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CJE: Jenkins Installation, Configuration, and Administration

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Jenkins Installation, Configuration, and Administration

What this domain covers

This domain tests whether you can stand up a Jenkins controller from scratch, choose the right distribution, wire it to a persistent home directory, and administer it day to day without corrupting state. Expect questions on the WAR file versus native packages, JENKINS_HOME layout, JVM and system properties, the setup wizard, and Configuration as Code.

Core rules

  • Two release lines. Weekly releases ship every week with new features; LTS releases are cut roughly every 12 weeks from a weekly baseline and receive backported fixes. Controlled production controllers should run LTS.
  • JENKINS_HOME holds everything mutable: config.xml, jobs/, users/, plugins/, secrets/, workspace/, logs/. Backing up Jenkins means backing up this directory with the controller quiesced.
  • Startup. java -jar jenkins.war --httpPort=8080 runs on the embedded Winstone container. Useful flags: --prefix=/jenkins for a reverse-proxy sub-path, --httpListenAddress=127.0.0.1 to bind loopback, --argumentsRealm.passwd.admin=... for scripted bootstrap. Container images read JAVA_OPTS and JENKINS_OPTS.
  • JVM sizing. Set heap with -Xmx (e.g. -Xmx4g). Controller heap is dominated by in-memory job, build, and agent metadata, not build output, so give it its own dedicated disk rather than relying on memory.
  • Unlock. The first start writes a one-time password to $JENKINS_HOME/secrets/initialAdminPassword; the wizard then offers suggested plugins and the first admin account.
  • Configuration as Code. The configuration-as-code plugin loads jenkins.yaml from CASC_JENKINS_CONFIG (path, directory, or URL) and exports the live config via /configuration-as-code/export. Secrets can be sourced from environment variables so the YAML stays free of cleartext.
  • CLI. java -jar jenkins-cli.jar -s https://ci.example/ -auth user:token exposes install-plugin, safe-restart, build, list-plugins.

Worked example

You must move a controller from http://host:8080/ to https://ci.example.com/jenkins/ behind nginx. Start Jenkins with --prefix=/jenkins bound to 127.0.0.1, terminate TLS at nginx, and proxy with proxy_pass http://127.0.0.1:8080/jenkins/;. Reasoning: Jenkins generates absolute URLs from the prefix, so the proxy location and --prefix must agree exactly; changing the prefix later leaves stale URLs in job configs and webhook payloads.

Traps

Editing config.xml while Jenkins is running - the in-memory model overwrites it on save. Confusing plugins you uninstalled with plugins that are merely disabled. Assuming JENKINS_HOME is only jobs/ and missing secrets/ in a backup. Running weekly releases on a controlled production controller.