Leveraging Nested Stacks for Dividing AWS CloudFormation Templates

Overview

AWS CloudFormation allows you to define and provision infrastructure resources as code using templates. These templates are typically written in JSON or YAML format. When working with complex infrastructure setups, breaking down your templates into smaller, more manageable pieces is common. Nested stacks are a feature in AWS CloudFormation that allows you to achieve this modularity and reusability. 

In this blog, we’ll walk you through creating a template that calls another template that can generate a resource.

Introduction

AWS CloudFormation is a service provided by Amazon Web Services (AWS) that allows users to define and provision AWS resources in a predictable and repeatable way. With AWS CloudFormation, you can model your entire infrastructure based on code, creating resources, reducing manual work, and simplifying and exporting applications.

AWS CloudFormation, at its core, uses templates, often written in YAML or JSON, to define AWS processes and their relationships. After you create the template, AWS CloudFormation manages and configures these resources for you. This ensures that your infrastructure is set up consistently, reducing errors and inconsistencies during setup.

Benefits of AWS CloudFormation

• Infrastructure as Code (IaC): AWS CloudFormation allows you to define your processes in code that can be modified, reviewed and shared like any other software code. This makes the management and delivery process reliable and efficient.
• Auto Configuration: AWS CloudFormation automates the configuration process. You define the desired state of your process in the model, and AWS CloudFormation creates, updates, and removes the resources needed to reach that state.
• Consistency and Repeatability: With AWS CloudFormation, you can make your infrastructure consistent across environments (development, test, production) and regions. This helps prevent configuration drift and ensure environmental repeatability.
• Scalability: AWS CloudFormation makes it easy to build architectures with many resources. By defining models with various services and integrations, you can make it easy to scale up or down when the application needs to change.
• Dependency Management: AWS CloudFormation manages dependencies between resources, ensuring that they are created correctly and have access to the information needed.
• Change Management: AWS CloudFormation monitors changes in real-time. When you change your model, AWS CloudFormation can identify what needs to be updated and apply those changes with minimal downtime.

When using AWS CloudFormation, the complexity of your models increases as your processes grow. One way to overcome this complexity is to use nested stacks to break the build into smaller, more manageable chunks.

Nested Stacks

Nested stacks in AWS CloudFormation are a feature that allows you to create a parent-child relationship between different AWS CloudFormation stacks. This enables you to break down a complex infrastructure deployment into smaller, more manageable components. A nested stack is essentially an AWS CloudFormation stack that is used as a resource within another AWS CloudFormation stack.

Benefits of Nested Stacks

• Modularity and Separation of Concerns: Nested stacks allow you to break down a large and complex AWS CloudFormation template into smaller, more manageable components. Each nested stack can represent a specific logical unit of your architecture, such as different tiers or modules of your application.
• Reusability: You can reuse the same nested stack across multiple parent stacks. This is particularly beneficial when you share common infrastructure patterns across various projects or environments. Changes made to a reusable nested stack are automatically propagated to all parent stacks that use it.
• Encapsulation: Nested stacks encapsulate resources and configurations within a clear boundary. This isolation helps prevent resource naming conflicts, reduces resource dependency, and simplifies troubleshooting.
• Parallel Deployment: When deploying a parent stack with multiple nested stacks, CloudFormation can deploy the nested stacks in parallel. This can significantly speed up the deployment process and reduce overall provisioning time.
• Granular Updates: You can update individual nested stacks without affecting the entire architecture. If you need to change a specific part of your infrastructure, you can focus on updating the relevant nested stack rather than the entire application stack.
• Versioning and Rollbacks: Each nested stack can have its own versioning and rollback mechanisms. This allows you to roll back a specific nested stack to a previous version if an issue arises, minimizing the impact on the rest of your infrastructure.
• Testing and Validation: You can test individual nested stacks separately, which can simplify the process of validating changes and configurations before applying them to the entire application.
• Infrastructure as Code Best Practices: Nested stacks align with the best practices of Infrastructure as Code (IaC). You can version-control your nested stack templates, apply code review processes, and improve the overall reliability and reproducibility of your deployments.

Step-by-Step Guide to Use Nested Stacks

Here’s how you can use nested stacks in AWS CloudFormation templates:

• Create the Parent Stack Template:

Your main template, often called the “parent” stack, will include references to the nested stacks. It can be written in JSON or YAML format. This is where you define the parameters, resources, and outputs for your entire infrastructure.

• Create the Nested Stack Template:

• Deploy the Parent Stack:

Here, “file://parent-stack.yaml“ points to your parent stack template file, and ParameterKey=NestedStackParameter,ParameterValue=Value specifies the parameter values to be passed to the nested stack.

Conclusion

Nested stacks in AWS CloudFormation provide a powerful way to manage and configure codedriven processes. By dividing the structure into smaller parts, you can achieve better modularity, reusability, and sustainability. As with any tool, it’s important to understand its intricacies and best practices to get the most out of it.

Drop a query if you have any questions regarding AWS CloudFormation and we will get back to you quickly.

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