Using the CfnOutput created inside a LambdaRestApi in AWS CDK

Question

I'm creating a LambdaRestApi as follows

        this.gateway = new apigw.LambdaRestApi(this, "Endpoint", {
            handler: hello,
            endpointExportName: "MainURL"
        })

and I'd like to get to the CfnOutput it generates, is it possible? I want to pass it to other functions and I want to avoid creating a new one.

Answer 1

Assuming you are using the following code for your LambdaRestApi:

this.gateway = new apigw.LambdaRestApi(this, "Endpoint", {
    handler: hello,
    endpointExportName: "MainURL"
});

Referencing in same stack as LambdaRestApi

const outputValue = this.gateway.urlForPath("/");

Looking at the source code , the output value is just a call to urlForPath. The method is public, so you can use it directly.

Referencing from another stack

You can use cross stack references to get a reference to the output value of the stack.

import { Fn } from 'aws-cdk-lib';
const outputValue = Fn.importValue("MainURL");

If you try to use the first method in another stack, CDK will just generate a cross stack reference dynamically by adding extra outputs, so it is better to import the value directly.

Answer 2

I'd like to get to the CfnOutput it generates, is it possible?

Yes. Use the escape hatch syntax to get a reference to the CfnOutput that RestApi creates for the endpointExportName :

const urlCfnOutput = this.gateway.node.findChild('Endpoint') as cdk.CfnOutput;

console.log(urlCfnOutput.exportName);
// MainURL

console.log(urlCfnOutput.value);
// https://${Token[TOKEN.258]}.execute-api.us-east-1.${Token[AWS.URLSuffix.3]}/${Token[TOKEN.277]}/

Prefer standard CDK

As their name suggests, "escape hatches" are for "emergencies" when the CDK's standard solutions fail. Your use case may be one such instance, I don't know. But as @Kaustubh Khavnekar points out, you don't need the CfnOutput to get the url token value.

console.log(this.gateway.url)
// https://${Token[TOKEN.258]}.execute-api.us-east-1.${Token[AWS.URLSuffix.3]}/${Token[TOKEN.277]}/