In order to import an existing Lambda function in AWS CDK, we have to use the static `fromFunctionArn` method on the `Function` class.

Import an Existing Lambda Function in AWS CDK


## Importing an Existing Lambda Function in AWS CDK

**In order to import an existing lambda function in CDK, we have to use the
static
[fromFunctionArn](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-lambda.Function.html#static-fromwbrfunctionwbrarnscope-id-functionarn)
method on the
[Function](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-lambda.Function.html#class-function-construct)
class.**

<GithubRepo repoName="aws-cdk-import-existing-lambda" />

Let's look at a simple example where we import a lambda function and use it in
an API Gateway resource:

```typescript:lib/cdk-starter-stack.ts
import * as apigateway from '@aws-cdk/aws-apigateway';
import * as lambda from '@aws-cdk/aws-lambda';
import * as cdk from '@aws-cdk/core';

export class CdkStarterStack extends cdk.Stack {
  constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    // 👇 import existing Lambda by ARN
    const importedLambdaFromArn = lambda.Function.fromFunctionArn(
      this,
      'external-lambda-from-arn',
      `arn:aws:lambda:${cdk.Stack.of(this).region}:${
        cdk.Stack.of(this).account
      }:function:YOUR_FUNCTION_NAME`,
    );

    console.log('functionArn 👉', importedLambdaFromArn.functionArn);
    console.log('functionName 👉', importedLambdaFromArn.functionName);

    // 👇 create API
    const api = new apigateway.RestApi(this, 'api');

    // 👇 add a /test route on the API
    const test = api.root.addResource('test');

    // 👇 integrate imported Lambda at GET /test on the API
    test.addMethod(
      'GET',
      new apigateway.LambdaIntegration(importedLambdaFromArn),
    );
  }
}
```

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Let's go over what we did in the code snippet.

1. we imported an existing lambda function in our CDK stack, using the static
   `fromFunctionArn` method. The method takes 3 parameters:
   - `scope` - the construct scope
   - `id` - an identifier for the resource, must be unique within the scope
   - `functionArn` - the ARN of the function we want to import
2. we created an API Gateway and integrated the imported lambda function to
   serve requests for http GET at the `/test` route

<Alert>
  The function ARN can be passed to the CDK stack as a secret from secrets
  manager, environment variable, CDK context, or a parameter.
</Alert>

If the function you're trying to import is in the same environment (`account`
and `region`) as the CDK stack, you can use the stack values to create most of
the function ARN, all you need to add is the function name.

```bash:lambda-arn-format
arn:aws:lambda:LAMBDA_REGION:LAMBDA_ACCOUNT:function:LAMBDA_NAME
```

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If I deploy the CDK stack with the `npx cdk deploy` command, I can see that the
imported Lambda has been integrated with the API at the `/test` route:

![imported lambda integrated](/images/blog/aws-cdk-import-existing-lambda/imported-lambda-integrated.webp)

## Further Reading

- [Write TypeScript Lambda functions in AWS CDK - Complete Guide](/blog/aws-cdk-typescript-lambda)
- [AWS CDK Tutorial for Beginners - Step-by-Step Guide](/blog/aws-cdk-tutorial-typescript)
- [What is a Token in AWS CDK](/blog/what-is-aws-cdk-token)
- [CDK Constructs - Complete Guide](/blog/cdk-constructs-tutorial)
- [What is an identifier (id) in AWS CDK](/blog/aws-cdk-identifiers)
- [How to use Context in AWS CDK](/blog/how-to-use-context-aws-cdk)
- [How to use Parameters in AWS CDK](/blog/aws-cdk-parameters-example)

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Import an Existing Lambda Function in AWS CDK

Importing an Existing Lambda Function in AWS CDK #

Further Reading #

Borislav Hadzhiev

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Import an Existing Lambda Function in AWS CDK

Importing an Existing Lambda Function in AWS CDK #

Further Reading #

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