This document describes a high level overview how Jenkins Operator works.
The Jenkins Operator design incorporates the following concepts:
- watches any changes of manifests and maintain the desired state according to deployed custom resource manifest
- implements the main reconciliation loop which consists of two smaller reconciliation loops - base and user
Base reconciliation loop takes care of reconciling base Jenkins configuration, which consists of:
- Ensure Manifests - monitors any changes in manifests
- Ensure Jenkins Pod - creates and verifies status of Jenkins master Pod
- Ensure Jenkins Configuration - configures Jenkins instance including hardening, initial configuration for plugins, etc.
- Ensure Jenkins API token - generates Jenkins API token and initialized Jenkins client
User reconciliation loop takes care of reconciling user provided configuration, which consists of:
- Ensure Restore Job - creates Restore job and ensures that restore has been successfully performed
- Ensure Seed Jobs - creates Seed Jobs and ensures that all of them have been successfully executed
- Ensure User Configuration - executed user provided configuration, like groovy scripts, configuration as code or plugins
- Ensure Backup Job - creates Backup job and ensures that backup has been successfully performed
Operator state is kept in custom resource status section, which is used for storing any configuration events or job statuses managed by the operator. It helps to maintain or recover desired state even after operator or Jenkins restarts.
The operator or Jenkins instance can be restarted at any time and any operation should not block the reconciliation loop. Taking this into account we implemented custom jobs API for executing system jobs (seed jobs, groovy scripts, etc.) according to the operator lifecycle.
Main assumptions are:
- do not block reconciliation loop
- fire job, requeue reconciliation loop and verify job status next time
- handle retries if case of failure
- handle build expiration (deadline)
- keep state in the custom resource status section
Jenkins Operator is fully compatible with jenkins:lts docker image and does not introduce any hidden changes there. If needed, the docker image can easily be changed in custom resource manifest as long as it supports standard Jenkins file system structure.