Terraform Expressions

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Terraform Expressions

They can be categorised into three segments:

1. Conditional expressions

2. Dynamic blocks

3. Splat expressions

Conditional Expressions

Conditional expressions in Terraform use a ternary-like syntax: condition ? true_value : false_value. This is useful for setting resource attributes, variables, or outputs based on conditions.​

• Example:

    # first we check var.environment is "dev" if yes we assign textbucket_name to "dev-bucket"
    # else we store "prod-bucket"
    textbucket_name = var.environment == "dev" ? "dev-bucket" : "prod-bucket"
  

• You can combine conditions using logical operators (&&, ||, !).

• Conditional expressions are often used with count, for_each, modules, locals, and outputs to control resource creation or attribute values.​

Dynamic Blocks

Dynamic blocks allow you to generate repeated nested blocks (like security_rule in Azure or ingress in AWS) based on lists or maps. This avoids duplicating configuration.​

• Syntax:

    textdynamic "block_name" {
      for_each = local.list_of_rules
      content {
        name        = block_name.value.name
        priority    = block_name.value.priority
        # ... other attributes
      }
    }
  

• Useful for managing multiple similar blocks, such as security rules, tags, or network settings.

Splat Expressions

Splat expressions ([*]) simplify extracting attributes from lists of objects.​

• Example:
  If you have a list of objects:

    textlocals {
      users = [
        { name = "Alice", role = "admin" },
        { name = "Bob",   role = "user" }
      ]
    }
  

  You can extract all names with:

    textlocal.names = local.users[*].name
  

• Splat expressions work with both lists and maps, and can be used in for_each or as arguments.​

These expressions make Terraform configurations more flexible, reusable, and easier to maintain, especially when dealing with variable environments or complex resource structures.​

Check out more examples here.

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Arigato!