Cannot find module (AWS Lambda Error) [Solved]

# Table of Contents

# Cannot find module (AWS Lambda Error) [Solved]

The "Cannot find module" occurs when a Lambda function is trying to access a module which is not available in the function's execution runtime.

The most common causes for the error are:

zipping the wrong files, e.g. zipping a directory instead of the contents of the directory. AWS Lambda expects to extract the zip file and find your handler, not a directory with your handler in it.
having a wrong folder structure when using layers. There is a language-specific folder structure you have to follow when using Lambda layers, e.g. nodejs/node_modules for Node.js layers.

This article shows how to solve the error:

When importing modules in a Lambda directly, without layers.
When importing modules in a Lambda function, using layers.

The code for this article is available on GitHub

To solve the "Cannot find module" error when importing modules directly to a Lambda function:

Have the following folder structure:

shell

Copied!
index.js
package.json
node_modules
    your_npm_modules

View the example on Github. The code is in the without-layers directory.

I initialized a package.json file and installed a 3rd party module in the directory of my lambda function's index.js file.

without-layers

Copied!
npm init -y

npm install date-fns@2.24.0

The code in the index.js file imports and uses the module.

The code for this article is available on GitHub

without-layers/index.js

Copied!
// 👇️ import third party module
const {format} = require('date-fns');

exports.handler = async event => {
  return {
    statusCode: 200,
    body: JSON.stringify({
      today: format(new Date(), "👉️ 'Today is a' eeee"),
    }),
  };
};

Open your terminal in the directory where the index.js file and node_modules directory are located. In this case, the without-layers directory, and zip the contents of the directory

without-layers

Copied!
zip -r9 lambda.zip .

Note that we are zipping the contents of the directory, and not the directory itself. Once the Lambda service extracts the zip file, it will find our index.js file and the node_modules directory where our third-party module is.

Update the Lambda function's code by uploading the lambda.zip file. Open your terminal in the directory where the lambda.zip file is and run the update-function-code command:

without-layers

Copied!
aws lambda update-function-code --function-name YOUR_LAMBDA --zip-file fileb://lambda.zip

update function code

Verify that the Lambda function's handler is set to index.handler (an index.js file exporting a handler function):

verify handler configured correctly

Finally, invoke the function and verify that it can access the third-party module.

verify module found

Now Lambda is able to find the third-party module because we've zipped the contents of our index.js file alongside the node_modules directory.

# Solve Cannot find Module Lambda Error when using Layers

To solve the "Cannot find module" error when importing modules using Lambda layers:

Have the following folder structure:

The code for this article is available on GitHub

with-layers

Copied!
index.js
layers
  date-fns
    nodejs
      package.json
      node_modules

You can view the folder structure in the with-layers directory in the example repository.

Note that the nodejs/node_modules folder structure is what Lambda expects when working with layers in Node.js.

with layers folder structure

Open your terminal in the layers/date-fns/nodejs directory and install your third-party packages:

layers/date-fns/nodejs

Copied!
npm init -y

npm install date-fns@2.24.0

The code for the index.js file looks as follows:

The code for this article is available on GitHub

index.js

Copied!
// 👇️ import third party package
const {format} = require('date-fns');

exports.handler = async event => {
  return {
    statusCode: 200,
    body: JSON.stringify({
      today: format(new Date(), "👉️ 'Today is a' eeee"),
    }),
  };
};

Open your terminal in the layers/date-fns directory and zip the contents.

When the zip is extracted, the nodejs/node_modules folder structure has to be directly accessible.

layers/date-fns

Copied!
# in the layers/date-fns directory

zip -r9 date-fns-layer.zip .

To create or update the Lambda layer, open your terminal in the layers/date-fns directory and run the publish-layer-version command:

layers/date-fns

Copied!
aws lambda publish-layer-version --layer-name date-fns-layer --description "add date-fns library" --zip-file fileb://date-fns-layer.zip --compatible-runtimes nodejs10.x nodejs12.x nodejs14.x

create layer

Attach the layer to the Lambda function. The easiest way to add a layer to a function is using the AWS Lambda console.

In the Code tab, scroll down to the Layers section and click Add a layer.

add a layer

Select Custom layers and pick your layer from the dropdown menu. Selecting the latest version and click Add.

select your layer

The last step is to update the code of the Lambda function. In this case the index.js file looks as follows:

The code for this article is available on GitHub

index.js

Copied!
// 👇️ import third party package
const {format} = require('date-fns');

exports.handler = async event => {
  return {
    statusCode: 200,
    body: JSON.stringify({
      today: format(new Date(), "👉️ 'Today is a' eeee"),
    }),
  };
};

Open your terminal in the directory where the index.js file is located and zip its contents:

Note that we are zipping the index.js file, not the folder that contains it.

with-layers

Copied!
zip -r9 lambda.zip index.js

zip lambda code

To update the function's code, open your terminal in the directory where the lambda.zip file is and run the update-lambda-code command:

shell

Copied!
aws lambda update-function-code --function-name YOUR_LAMBDA --zip-file fileb://lambda.zip

update lambda code

Verify that the Lambda function's handler is set to index.handler (an index.js file exporting a handler function):

verify handler configured correctly

Finally, invoke the function and verify that it can access the third-party module.

verify module found

Now lambda is able to find the third-party module because we used the expected directory format for Node.js Lambda layers - nodejs/node_modules.

I've also written a detailed guide on how to use npm modules in AWS Lambda.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.

You can use the search field on my Home Page to filter through all of my articles.

Cannot find module (AWS Lambda Error) [Solved]

# Table of Contents