cdk-custom-resource-construct-example
v1.2.315
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This is an updated example of how to create a Custom Resource Construct for CDK. This example will walk you through the process of creating a [CDK Construct](https://constructs.dev/) that uses Typescript Custom Resources.
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CDK Custom Resource Construct Example
This is an updated example of how to create a Custom Resource Construct for CDK. This example will walk you through the process of creating a CDK Construct that uses Typescript Custom Resources.
Custom Resources
Custom Resources allow you to deploy and invoke Lambda functions during the deployment of a CDK. This can be used to supplement CDKs with features that are not natively part of CloudFormation or CDK.
In this example, our Lambda function is simply multiplying an input and returning the result
try {
const multiplyResult = event.ResourceProperties.customResourceNumber * 2;
response.Status = 'SUCCESS';
response.Data = { Result: multiplyResult };
return response;
} catch (error) {
if (error instanceof Error) {
response.Reason = error.message;
}
response.Status = 'FAILED';
response.Data = { Result: error };
return response;
}
Bundling
Because we are using Typescript for our Lambda, we must transpile it before we use it. To do this, we will use projen to execute an esbuild
on our Lambda source code during the build.
To do this, in the .projenrc.ts
we use bundler.addBundle
:
project.bundler.addBundle('./resources/lambda/', {
platform: 'node',
target: 'node18',
});
This will create an index.js
in the assets/resources/lambda
directory. This is the what we will use in the Custom Resource.
Custom Resource Provider
To create the Custom Resource we will use CustomResourceProvider
. This is different from Provider
which is what is normally used within a CDK.
const customResourceProvider = CustomResourceProvider.getOrCreateProvider(
this,
'Custom::Resource',
{
codeDirectory:
'node_modules/cdk-custom-resource-construct-example/assets/resources/lambda',
runtime: CustomResourceProviderRuntime.NODEJS_18_X,
timeout: Duration.seconds(60),
policyStatements: [
{
Effect: 'Allow',
Action: [
'logs:CreateLogGroup',
'logs:CreateLogStream',
'logs:PutLogEvents',
],
Resource: '*',
},
],
},
);
By using []getOrCreateProvider
](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.CustomResourceProvider.html#static-getwbrorwbrcreatewbrproviderscope-uniqueid-props) we can ensure that the Lambda function is created only once even if it used multiple times. The codeDirectory
used here is the output directory of the bundling. This is what will be used in the CDK that uses this Construct.
Custom Resource
Finally, we will create the Custom Resource using the previously created Provider.
const customResourceResult = new CustomResource(this, 'customResourceResult', {
serviceToken: customResourceProvider.serviceToken,
properties: {
customResourceNumber: props.customResourceNumber,
},
});
this.customResourceResult = customResourceResult.getAttString('Result');
This Custom Resource will take a prop
when called and return the result.
Using the Custom Resource
To use this Construct, we will import the CustomResourceExample
, implement it, and pass it a prop.
import { CfnOutput, Stack, StackProps } from 'aws-cdk-lib';
import { Construct } from 'constructs';
import { CustomResourceExample } from 'cdk-custom-resource-construct-example';
export class CdkCustomResourceConstructDemoStack extends Stack {
constructor(scope: Construct, id: string, props?: StackProps) {
super(scope, id, props);
const result = new CustomResourceExample(this, 'customResourceResult', {
customResourceNumber: 5,
});
new CfnOutput(this, 'customResourceOutput', {
value: result.customResourceResult,
});
}
}
When used this way, the Custom Resource will deploy the Lambda, invoke it, and return the result to the calling CDK.
Developing
It can be difficult to develop and test a Construct. yalc
is a tool that can help with this by allowing us to "publish" locally. To use yalc
, it should be installed as a devDep
in the .projenrc.ts
of the source Construct.
devDeps: ['yalc', 'esbuild'],
After building the construct using yarn projen build
, you can use yalc publish --push --sig
to push this package to the local store. This should result in an output similar to:
[email protected]+80079907 published in store.
By adding --sig
we can differentiate versions. In this example +80079907
is the sig.
Next, you can create a project that uses this package. To do this, you can add the package with yalc: yalc add cdk-custom-resource-construct-example
. This will add the package to the package.json
file that can be used like any other package. If needed, you can use yalc update
. The output should be similar to:
Package [email protected]+80079907 added