How to define multiple containers in declarative pipeline?

This isnt a solution to your problem, but is some information I found after looking.

The KubernetesDeclarativeAgent only has a single containerTemplate. Whichever containerTemplate is at the bottom of your collection of containers will be the one that is used.

In your example it will be containtertwo.

You cant have multiple top level agents, and you cant have multiple kubernetes within an agent. And now you cant have multiple containers. I would prefer if an error or warning of some kind was thrown for this.

There are 2 work arounds I can think of. If you must use declarative, then you can add an agent to your stage, but this can lead to its own issues. The other is the scripted pipeline, which is what I am going to do.

The documentation on this leaves much to be desired.

You can achive that with the help of a pod template file. I use the following one to deploy my app on kubernetes:

apiVersion: v1kind: Podmetadata:  labels:    label: dockerspec:  containers:  - name: docker    image: jenkins/jnlp-agent-docker    command:    - cat    tty: true    volumeMounts:    - mountPath: '/var/run/docker.sock'      name: docker-socket  - name: kubectl    image: bitnami/kubectl    command:    - cat    tty: true  volumes:  - name: docker-socket    hostPath:      path: '/var/run/docker.sock'  securityContext:    runAsUser: 0

Then use this in a declarative pipeline:

stage('Deploy') {  when {    anyOf { branch 'master'; tag '' }  }  agent {    kubernetes {      defaultContainer 'kubectl' // All `steps` instructions will be executed by this container      yamlFile 'path/to/pod/template.yaml'    }  }  steps {    container('docker') {      sh 'echo This is executed in the docker container'    }  }}

You can also specify the template in the Jenkinsfile with the help of yaml option instead of yamlFile, you just need to use a multiline string there.