AWS CloudFormation Construct Library
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This is a developer preview (public beta) module. Releases might lack important features and might have
future breaking changes.
This module is part of the AWS Cloud Development Kit project.
Custom Resources
Custom Resources are CloudFormation resources that are implemented by
arbitrary user code. They can do arbitrary lookups or modifications
during a CloudFormation synthesis run.
You will typically use Lambda to implement a Construct implemented as a
Custom Resource (though SNS topics can be used as well). Your Lambda function
will be sent a CREATE
, UPDATE
or DELETE
message, depending on the
CloudFormation life cycle, and can return any number of output values which
will be available as attributes of your Construct. In turn, those can
be used as input to other Constructs in your model.
In general, consumers of your Construct will not need to care whether
it is implemented in term of other CloudFormation resources or as a
custom resource.
Note: when implementing your Custom Resource using a Lambda, use
a SingletonLambda
so that even if your custom resource is instantiated
multiple times, the Lambda will only get uploaded once.
Example
Sample of a Custom Resource that copies files into an S3 bucket during deployment
(implementation of actual copy.py
operation elided).
interface CopyOperationProps {
sourceBucket: IBucket;
targetBucket: IBucket;
}
class CopyOperation extends Construct {
constructor(parent: Construct, name: string, props: DemoResourceProps) {
super(parent, name);
const lambdaProvider = new SingletonLambda(this, 'Provider', {
uuid: 'f7d4f730-4ee1-11e8-9c2d-fa7ae01bbebc',
code: new LambdaInlineCode(resources['copy.py']),
handler: 'index.handler',
timeout: 60,
runtime: LambdaRuntime.Python3,
});
new CustomResource(this, 'Resource', {
provider: CustomResourceProvider.lambda(provider),
properties: {
sourceBucketArn: props.sourceBucket.bucketArn,
targetBucketArn: props.targetBucket.bucketArn,
}
});
}
}
More examples are in the example
directory, including an example of how to use
the cfnresponse
module that is provided for you by CloudFormation.
References
See the following section of the docs on details to write Custom Resources: