Rhcos Build Pipeline

RHCOS Build Pipeline

Knowledge about the RHEL CoreOS build pipeline, Jenkins jobs, and multi-architecture builds.

Related: rhcos-repositories, rhcos-artifacts, rhcos-versions

Build Process Overview

RHCOS is built in two stages:

Stage 1: Base Image (build + build-arch jobs)

• Input: rhel-coreos-config repository (contains fedora-coreos-config as submodule)
• The build job runs for x86_64 and triggers build-arch for other architectures
• build-arch runs in parallel for aarch64, ppc64le, s390x
• All build-arch jobs must succeed for the pipeline to continue
• Output: Bootable container with RHEL/CentOS Stream content only (no OpenShift components)

Stage 2: Node Image (build-node-image job)

• Input: Base image from Stage 1 + openshift/os Containerfile
• Adds OpenShift packages: kubelet, cri-o, oc, etc.
• Output: rhel-coreos or stream-coreos image in OCP release payload

Jenkins Jobs

Build and Build-Arch Relationship

The build job orchestrates multi-architecture builds:

1. build job starts for x86_64
2. build triggers build-arch jobs for aarch64, ppc64le, s390x in parallel
3. build waits for all build-arch jobs to complete
4. If any build-arch job fails, the parent build job fails
5. Only when all architectures succeed does build-node-image proceed

When investigating a build failure, check if the root cause is in build-arch:

# Check if build-arch jobs failed
coreos-tools jenkins builds list build-arch --status FAILURE -n 5

# Get the triggering build job number from build-arch parameters
coreos-tools jenkins builds info build-arch <build-number>

Architectures

Build Scheduling

build-mechanical Job

The build-mechanical job is the main scheduler for RHCOS base image builds:

• Schedule: Daily at 10:00 UTC (cron: 0 10 * * *)
• Source: jobs/build-mechanical.Jenkinsfile in fedora-coreos-pipeline
• Behavior: Triggers build jobs sequentially for all mechanical streams

Execution Order:

c10s → c9s → rhel-10.2 → rhel-9.8 → rhel-9.6

Due to sequential execution (each build takes 2-3 hours), later streams start much later:

• c10s: ~10:00 UTC
• rhel-9.6: ~17:00-18:00 UTC (last in queue)

Checking Schedule

# View recent build-mechanical runs
coreos-tools jenkins builds list build-mechanical -n 10

# Check what streams were triggered in a specific run
coreos-tools jenkins builds log build-mechanical <build-number> | grep "Triggering build"

FORCE Parameter

The FORCE parameter controls whether to rebuild even if no changes are detected.

When FORCE is needed:

• Forcing an immediate rebuild to pick up new packages from repos (before next scheduled run)
• Recovering from a failed build that left stale state

When FORCE is NOT needed:

• Normal scheduled builds (they run daily and usually produce new builds)
• The build-mechanical job does NOT use FORCE; it relies on cosa detecting changes

How cosa detects changes:

• Checks if source config (rhel-coreos-config) commit changed
• Checks package manifest/lockfile changes
• Does NOT automatically detect RHEL repo package updates (mechanical streams don't use strict lockfiles)

Versionlock Mechanism

During build-node-image, packages from the base image are versionlocked to prevent unexpected upgrades. This is done dynamically at build time, not via static config files.

How It Works

1. build job creates base image with packages at specific versions (e.g., NetworkManager-1.52.0-9)
2. build-node-image runs rpm-ostree experimental compose treefile-apply
3. This creates versionlocks for ALL packages in the base image
4. New packages can be installed, but locked packages cannot be upgraded

You can see this in the build logs:

Adding versionlock on: NetworkManager-1:1.52.0-9.el9_6.*
Adding versionlock on: NetworkManager-tui-1:1.52.0-9.el9_6.*
...

Version Skew Problem

If a new package in the repos requires a newer version of a locked package, DNF fails:

Error: package NetworkManager-ovs-1:1.52.0-10 requires NetworkManager = 1:1.52.0-10,
       but package NetworkManager-1:1.52.0-9 is filtered out by exclude filtering

Typical scenario:

1. Base image built with package version X
2. RHEL repos updated with package version X+1
3. A new dependency package requires version X+1
4. build-node-image fails because version X is locked and X+1 is excluded

Fix: Rebuild the base image (build job) to pick up the newer package version:

coreos-tools jenkins jobs build build --param STREAM=rhel-9.6

Job Commands

# List all jobs
coreos-tools jenkins jobs list

# Get job info (health, last builds)
coreos-tools jenkins jobs info <job-name>

# Trigger a build
coreos-tools jenkins jobs build <job-name> --param STREAM=<stream>

# Trigger a forced build (bypass "no changes" detection)
coreos-tools jenkins jobs build <job-name> --param STREAM=<stream> --param FORCE=true

# View build queue
coreos-tools jenkins queue list

# List nodes
coreos-tools jenkins nodes list