How do I specify a node type that has docker installed in Jenkinsfile? - docker

Question

I want to use docker to build my code. Not all jenkin slaves have docker installed, so if I just specify:
agent {
dockerfile true
}
It fails withe message "docker not found". This I believe because the docker is not installed in that corresponding jenkins slave/master that picked up the job. So my question is: How can I ensure that this jenkins job gets picked by a node that has docker installed?
If I use:
agent {
node {
label 'has-docker'
dockerfile true
}
}
I get the following error:
org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
WorkflowScript: 2: Only one agent type is allowed per agent section # line 2, column 5.
agent {
^
WorkflowScript: 2: No agent type specified. Must be one of [docker, dockerfile, label, any, none] # line 2, column 5.
agent {

Answer 1

Using two agent directives would resolve the issue:
agent none for the entire pipeline and a docker agent for the specific stage.
Your jenkinsfile should look like this:
pipeline{
agent none
stages{
stage('stage_name'){
agent {
dockerfile{
label 'slave-label'
dir 'relative/location/of/Dockerfile'
}
}
...
}
}
}

Answer 2

You can provide an extra argument label inside the docker block as documented here.
docker
Execute the Pipeline, or stage, with the given container which will be dynamically provisioned on a node pre-configured to accept Docker-based Pipelines, or on a node matching the optionally defined label parameter.
pipeline {
agent {
docker {
image 'node:14-alpine'
label 'docker-node'
}
}
stages {
...
}
}
Its similar if you're using dockerfile instead of docker.
pipeline {
agent {
dockerfile {
filename 'Dockerfile'
dir 'build'
label 'docker-node'
}
}
stages {
...
}
}

Answer 3

You can use below one as example. (modify as per your need)
agent {
// Equivalent to "docker build -f Dockerfile.build --build-arg version=1.0.2 ./build/
dockerfile {
filename 'Dockerfile.build'
dir 'build'
label 'my-defined-label'
additionalBuildArgs '--build-arg version=1.0.2'
args '-v /tmp:/tmp'
}
}

Answer 4

You need to give the agents that have docker installed a common label and use that label inside the agent section for the pipeline. The jenkins documentation state the following for the label tag when defining a node.
Labels (or tags) are used to group multiple agents into one logical
group. For example, if you have multiple Windows agents and you have a
job that must run on Windows, then you could configure all your
Windows agents to have the label windows, and then tie that job to
this label. This would ensure that your job runs on one of your
Windows agents, but not on any agents without this label.
Labels do not necessarily have to represent the operating system on
the agent; you can also use labels to note the CPU architecture, or
that a certain tool is installed on the agent.
Multiple labels must be separated by a space. For example, windows
docker would assign two labels to the agent: windows and docker.
Labels may contain any non-space characters, but you should avoid
special characters such as any of these: !&|<>(), as other Jenkins
features allow for defining label expressions, where these characters
may be used.
In your case, do the same by labeling nodes that have docker installed with a common label such as `docker
As for the error you are encountering, the fix is mentioned here
agent {
docker {
dockerfile true
label 'docker'
}
}