Node.js layer: "Cannot redefine property: handler" when using esbuild

[smagura-jm]

Describe the bug
The Node.js layer is working correctly when using a handwritten CommonJS handler like this:

module.exports = {
  handler: () => 200
}

My real code is written in ES Modules and is bundled via esbuild. Compile the following code with esbuild and then deploy it to Lambda.

export const handler = () => 200;

Now, the Lambda fails with the error

{
  "errorType": "TypeError",
  "errorMessage": "Cannot redefine property: handler",
  "stack": [
    "TypeError: Cannot redefine property: handler",
    "    at Function.defineProperty (<anonymous>)",
    "    at n (/opt/wrapper.js:1:242970)",
    "    at i (/opt/wrapper.js:1:243369)",
    "    at o._wrap (/opt/wrapper.js:1:252372)",
    "    at x.patch (/opt/wrapper.js:1:204436)",
    "    at /opt/wrapper.js:1:254659",
    "    at Array.reduce (<anonymous>)",
    "    at t._onRequire (/opt/wrapper.js:1:254445)",
    "    at t (/opt/wrapper.js:1:255685)",
    "    at Module.T (/opt/wrapper.js:1:92076)"
  ]
}

Steps to reproduce

1. Clone the opentelemetry-lambda repo and execute npm run build in the nodejs directory. This produces a layer.zip file.
2. Upload layer.zip as a layer via the AWS Console.
3. Create a new Lambda function (Node.js 22.x) and add the layer to it.
4. In the environment variables for the Lambda, set AWS_LAMBDA_EXEC_WRAPPER to /opt/otel-handler.
5. Locally, create index.js as

   export const handler = () => 200;

6. Bundle the code using esbuild by running npx esbuild index.js --platform=node --bundle --outfile=compiled.js. View the compiled bundle here
7. Paste the compiled code into the code editor for the Lambda function in the AWS Console. Click "Deploy".
8. In the AWS Console, test the Lambda function with an arbitrary payload.

What did you expect to see?
The Lambda succeeds.

What did you see instead?
The Lambda fails with the error

{
  "errorType": "TypeError",
  "errorMessage": "Cannot redefine property: handler",
  "stack": [
    "TypeError: Cannot redefine property: handler",
    "    at Function.defineProperty (<anonymous>)",
    "    at n (/opt/wrapper.js:1:242970)",
    "    at i (/opt/wrapper.js:1:243369)",
    "    at o._wrap (/opt/wrapper.js:1:252372)",
    "    at x.patch (/opt/wrapper.js:1:204436)",
    "    at /opt/wrapper.js:1:254659",
    "    at Array.reduce (<anonymous>)",
    "    at t._onRequire (/opt/wrapper.js:1:254445)",
    "    at t (/opt/wrapper.js:1:255685)",
    "    at Module.T (/opt/wrapper.js:1:92076)"
  ]
}

What version of collector/language SDK version did you use?
I cloned the opentelemetry-lambda repo, and the latest commit on main was 939cecd.

What language layer did you use?
Node.js

[serkan-ozal]

Hi @smagura-jm,

Unfortunately, this is the limitation of the shimmer which is the library OTEL JS SDK uses for monkey patching to instrument user handler. esbuild generate immutable objects which are not writeable and this is the point where shimmer fails.

Here are related issues and their discussions:

• Cannot redefine property: handle when run as AWS lambda evanw/esbuild#2199
• [Bug] Issue using aws-otel-nodejs in Lambda aws-observability/aws-otel-lambda#99
• crash when using aws-lambda instrumentation opentelemetry-js#2193
• https://dev.to/heymarkkop/how-to-solve-cannot-redefine-property-handler-on-aws-lambda-3j67

So, the only solution (workaround) I see is converting your handler

from

export const handler = () => 200;

to

const handler = () => 200;

module.exports = { handler }

[smagura-jm]

Thanks for your answer! It's unfortunate that it doesn't work without the workaround. Closing the issue.

[serkan-ozal]

Thanks @smagura-jm.

Did it work?

const handler = () => 200;

module.exports = { handler }

[smagura-jm]

Yes, that worked.

I was actually able to get this to work in my real codebase by converting my handler files to CommonJS modules. My code is still able to use the import syntax, even though it is CommonJS (I did not realize that was possible). All of my non-handler files are still in ES Modules.

Thanks!