OCP

Lessons learned from using Jenkins on containers a.k.a CloudBees CI

Adrian Citu

Recently, I encountered some issues with a (Jenkins) declarative pipeline running on CloudBees CI, specifically for a Python project. The CloudBees CI instance was operating within an OpenShift Platform (OCP) cluster, and I was employing the Kubernetes plugin for managing agents/slaves.

Here are the lessons learned, some of them linked to OCP/K8S, some linked to CloudBees CI, some linked to Python and some other linked to all this technologies put together:

  1. Make sure that the application packaged as image is running properly when executed from a plain Docker/Podman system.
  2. The container/s will be run into a pod so the (Dockerfile) WORKDIR instruction (if defined) in the container/s will be ignored. If you need to define a working directory then you should specify this into the pod definition via pod.spec.template.spec.containers.workingDir.
  3. The default working directory for the running container/s will be (Jenkins) ${env.WORKSPACE}.
  4. If the pipeline code is fetched from a Git repository then the repository will be automatically mapped as volume inside the container/s under the folder ${env.WORKSPACE}
  5. For container/s running Python the sys.path variable will be: ‘ ‘, ${env.WORKSPACE}, container.PYTHONPATH  in this specific order, where ‘ ‘ is the current directory which by default will be ${env.WORKSPACE} (see point number 3). So the default sys.path will be: ${env.WORKSPACE}, ${env.WORKSPACE}, container.PYTHONPATH 
  6. The (nasty) side effect of the previous point is that if there are Python modules in Git repository (which is mounted in the container, see point number 4) and in the container/s, having the same name, then the module/s from the Git repository will be used for execution and not the one from container/s.
  7. If you want to revert the situation from previous point the only way is to play on the first element of the sys.path variable which will always be the current directory (‘ ‘). If the first element of the sys.path is / then the container/s modules will be used for execution instead of the Git repository modules.
  8. The sys.path variable is computed at runtime by the Python interpreter so it cannot be modified in advance (like the PYTHONPATH environment variable) prior to the execution of a program.