Conditional Logic for Cloud-Specific Resources in Terraform

When managing infrastructure across multiple cloud providers (multi-cloud), you often need to provision resources that are specific to a particular cloud. Terraform's conditional logic allows you to dynamically include or exclude resources based on variables, making your configurations more flexible and reusable.

The `count` Meta-Argument

One of the primary ways to implement conditional resource creation is by using the

code

count

meta-argument. By setting

code

count

code

based on a condition, you can effectively enable or disable the creation of a resource block.

`count` controls resource instantiation based on a numerical value.

Setting count to 0 means the resource will not be created. Setting it to 1 (or any positive integer) will create that many instances of the resource. This is perfect for conditional logic.

The count meta-argument accepts an integer. If count is 0, Terraform will not create any instances of that resource. If count is greater than 0, Terraform will create that many instances. This behavior is leveraged to conditionally create resources. For example, you can set count = var.create_resource ? 1 : 0, where var.create_resource is a boolean variable. If var.create_resource is true, count becomes 1, and the resource is created. If it's false, count becomes 0, and the resource is skipped.

What value of the count meta-argument prevents a resource from being created?

Using `for_each` for Conditional Resource Sets

While

code

count

is excellent for conditionally creating a single resource,

code

for_each

is more powerful when you need to conditionally create multiple resources based on a map or set.

`for_each` iterates over a collection to create resources conditionally.

You can filter a map or set before passing it to for_each to control which resources are created. This is useful for provisioning cloud-specific services based on an environment variable.

The for_each meta-argument iterates over a map or a set of strings. To achieve conditional creation, you can use Terraform's built-in functions like for expressions to filter the collection based on your conditions. For instance, if you have a map of cloud provider configurations and you only want to create resources for a specific provider, you can filter the map before passing it to for_each. This allows for more dynamic and scalable conditional resource management.

Conditional Resource Blocks with `if` Statements (Terraform 0.15+)

Terraform 0.15 introduced the ability to use

code

if

statements directly within resource blocks, offering a more declarative way to handle conditional resource creation.

Direct `if` statements simplify conditional resource inclusion.

This syntax allows you to specify a condition directly within the resource block, making the intent clearer and the code more readable for cloud-specific resource provisioning.

With Terraform 0.15 and later, you can use an if statement directly within a resource block. This is particularly useful for cloud-specific configurations. For example, you might have a variable cloud_provider set to 'aws' or 'azure'. You can then define a resource block that only applies if cloud_provider matches a specific value. This approach avoids the need for complex count or for_each logic in simpler conditional scenarios, enhancing code clarity.

Consider a scenario where you need to create an AWS S3 bucket or an Azure Blob Storage container based on a variable cloud_provider. Using count with a ternary operator is a common pattern. If cloud_provider is 'aws', count is 1, creating the S3 bucket. If cloud_provider is 'azure', count is 0, skipping the S3 bucket. The reverse would be true for an Azure Blob Storage resource. This demonstrates how conditional logic dynamically selects which cloud-specific resources are provisioned.

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Conditional Configuration Values

Beyond just creating or skipping resources, conditional logic can also be used to set different configuration values for resources based on the cloud provider or environment.

Ternary operators and conditional expressions tailor resource attributes.

You can use ternary operators (condition ? true_val : false_val) or lookup with default values to dynamically set attributes like instance types, region names, or network configurations based on your chosen cloud provider.

For instance, an EC2 instance might need a different ami value in AWS than a Virtual Machine in Azure. You can use a ternary operator within the resource block to select the correct AMI ID based on a cloud_provider variable. Similarly, network settings, storage tiers, or naming conventions can be made cloud-specific using these conditional expressions, ensuring your infrastructure adapts to the nuances of each cloud platform.

When working with multi-cloud, always define your conditional logic clearly in variables and use descriptive names to ensure your infrastructure remains understandable and maintainable.

Best Practices for Multi-Cloud Conditional Logic

Effective use of conditional logic in multi-cloud environments requires careful planning and adherence to best practices.

Technique	Use Case	Complexity	Readability
`count`	Conditionally create/destroy a single resource.	Low to Medium	Good
`for_each`	Conditionally create multiple resources from a collection.	Medium to High	Good (with clear filtering)
Direct `if` (0.15+)	Conditionally include/exclude entire resource blocks.	Low	Excellent
Conditional Attributes	Dynamically set resource arguments.	Low to Medium	Good

Leveraging these techniques allows for robust, adaptable, and efficient multi-cloud infrastructure management with Terraform.

Learning Resources

Terraform Documentation: Conditional Logic(documentation)

Official HashiCorp documentation explaining the `count` meta-argument and its use in conditional resource creation.

Terraform Documentation: `for_each` Meta-Argument(documentation)

Learn how to use `for_each` to provision multiple resources based on a map or set, crucial for conditional multi-cloud deployments.

Terraform 0.15 Release Notes: `if` Statements(blog)

Details on the new `if` statement syntax introduced in Terraform 0.15, simplifying conditional resource inclusion.

Terraform Conditional Expressions Tutorial(blog)

A practical guide on using conditional expressions and ternary operators in Terraform for dynamic configurations.

Multi-Cloud Infrastructure with Terraform(documentation)

An overview from HashiCorp on strategies for managing infrastructure across multiple cloud providers using Terraform.

Terraform `for` Expressions(documentation)

Understand Terraform's `for` expressions, which are powerful for filtering and transforming collections used with `for_each`.

Terraform Variables Guide(documentation)

Essential reading on defining and using variables in Terraform, which are the foundation for conditional logic.

Terraform `lookup` Function(documentation)

Learn about the `lookup` function, useful for retrieving values from maps with a fallback, aiding conditional attribute setting.

Building Reusable Terraform Modules for Multi-Cloud(blog)

Tips and strategies for creating modular Terraform code that can be adapted for different cloud environments.

Terraform `templatefile` Function(documentation)

Explore how `templatefile` can be used to dynamically generate configuration files, which can incorporate conditional logic.