Serverless - Lambda Layers "Cannot find module 'request'" - aws-lambda

Question

When I deploy my serverless api using:
serverless deploy
The lambda layer gets created but when I go to run the function is gives me this error:
"Cannot find module 'request'"
But if I upload the .zip file manually through the console (the exactly same file thats uploaded when I deploy), it works fine.
Any one have any idea why this is happening?
environment:
SLS_DEBUG: "*"
provider:
name: aws
runtime: nodejs8.10
stage: ${opt:api-type, 'uat'}-${opt:api, 'payment'}
region: ca-central-1
timeout: 30
memorySize: 128
role: ${file(config/prod.env.json):ROLE}
vpc:
securityGroupIds:
- ${file(config/prod.env.json):SECURITY_GROUP}
subnetIds:
- ${file(config/prod.env.json):SUBNET}
apiGateway:
apiKeySourceType: HEADER
apiKeys:
- ${file(config/${opt:api-type, 'uat'}.env.json):${opt:api, "payment"}-APIKEY}
functions:
- '${file(src/handlers/${opt:api, "payment"}.serverless.yml)}'
package:
# individually: true
exclude:
- node_modules/**
- nodejs/**
plugins:
- serverless-offline
- serverless-plugin-warmup
- serverless-content-encoding
custom:
contentEncoding:
minimumCompressionSize: 0 # Minimum body size required for compression in bytes
layers:
nodejs:
package:
artifact: nodejs.zip
compatibleRuntimes:
- nodejs8.10
allowedAccounts:
- "*"
Thats what my serverless yaml script looks like.

Answer 1

I was having a similar error to you while using the explicit layers keys that you are using to define a lambda layer.
My error (for the sake of web searches) was this:
Runtime.ImportModuleError: Error: Cannot find module <package name>
I feel this is a temporary solution b/c I wanted to explicitly define my layers like you were doing, but it wasn't working so it seemed like a bug.
I created a bug report in Serverless for this issue. If anyone else is having this same issue they can track it there.
SOLUTION
I followed this this post in the Serverless forums based on these docs from AWS.
I zipped up my node_modules under the folder nodejs so it looks like this when it is unzipped nodejs/node_modules/<various packages>.
Then instead of using the explicit definition of layers I used the package and artifact keys like so:
layers:
test:
package:
artifact: test.zip
In the function layer it is referred to like this:
functions:
function1:
handler: index.handler
layers:
- { Ref: TestLambdaLayer }
The TestLambdaLayer is a convention of <your name of layer>LambdaLayer as documented here

Answer 2

Make sure you run npm install inside your layers before deploying, ie:
cd ~/repos/repo-name/layers/utilityLayer/nodejs && npm install
Otherwise your layers will get deployed without a node_modules folder. You can download the .zip of your layer from the Lambda UI to confirm the contents of that layer.

Answer 3

If anyone face a similar issue Runtime.ImportModuleError, is fair to say that another cause of this issue could be a package exclude statement in the serverless.yml file.
Be aware that if you have this statement:
package:
exclude:
- './**'
- '!node_modules/**'
- '!dist/**'
- '.git/**'
It will cause exactly the same error, on runtime once you've deployed your lambda function (with serverless framework). Just, ensure to remove the ones that could create a conflict across your dependencies

Answer 4

I am using typescript with the serverless-plugin-typescript and I was having a same error, too.
When I switched from
const myModule = require('./src/myModule');
to
import myModule from './src/myModule';
the error disappeared. It seems like the files were not included into the zip file by serverless when I was using require.
PS: Removing the serverless-plugin-typescript and switching back to javascript also solved the problem.