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Jenkins agent

OpenShift Container Platform provides three images that are suitable for use as Jenkins agents: the Base, Maven, and Node.js images.

The first is a base image for Jenkins agents:

  • It pulls in both the required tools, headless Java, the Jenkins JNLP client, and the useful ones including git, tar, zip, and nss among others.

  • It establishes the JNLP agent as the entrypoint.

  • It includes the oc client tooling for invoking command line operations from within Jenkins jobs.

  • It provides Dockerfiles for both Red Hat Enterprise Linux (RHEL) and localdev images.

Two more images that extend the base image are also provided:

  • Maven v3.5 image

  • Node.js v10 image and Node.js v12 image

The Maven and Node.js Jenkins agent images provide Dockerfiles for the Universal Base Image (UBI) that you can reference when building new agent images. Also note the contrib and contrib/bin subdirectories. They allow for the insertion of configuration files and executable scripts for your image.

Use and extend an appropriate agent image version for the your of OpenShift Container Platform. If the oc client version that is embedded in the agent image is not compatible with the OpenShift Container Platform version, unexpected behavior can result.

Jenkins agent images

The OpenShift Container Platform Jenkins agent images are available on quay.io or registry.redhat.io.

Jenkins images are available through the Red Hat Registry:

$ docker pull registry.redhat.io/openshift4/ose-jenkins:<v4.4.0>
$ docker pull registry.redhat.io/openshift4/jenkins-agent-nodejs-10-rhel7:<v4.4.0>
$ docker pull registry.redhat.io/openshift4/jenkins-agent-nodejs-12-rhel7:<v4.4.0>
$ docker pull registry.redhat.io/openshift4/ose-jenkins-agent-maven:<v4.4.0>
$ docker pull registry.redhat.io/openshift4/ose-jenkins-agent-base:<v4.4.0>

To use these images, you can either access them directly from quay.io or registry.redhat.io or push them into your OpenShift Container Platform container image registry.

Jenkins agent environment variables

Each Jenkins agent container can be configured with the following environment variables.

Variable Definition Example values and settings

JAVA_MAX_HEAP_PARAM, CONTAINER_HEAP_PERCENT, JENKINS_MAX_HEAP_UPPER_BOUND_MB

These values control the maximum heap size of the Jenkins JVM. If JAVA_MAX_HEAP_PARAM is set, its value takes precedence. Otherwise, the maximum heap size is dynamically calculated as CONTAINER_HEAP_PERCENT of the container memory limit, optionally capped at JENKINS_MAX_HEAP_UPPER_BOUND_MB MiB.

By default, the maximum heap size of the Jenkins JVM is set to 50% of the container memory limit with no cap.

JAVA_MAX_HEAP_PARAM example setting: -Xmx512m

CONTAINER_HEAP_PERCENT default: 0.5, or 50%

JENKINS_MAX_HEAP_UPPER_BOUND_MB example setting: 512 MiB

JAVA_INITIAL_HEAP_PARAM, CONTAINER_INITIAL_PERCENT

These values control the initial heap size of the Jenkins JVM. If JAVA_INITIAL_HEAP_PARAM is set, its value takes precedence. Otherwise, the initial heap size is dynamically calculated as CONTAINER_INITIAL_PERCENT of the dynamically calculated maximum heap size.

By default, the JVM sets the initial heap size.

JAVA_INITIAL_HEAP_PARAM example setting: -Xms32m

CONTAINER_INITIAL_PERCENT example setting: 0.1, or 10%

CONTAINER_CORE_LIMIT

If set, specifies an integer number of cores used for sizing numbers of internal JVM threads.

Example setting: 2

JAVA_TOOL_OPTIONS

Specifies options to apply to all JVMs running in this container. It is not recommended to override this value.

Default: -XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap -Dsun.zip.disableMemoryMapping=true

JAVA_GC_OPTS

Specifies Jenkins JVM garbage collection parameters. It is not recommended to override this value.

Default: -XX:+UseParallelGC -XX:MinHeapFreeRatio=5 -XX:MaxHeapFreeRatio=10 -XX:GCTimeRatio=4 -XX:AdaptiveSizePolicyWeight=90

JENKINS_JAVA_OVERRIDES

Specifies additional options for the Jenkins JVM. These options are appended to all other options, including the Java options above, and can be used to override any of them, if necessary. Separate each additional option with a space; if any option contains space characters, escape them with a backslash.

Example settings: -Dfoo -Dbar; -Dfoo=first\ value -Dbar=second\ value

Jenkins agent memory requirements

A JVM is used in all Jenkins agents to host the Jenkins JNLP agent as well as to run any Java applications such as javac, Maven, or Gradle.

By default, the Jenkins JNLP agent JVM uses 50% of the container memory limit for its heap. This value can be modified by the CONTAINER_HEAP_PERCENT environment variable. It can also be capped at an upper limit or overridden entirely.

By default, any other processes run in the Jenkins agent container, such as shell scripts or oc commands run from pipelines, cannot use more than the remaining 50% memory limit without provoking an OOM kill.

By default, each further JVM process that runs in a Jenkins agent container uses up to 25% of the container memory limit for it’s heap. It might be necessary to tune this limit for many build workloads.

Jenkins agent Gradle builds

Hosting Gradle builds in the Jenkins agent on OpenShift Container Platform presents additional complications because in addition to the Jenkins JNLP agent and Gradle JVMs, Gradle spawns a third JVM to run tests if they are specified.

The following settings are suggested as a starting point for running Gradle builds in a memory constrained Jenkins agent on OpenShift Container Platform. You can modify these settings as required.

  • Ensure the long-lived Gradle daemon is disabled by adding org.gradle.daemon=false to the gradle.properties file.

  • Disable parallel build execution by ensuring org.gradle.parallel=true is not set in the gradle.properties file and that --parallel is not set as a command line argument.

  • To prevent Java compilations running out-of-process, set java { options.fork = false } in the build.gradle file .

  • Disable multiple additional test processes by ensuring test { maxParallelForks = 1 } is set in the build.gradle file.

  • Override the Gradle JVM memory parameters by the GRADLE_OPTS, JAVA_OPTS or JAVA_TOOL_OPTIONS environment. variables.

  • Set the maximum heap size and JVM arguments for any Gradle test JVM by defining the maxHeapSize and jvmArgs settings in build.gradle, or though the -Dorg.gradle.jvmargs command line argument.

Jenkins agent pod retention

Jenkins agent pods, also known as slave pods, are deleted by default after the build completes or is stopped. This behavior can be changed by the Kubernetes plug-in Pod Retention setting. Pod retention can be set for all Jenkins builds, with overrides for each pod template. The following behaviors are supported:

  • Always keeps the build pod regardless of build result.

  • Default uses the plug-in value (pod template only).

  • Never always deletes the pod.

  • On Failure keeps the pod if it fails during the build.

You can override pod retention in the pipeline Jenkinsfile:

podTemplate(label: "mypod",
  cloud: "openshift",
  inheritFrom: "maven",
  podRetention: onFailure(), (1)
  containers: [
    ...
  ]) {
  node("mypod") {
    ...
  }
}
1 Allowed values for podRetention are never(), onFailure(), always(), and default().

Pods that are kept might continue to run and count against resource quotas.