Docker agent volume mount in Jenkins pipeline not working as expected - docker

Question

Following snippet with volume mount creates the maven dependencies under $JENKINS_HOME/workspace/<project-name>/? (Question Mark) instead of under $HOME/.m2/
Note that settings.xml mirror to our internal repository. And the instructions on how to mount has been directly taken from jenkins.io
Anyone has any clue why is this happening?
pipeline {
agent {
docker {
image 'maven:3-alpine'
args '-v /tmp/jenkins/.m2:/root/.m2:rw,z'
}
}
stages {
stage('Build') {
steps {
sh 'mvn clean install -s settings.xml'
}
}
}
}
This is not as simple as using Docker in standalone. I have created /var/jenkins/.m2 directory on Jenkins slave where the build would be running. Ensured the new directory has 775 permission (although that may not be required) and also changed the owner to be the same as what is for "/var/opt/slave/workspace/pipeline_test" (got this path based on logs below)
$ docker login -u dcr-login -p ******** https:// nexus.corp.zenmonics.com:8449
Login Succeeded
[Pipeline] {
[Pipeline] sh
+ docker inspect -f . nexus.corp.zenmonics.com:8449/maven:3-alpine
.
[Pipeline] withDockerContainer
cucj1sb3 does not seem to be running inside a container
$ docker run -t -d -u 1002:1002 -v /tmp/jenkins/.m2:/root/.m2:rw,z -w
/var/opt/slave/workspace/pipeline_test -v /var/opt/slave/workspace/pipeline_test:/var/opt/slave/workspace/pipeline_test:rw,z -v /var/opt/slave/workspace/pipeline_test#tmp:/var/opt/slave/workspace/pipeline_test#tmp:rw,z -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** -e ******** nexus.corp.zenmonics.com:8449/maven:3-alpine cat
$ docker top c7282468dbb6952aadbe4bb495757e7047122b179c81516645ba23759b78c366 -eo pid,comm
This statement on official maven image at Docker Hub (https://hub.docker.com/_/maven) makes me feel the volume mount is updated
To create a pre-packaged repository, create a pom.xml with the
dependencies you need and use this in your Dockerfile.
/usr/share/maven/ref/settings-docker.xml is a settings file that
changes the local repository to /usr/share/maven/ref/repository, but
you can use your own settings file as long as it uses
/usr/share/maven/ref/repository as local repo.

Answer 1

The documentation at : https://jenkins.io/doc/book/pipeline/docker/ is misleading and waste of time when it comes to volume mounting.
When Docker container is created its created with user 1002 and group 1002. The user 1002 doesn't have access to /root/.m2 and only has access to the working directory injected into the container.
Dockerfile
FROM maven:3-alpine
COPY --chown=1002:1002 repository/ /usr/share/maven/ref/repository/
RUN chmod -R 775 /usr/share/maven/ref/repository
COPY settings.xml /usr/share/maven/ref/
Settings.xml
<localRepository>/usr/share/maven/ref/repository</localRepository>
Docker command
docker build -t <server>:<port>/<image-name>:<image-tag> .
docker push <server>:<port>/<image-name>:<image-tag>
docker volume create maven-repo
Jenkinsfile
pipeline {
agent('linux2') {
docker {
label '<slave-label-here>'
image '<image-name>:<image-tag>'
registryUrl 'https://<server>:<port>'
registryCredentialsId '<jenkins-credentials-for-docker-login>'
args '-v maven-repo:/usr/share/maven/ref/repository/'
}
}
parameters {
booleanParam(name: 'SONAR', defaultValue: false, description: 'Select this option to run SONAR Analysis')
}
stages {
stage('Build') {
steps {
sh 'mvn clean install -s /usr/share/maven/ref/settings.xml -f pom.xml'
}
}
}
}

Answer 2

As #masseyb mentions in the comments, Jenkins treat $HOME as current building context.
And there are two workarounds:
a) use Jenkins plugin to set Env variable
You can use Envinject Plugin to set environment variables in Jenkins.
b) specify absolute path instead of $HOME/.m2
You can specify absolute path for .m2, e.g.:
pipeline {
agent {
docker {
image 'maven:3-alpine'
args '-v /home/samir-shail/.m2:/root/.m2'
}
}
stages {
stage('Build') {
steps {
sh 'mvn -B'
}
}
}
}
Note: please check that Jenkins has access to yours $HOME/.m2/ directory.