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Agent Guide for kURL

This guide is for AI agents working in the kURL repository. It explains how the project is organized, how changes are made (especially add-on updates), how to test, and how the repository relates to the kURL-testgrid testing platform.

1. Project overview

kURL is a Kubernetes installer for air-gapped and online clusters, maintained by Replicated. It automates the tasks a cluster administrator must perform before and after running kubeadm init to create a production-ready Kubernetes cluster.

A user posts a YAML Installer manifest to the kURL.sh API and receives a deterministic hash. That hash can be used to fetch an install script (https://kurl.sh/<hash>) or an air-gap bundle (https://kurl.sh/bundle/<hash>.tar.gz). The installer then downloads pre-built add-on tarballs and host packages from the kurl-sh S3 bucket and executes the install/upgrade on the target node.

The kURL project has two main repositories:

  • kURL (github.com/replicatedhq/kURL) — builds the installer scripts, add-on packages, host packages, Go utilities, and the public API registry.
  • kURL-testgrid (github.com/replicatedhq/kURL-testgrid) — the test automation platform that provisions real Linux VMs, runs kURL installers, executes Sonobuoy conformance tests, and publishes results at https://testgrid.kurl.sh.

2. Repository structure

Key directories in this repo:

Directory Purpose
addons/<name>/<version>/ Add-on definitions, one directory per version. Each version contains at minimum Manifest, install.sh, and usually host-preflight.yaml.
bin/ Build, packaging, and release helper scripts.
bundles/ Docker build contexts for host packages (Kubernetes RPM/DEB repos per OS).
cmd/ Go entrypoints; cmd/kurl is the main CLI binary.
hack/ Local development helpers, test data, and test Dockerfiles.
kurl_util/ Go utilities built into binaries and the replicated/kurl-util Docker image.
packages/ Host-package definitions (e.g., kubernetes, host/openssl, host/fio).
pkg/ Go library code for the kurl CLI.
scripts/ The bash installer source (install.sh, join.sh, upgrade.sh, tasks.sh, common/).
testgrid/specs/ Testgrid YAML specs for OS images and test scenarios.
tools/ Additional tooling.
web/src/installers/ Frontend version registry; versions.js lists available add-on versions.
.github/workflows/ CI/CD workflows.

Important documents:

  • README.md — project overview and community links.
  • ARCHITECTURE.md — manifest format, API services, object storage, add-on lifecycle, release workflows.
  • CONTRIBUTING.md — development workflow, remote testing, environment setup.
  • addons/README.md — add-on structure, Manifest directives, lifecycle hooks.
  • testgrid/specs/README.md — how Testgrid specs work.
  • docs/arch/adr-003-external-addons.md — external add-on model (kotsadm).
  • CODEOWNERS — global owner @replicatedhq/embedded-kubernetes.

3. How to approach changes

General workflow

  1. Identify the scope. Is this a core installer change, an add-on change, a Testgrid-only change, or a version bump? Core scripts live in scripts/. Add-ons live in addons/<name>/<version>/. Testgrid specs live in testgrid/specs/ and in add-on template/testgrid/ directories.
  2. Make the minimal change. Edit only the source files. Generated files (e.g., build/, dist/, addons-gen.json, supported-versions-gen.json) are produced by make targets and should not be hand-edited.
  3. Keep scripts/Manifest in sync with hack/testdata/manifest/clean. make test compares these two files and fails if they differ. If you modify scripts/Manifest, update the test data copy as well.
  4. Run local tests. See the Testing section below.
  5. Let CI run Testgrid for add-on changes. The test-addon-pr.yaml workflow detects modified add-ons and queues Testgrid runs automatically.

When working on a remote Linux VM

The install scripts are not macOS-compatible. For real-world testing, use make watchrsync after exporting:

export GOOS=linux
export GOARCH=amd64
export DOCKER_DEFAULT_PLATFORM=linux/amd64
export REMOTES="USER@TARGET_SERVER_IP"
make watchrsync

bin/watchrsync.js continuously syncs local builds to ~/kurl on the remote server.

macOS local-build prerequisites

Install gnu-sed and md5sha1sum (e.g., via Homebrew) to run local build scripts. Apple Silicon hosts should also set GOOS=linux, GOARCH=amd64, and DOCKER_DEFAULT_PLATFORM=linux/amd64 before building.

