Cannot find module 'handler' when running simple lambda deployed by serverless

Question

I am trying to start learning serverless / lambda so I created a simple lambda and deployed it with serverless which worked.

However when I want to test the endpoint of the lampbda I get a 502 back. When I look in the logs it tells me that it can not find the module handler which does not make any sense...

here is the log:

{
"errorType": "Runtime.ImportModuleError",
"errorMessage": "Error: Cannot find module 'handler'\nRequire stack:\n- 
/var/runtime/UserFunction.js\n- /var/runtime/index.js",
 "trace": [
    "Runtime.ImportModuleError: Error: Cannot find module 'handler'",
"Require stack:",
"- /var/runtime/UserFunction.js",
"- /var/runtime/index.js",
"    at _loadUserApp (/var/runtime/UserFunction.js:100:13)",
"    at Object.module.exports.load (/var/runtime/UserFunction.js:140:17)",
"    at Object.<anonymous> (/var/runtime/index.js:43:30)",
"    at Module._compile (internal/modules/cjs/loader.js:1158:30)",
"    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1178:10)",
"    at Module.load (internal/modules/cjs/loader.js:1002:32)",
"    at Function.Module._load (internal/modules/cjs/loader.js:901:14)",
"    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)",
"    at internal/main/run_main_module.js:18:47"
]
}

dege · Accepted Answer · 2020-04-25 21:25:07Z

7

This normally means that it can not find the method that is the starting point to execute.

For example on your serverless.yml you can have something like this

functions:
  getUsers:
    handler: userFile.handler

this would mean that it's required to have a userFile in the same folder of the serverless.yml with the method handler exported.

module.exports.hello = async event => {
  return {
    statusCode: 200,
    body: JSON.stringify(
      {
        message: 'Go Serverless v1.0! Your function executed successfully!',
        input: event,
      },
      null,
      2
    ),
  };
};

Note that it does not need to be named handler function, just needs to have the same name defined on the serverless.yml

answered Apr 25, 2020 at 21:25

dege

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2 Comments

zlZimon Over a year ago

yep that was the problem, the serverless.yml was not in the same folder. Thanks!

ROKIKOKI Over a year ago

Also you may have the same problem if your handler file is named like 'user.controller' and if your try to access it in your serverless.yml file handler: user.controller.hello

Jasper Desmet · Accepted Answer · 2022-03-10 14:01:06Z

1

I ran into the same error when launching a lambda locally using AWS sam, with Webstorm.

Turns out a previous run had not correctly stopped and destroyed the docker container running the lambda. Stopping and removing said docker container fixed the problem for me.

answered Mar 10, 2022 at 14:01

Jasper Desmet

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