When you define variables and values in Terraform, each one has a data type: it indicates what kind of information it contains (a text, a number, a list…). Knowing the types helps you write correct code and understand the examples you find. It’s a simple topic and very similar to the types in any programming language.

Declaring the type of a variable has two advantages:

1. Clarity: whoever reads the code knows what each variable expects.
2. Validation: Terraform warns you if you pass a value of the wrong type (for example, a text where a number was expected), preventing errors.

Types are divided into simple (a single value) and complex (collections of values).

Any text, in double quotes.

Examples of values: "hello", "t3.micro", "eu-west-1".

Numbers, integers or decimals, without quotes.

Examples: 3, 0, 2.5, 100.

A logical value: true or false. Useful for enabling/disabling things.

Usage example: a bool variable can decide whether a resource is created or not, or whether an option is enabled. For example, “enable Multi-AZ in the database? true/false”.

These group several values. They are very useful for real configurations.

A sequence of values of the same type, in order, in brackets [ ].

This is a list of texts. list(string) means “a list of strings”. You access its elements by position (starting at 0): the first is var.zonas_disponibilidad[0].

Real example: a list of the availability zones where you want to deploy (remember Chapter 3), or a list of ports to open.

A collection of “key = value” pairs, in braces { }. Like a dictionary where you look up a value by its key.

You access a value by its key: var.tipos_por_entorno["prod"] returns "m5.large".

Real example: assign a different instance size to each environment, or a set of tags for your resources.

An object groups several values of different types under specific field names. It’s like a record with fields.

You access a field with a dot: var.config_servidor.tipo returns "t3.micro".

Difference map vs object:

• A map has free keys and all values of the same type.
• An object has predefined fields with specific names and types (which can be different from each other).

• If you’re not sure about the type, there’s any (accepts any type), but it’s better to be specific when you can.
• If you don’t declare the type, Terraform often infers it from the default value. Even so, declaring the type is good practice because it documents and validates.

Here a single object describes the entire configuration of a network: its range (string), its zones (list), whether it has NAT (bool), and its tags (map). This is very similar to how things are configured in real projects.

• Every value in Terraform has a type. Declaring it provides clarity and validation.
• Simple types: string (text), number (numbers), bool (true/false).
• Complex types: list (ordered list of the same type), map (key-value pairs of the same type), object (structure with defined fields of different types).
• map vs object: map has free keys and values of the same type; object has predefined fields with specific types.
• Declaring types is good practice, even though Terraform sometimes infers them.

In the next subchapter we’ll see how to work with these values using expressions, references, and built-in Terraform functions.