Custom resources

As discussed previously in this chapter, it's common for there to be a lengthy wait between the release of a new AWS feature and your ability to use that feature in CloudFormation.

Before custom resources, this led AWS developers down the path of doing over 95 percent of their automation in CloudFormation and then running some CLI commands to fill in the gaps. It was often difficult to tell exactly which resources belonged to which stack, and knowing exactly when your stack had finished execution became a guessing game.

Fast forward to today, and the emerging pattern is to use a custom resource to delegate to a AWS Lambda function. Lambda can fill in the gaps by making API calls on your behalf, and it becomes much easier to track the heritage and completion of these resources.

With any luck, you won't need to use this feature for a while. In the meantime, the AWS custom resource documentation is quite comprehensive. If you are trying to use CloudFormation to create a resource that you can't find in the AWS docs, then it's likely that it's not supported in CloudFormation yet and using custom resources is your answer. For more information, refer to http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-custom-resources.html.

Table of Contents for Custom resources

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Table of Contents for
Custom resources