Runtime.ImportModuleError: Error: Cannot find module 'lodash'

What it means

Lambda runs your function in two phases, and this error belongs entirely to the first one. During init, the runtime loads your handler file and everything it imports, top to bottom, before any event arrives. During invoke, it calls the handler with the event. A module that cannot be resolved fails in init, which means the failure happens before your code has run a single line and before there is an event to fail.

That timing explains the two things people find most confusing about it. The first is that the logs contain none of your own output — not even a log line at the very top of the file, because the file never finished loading. The second is that it fails identically every single time. A bug in your handler might affect one request in a thousand; a missing module affects every invocation on every container, forever, until the package changes.

The Require stack: block is the part worth reading and the part most often skipped. It is the chain of files Node walked to reach the failed require, listed innermost first. When the missing module is one you have never heard of, that chain tells you which of your dependencies wanted it — which is usually a package whose own dependencies did not make it into the bundle, rather than anything you imported yourself.

Almost every instance of this error comes down to a difference between the machine that built the package and the machine that runs it. Case sensitivity differs between macOS and Linux. devDependencies are present locally and pruned in CI. Native bindings are compiled for arm64 on a laptop and loaded on x86_64 in production. The AWS SDK is present in the runtime in one major version and absent in another. In every case the code is correct and the artifact is wrong, which is why the fix is nearly always in the build rather than in the source.

What it looks like in CloudWatch

This is the shape the failure arrives in: the lines of one invocation scattered among everything else the log group received at the same moment.

The panel on the right is generated by running the excerpt on the left through the same parser that powers the free web stitcher — it is what the tool actually produces for this input, not an illustration of it.

How to confirm it from the logs

Three things identify this precisely. The error appears immediately after INIT_START and before any of your own logging, because it happens during module load. The Require stack: block underneath lists the chain of files that led to the failed require, and its first entry names the file that actually asked for the module. And the REPORT line carries Error Type: Runtime.ImportModuleError on runtimes that write it.

The name in quotes is the module Node could not resolve, not necessarily the one you are missing — a package present in your bundle can still fail if one of its dependencies is absent. Read the Require stack to see which of your files started the chain.

Causes, most likely first

Fixes

bash# What did we actually ship?
aws lambda get-function --function-name my-function \
  --query 'Code.Location' --output text | xargs curl -s -o /tmp/fn.zip

unzip -l /tmp/fn.zip | grep -i 'node_modules/lodash'

bashnpm ci --omit=dev \
  --os=linux --cpu=x64 \
  --foreground-scripts

zip -qr function.zip index.js node_modules package.json

bashnpx esbuild src/index.js \
  --bundle \
  --platform=node \
  --target=node22 \
  --outfile=dist/index.js

js// v2 — not present on Node 18+
// const AWS = require("aws-sdk");
// const s3 = new AWS.S3();

// v3 — available in the runtime
import { S3Client, GetObjectCommand } from "@aws-sdk/client-s3";
const s3 = new S3Client({});

Also seen as

The same underlying failure, worded differently by a different runtime, SDK version, or logging layer. All of these land here — there is no separate page for each phrasing.

Related errors

Errors that show up alongside this one, or that people mistake for it.

References

• AWS Lambda Developer Guide — Troubleshoot deployment issues
• AWS Lambda Developer Guide — Deploy Node.js Lambda functions with .zip archives