabilities will transform your approach to infrastructure as code.

Embrace these tools, experiment with them, and elevate your Terraform journey to new heights. Happy coding!

Top comments (2)

Brian Clarke • Oct 1

As usual, very informative and useful.

Panchanan Panigrahi • Oct 1

Thank you for the kind words! I'm glad you found it informative and useful. Your feedback means a lot!

What are Terraform Functions?

1. toset Function

Syntax:

Example:

2. format Function

Syntax:

Supported Placeholders:

Examples:

1. Formatting Strings

2. Formatting Integers

3. Formatting Floats

4. Boolean Values

5. Using Automatic Formatting with %v

3. formatlist Function

Syntax:

Supported Placeholders:

Examples:

1. Formatting a List of Strings

2. Formatting a List of Integers

3. Formatting a List of Floats

4. Using Automatic Formatting with %v in Lists

4. join Function

Syntax:

Examples:

1. Joining a List of Strings

2. Joining with No Delimiter

3. Joining Integers (Converted to Strings)

5. split Function

Syntax:

Examples:

1. Splitting a Comma-Separated String

2. Splitting a String with Spaces

3. Splitting with a Complex Delimiter

4. Splitting a String and Joining Again

6. length Function

Syntax:

Examples:

1. Finding the Length of a List

2. Determining the Length of a Map

3. Calculating the Length of a String

7. lookup Function

Syntax:

Examples:

1. Retrieving a Value from a Map

2. Using a Default Value When the Key Is Missing

3. Nested lookup Example

8. merge Function

Syntax:

Examples:

1. Merging Two Maps

2. Merging Multiple Maps

3. Using merge with Nested Maps

9. concat Function

Syntax:

Examples:

1. Concatenating Two Lists

2. Concatenating with an Empty List

3. Concatenating Multiple Lists

10. flatten Function

Syntax:

Examples:

1. Flattening a Simple Nested List

2. Flattening Lists with Empty Lists

3. Flattening Multiple Levels of Nesting

11. slice Function

Syntax:

Examples:

1. Slicing a List from Index 1 to 3

2. Slicing to the End of a List

3. Handling Negative Indices

12. zipmap Function

Syntax:

Examples:

1. Creating a Simple Map

2. Handling Lists of Different Lengths

3. Using zipmap with Computed Values

13. Working with key and value in Maps

a. keys Function

Syntax:

Example:

5. Using Automatic Formatting with `%v`

4. Using Automatic Formatting with `%v` in Lists

3. Nested `lookup` Example

3. Using `merge` with Nested Maps

3. Using `zipmap` with Computed Values

a. `keys` Function

b. `values` Function