AWS DevOps Blog

Import entire applications into AWS CloudFormation

AWS Infrastructure as Code (IaC) enables customers to manage, model, and provision infrastructure at scale. You can declare your infrastructure as code in YAML or JSON by using AWS CloudFormation, in a general purpose programming language using the AWS Cloud Development Kit (CDK), or visually using Application Composer. IaC configurations can then be audited and version controlled in a version control system of your choice. Finally, deploying AWS IaC enables deployment previews using change sets, automated rollbacks, proactive enforcement of resource compliance using hooks, and more. Millions of customers enjoy the safety and reliability of AWS IaC products.

Not every resource starts in IaC, however. Customers create non-IaC resources for various reasons: they didn’t know about IaC, or they prefer to work in the CLI or management console. In 2019, we introduced the ability to import existing resources into CloudFormation. While this feature proved integral for bringing resources into IaC on an individual basis, the process of manually creating templates to match those resources wasn’t ideal. Customers were required to look up documentation on resources and painstakingly copy values manually. Customers also told us they traditionally engaged with applications (that is, groupings of related resources), so dealing with individual resources didn’t match that experience. We set out to create a more holistic flow for managing resources and their relations.

Recently, we announced the IaC generator and CDK Migrate, an end-to-end experience that enables customers to create an IaC configuration based off a resource as well as its relationships. This works by scanning an AWS account and using the CloudFormation resource type schema to find relationships between resources. Once this configuration is created, you can use it to either import those resources into an existing stack, or create a brand new stack from scratch. It’s now possible to bring entire applications into a managed CloudFormation stack without having to recreate any resources!

In this post, I’ll explore a common use case we’ve seen and expect the IaC generator to solve: an existing network architecture, created outside of any IaC tool, needs to be managed by CloudFormation.

IaC generator in Action

Consider the following scenario:

As a new hire to an organization that’s just starting its cloud adoption journey, you’ve been tasked with continuing the development of the team’s shared Amazon Virtual Private Cloud (VPC) resources. These are actively in use by the development teams. As you dig around, you find out that these resources were created without any form of IaC. There’s no documentation, and the person who set it up is no longer with the team. Confounding the problem, you have multiple VPCs and their related resources, such subnets, route tables, and internet gateways.

You understand the benefits of IaC – repeatability, reliability, auditability, and safety. Bringing these resources under CloudFormation management will extend these benefits to your existing resources. You’ve imported resources into CloudFormation before, so you set about the task of finding all related resources manually to create a template. You quickly discover, however, that this won’t be a simple task. VPCs don’t store relations to items; instead, relations are reversed – items know which VPC they belong to, but VPCs don’t know which items belong to them. In order to find all the resources that are related to a VPC, you’ll have to manually go through all the VPC-related resources and scan to see which vpc-id they belong to. You’ll have to be diligent, as it’s very easy to miss a resource because you weren’t aware that it existed or it may even be different class of resource altogether! For example, some resources may use an elastic network interface (ENI) to attach to the VPC, like an Amazon Relational Database Service instance.

You, however, recently learned about the IaC generator. The generator works by running a scan of your account and creating an up-to-date inventory of resources. CloudFormation will then leverage the resource type schema to find relationships between resources. For example, it can determine that a subnet has a relationship to a VPC via a vpc-id property. Once these relationships have been determined, you can then select the top-level resources you want to generate a template for. Finally, you’ll be able to leverage the wizard to create a stack from this existing template.

You can navigate to the IaC generator page in the Amazon Management Console and start a scan on your account. Scans last for 30 days, and you can run three scans per day in an account.

Scan account button and status

Once the scan completes, you create a template by selecting the Create Template button. After selecting Start from a new template, you fill out the relevant details about the stack, including the Template name and any stack policies. In this case, you leave it as Retain.

Create template section with "Start from a new template" selected

On the next page, you’ll see all the scanned resources. You can add filters to the resource such as tags to view a subset of scanned resources. This example will only use a Resource type prefix filter. More information on filters can be found here. Once you find the VPC, you can select it from the list.

A VPC selected in the scanned resources list]

On the next page, you’ll see the list of resources that CloudFormation has determined to have a link to this VPC. You see this includes a myriad of networking related resource. You keep these all selected to create a template from them.

A list of related resources, all selected

At this point, you select Create template and CloudFormation will generate a template from the existing resources. Since you don’t have an existing stack to import these resource into, you must create a new stack. You now select this template and then select the Import to stack button.

The template detail page with an import to stack button

After entering the Stack name, you can then enter any Parameters your template needs.

The specify stack details page, with a stack name of "networking" entered

CloudFormation will create a change set for your new stack. Change sets allow you to see the changes CloudFormation will apply to a stack. In this example, all of the resources will have the Import status. You see the resources CloudFormation found, and once you’re satisfied, you create the stack.

A change set indicating the previously found resources will be created

At this point, the create stack operation will proceed as normal, going through each resource and importing it into the stack. You can report back to your team that you have successfully imported your entire networking stack! As next steps, you should source this template in a version control system. We recently announced a new feature to keep CloudFormation templates synced with popular version control systems. Finally, make sure to make any changes through CloudFormation to avoid a configuration drift between the stated configuration and the existing configuration.

This example was primarily CloudFormation-based, but CDK customers can use CDK Migrate to import this configuration into a CDK application.

Available Now

The IaC generator is now available in all regions where CloudFormation is supported. You can access the IaC generator using the console, CLI, and SDK.


In this post, we explored the new IaC generator feature of CloudFormation. We walked through a scenario of needing to manage previously existing resources and using the IaC generator’s provided wizard flow to generate a CloudFormation template. We then used that template and created a stack to manage these resources. These resources will now enjoy the safety and repeatability that IaC provides. Though this is just one example, we foresee other use cases for this feature, such as enabling a console-first development experience. We’re really excited to hear your thoughts about the feature. Please let us know how you feel!

About the author

Dan Blanco

Dan is a senior AWS Developer Advocate based in Atlanta for the AWS IaC team. When he’s not advocating for IaC tools, you can either find him in the kitchen whipping up something delicious or flying in the Georgia sky. Find him on twitter (@TheDanBlanco) or in the AWS CloudFormation Discord.