Jenkins Pipeline Image.inside runs shells command in workspace, not inside container

Question

im having troubles contructiong my Jenkins Pipeline for what should be an easy scenario.

Im using DockerDesktop running a Jenkins image (https://hub.docker.com/r/jenkinsci/blueocean/). I have a standard react-app that i want to build and run tests after my commits.

The Webhooks configurations already works, but the commands i run inside my Jenkinsfile doesn't seem to work as i expected:

This is my current Jenkinsfile:

node {
def app

stage('Clone repository') {
    checkout scm
}

stage('Build image') {
    app = docker.build("getintodevops/hellonode", "-f Dockerfile.dev ./")
}

stage('Test image') {
    app.inside {
        sh 'pwd'
        sh 'npm run build'
    }
}

}

the Dockerfile-dev looks like this:

FROM node:alpine

COPY ./package.json ./
RUN ["npm", "install"]
COPY ./src/ ./src/
COPY ./public/ ./public/

what i expected was that the commands inside the stage(Test image) would run inside a container with the image i've just build, but the pwd command shows that the commands are exec'd inside the jenkins workspace,containging basically what i have committed on github (/src, /public, package.json ecc..), so when npm run build is launched i get an error for missing the node_modules.

Am I missing something? Shouldn't the commands run on the built image, which i verified has all the necessary folders?

Let me know if other files or configurations im using are necessary

P.S. I've also tried using this kind of Jenkinsfile, but i always have the same issue(even if the agent is defined outside the stage):

pipeline {
  agent none

  stages {
    stage('Build') {
      agent{
        dockerfile {
          filename 'Dockerfile.dev'
        }
      }

      steps {
        sh "npm run build"
      }
    }

Andy Shinn Andy Shinn · Accepted Answer · 2020-05-03T19:01:53

Am I missing something? Shouldn't the commands run on the built image, which i verified has all the necessary folders?

Yes. I'll try to explain a little bit about the part you are missing.

When a Jenkins pipeline runs a stage as a Docker container it does a couple things behind the scenes:

The workspace gets mounted to the container at runtime (as you have observed).
The working directory gets set to this workspace folder (which is why commands show your workspace files in the container).
The container is run with the user ID of the Jenkins user.
Various other options are passed to the container (such as environment variables).

Knowing this, there are two possible solutions you could do (and they each have pros and cons):

Option 1

You can ignore the node_modules and code in the container and essentially just use it as a NodeJS environment. Your Jenkins pipeline would then be responsible for doing npm install and other test commands. This would keep node_modules in your workspace. But you would also have a built container image that could potentially be deployed somewhere.

This also potentially works around issues where node_modules contain binaries that potentially differ between the Jenkins Docker image (which I believe is based on Debian, though, they do have a Alpine variant).

Option 2

If you don't want Jenkins workspace to be the source of truth then you would need to go into the location of the node_modules in the container. This appears to just be / according to your Dockerfile. You could potentially modify your steps to be inside a dir like:

pipeline {
  agent none

  stages {
    stage('Build') {
      agent {
        dockerfile {
          filename 'Dockerfile.dev'
        }
      }

      steps {
        dir("/") {
          sh "npm run build"
        }
      }
    }
  }
}

Option 2 has potential permissions issues since your Docker image builds and creates files as root but the Jenkins pipeline will run as the Jenkins user.

Jenkins Pipeline Image.inside runs shells command in workspace, not inside container

1 Answers

Option 1

Option 2