Docker agent inside Jenkins - npm "cannot find module" - node.js

Question

I'm working on automation of following build steps:
- building frontend application with webpack
- running tests on it
I am using Jenkins with blue-ocean plugin enabled, here is Jenkinsfile:
Jenkinsfile:pipeline {
agent {
dockerfile {
filename 'Dockerfile'
}
}
stages {
stage('Build') {
steps {
sh 'npm run build'
}
}
}
}
I'm using following Dockerfile
FROM node:latest
WORKDIR /app
COPY . /app
RUN npm install webpack -g && npm install
The problem is that when running npm run build it can not find webpack:
> webpack --config webpack-production.config.js --progress --colors
module.js:529
throw err;
^
Error: Cannot find module 'webpack'
at Function.Module._resolveFilename (module.js:527:15)
at Function.Module._load (module.js:476:23)
at Module.require (module.js:568:17)
at require (internal/module.js:11:18)
at Object.<anonymous> (/var/lib/jenkins/workspace/l-ui-webpack-example_master-IXSLD4CQSVAM2DRFHYHOYUANEHJ73R5PUGW4BMYVT5WPGB6ZZKEQ/webpack-production.config.js:1:79)
It looks like commands are being executed in host context, not on container as manual running works just fine:
docker build . -t sample
docker run sample npm run build
Here is full jenkins log:Jenkins build log
Here is a link to a repository: Source code

Answer 1

I had exactly the same issue. For some reason, 'RUN npm install' within the Dockerfile didn't take effect in the Jenkins pipeline although it worked well when I built the image manually.
I got the pipeline working by running "npm install" as a step in the pipeline. So add this to your Jenkinsfile before the 'Build' stage:
stage ('install app') {
steps {
sh "npm install"
}
}
I don't know why this happens but it might have something to do with how Jenkins sets the context for the Docker build. I hope someone else can elaborate on this.