4. How to update add-ons

Add-ons are the primary extension point of kURL. Each add-on is a versioned directory with a declarative Manifest, an install.sh shell script, and optional templates.

Add-on structure

addons/<name>/<version>/
  Manifest                # assets, images, host packages to download
  install.sh              # defines a function named exactly like the add-on
  host-preflight.yaml     # optional Troubleshoot.sh preflight spec
  assets/                 # generated at build time
  images/                 # generated at build time
  ...

The install.sh must define a function with the exact add-on name (e.g., function containerd()). Lifecycle hooks are defined in addons/README.md:

  • addon_fetch
  • addon_load
  • addon_preflights
  • addon_pre_init
  • addon_install (required)
  • addon_already_applied
  • addon_join
  • addon_post_init
  • addon_outro

Manifest directives

Common directives (see addons/README.md for the full list):

image pause k8s.gcr.io/pause:3.6
yum libzstd
yum8 container-selinux
yumol <pkg>
apt containerd
apt24 containerd
yum2023 containerd
asset runc https://github.com/opencontainers/runc/releases/download/v1.3.5/runc.amd64
dockerout rhel-9 addons/containerd/template/Dockerfile.rhel9 1.7.29

Adding a new add-on version

  1. Create or generate the version directory under addons/<name>/<version>/.
  2. Ensure it contains Manifest, install.sh, and host-preflight.yaml.
  3. Add or update Testgrid specs under addons/<name>/template/testgrid/*.yaml if needed.
  4. Register the new version in web/src/installers/versions.js.
  5. Run make generate-addons to update addons-gen.json and supported-versions-gen.json.
  6. Build the package locally: make dist/<name>-<version>.tar.gz.
  7. Test with Testgrid or via make watchrsync on a remote Linux VM.

Templated add-ons

Some add-ons are auto-generated from a template/ directory:

  • addons/containerd/template/ — script.sh, Dockerfiles, and testgrid specs.
  • addons/flannel/template/ — generate.sh, base/, and testgrid specs.

For templated add-ons, changes should be made in the template, then the version is regenerated. Do not hand-edit generated version directories.

External add-ons

kotsadm is an external add-on (see docs/arch/adr-003-external-addons.md). It is built and released from replicatedhq/kots, publishes a versions.json, and the import-external-addons action copies packages into the kURL S3 bucket. The kURL API merges these with internal versions.

5. Testing

Local tests

# Lint, vet, Go tests, and manifest check
make test

# Go tests only
go test ./cmd/... ./pkg/...
make -C kurl_util test

# Shell tests in Docker
make docker-test-shell

# Containerd configure/upgrade regression tests
make docker-test-containerd

# Build a specific add-on package
make dist/containerd-1.7.29.tar.gz

# Build Kubernetes host packages for a specific OS
make build/packages/kubernetes/1.31.14/ubuntu-22.04
make build/packages/kubernetes/1.31.14/images

Testgrid integration

Testgrid is the primary end-to-end testing platform. It is a separate repository (kURL-testgrid), but the specs that drive it live in this repo:

  • testgrid/specs/os-*.yaml — OS image pools.
  • testgrid/specs/deploy.yaml, full.yaml, latest.yaml, storage-migration.yaml, customer-migration-specs.yaml, k8s-upgrade.yaml — test scenarios.

Active CI usage is documented in testgrid/specs/README.md. Workflows submit runs via the replicated/tgrun Docker image:

tgrun queue --spec <spec> --os-spec <os-spec> --ref <ref> --api-token <token>

Add-ons can define their own specs under addons/<name>/template/testgrid/*.yaml. During add-on tests, bin/test-addon.sh substitutes __testver__ and __testdist__ placeholders in the spec templates.

Testgrid credentials for local runs

A few local helpers (for example, bin/test-addon.sh and the testgrid-failure-analysis skill) read Testgrid secrets from environment variables. Put these values in a .env file at the repository root (not .envrc) and keep the file out of version control. .env is already listed in .gitignore.

If you use direnv, the .envrc in the repo root will automatically source .env when you enter the directory. Example variables to set in .env (replace ... with your own secrets):

export TESTGRID_API_TOKEN=...
export TESTGRID_AGE_PASSPHRASE=...

Never commit real values, .env files, or .envrc to the repository.

How Testgrid works (high-level)

  1. A user or CI invokes tgrun queue with a test spec and OS spec.
  2. tgrun submits each installer spec to the kURL API to get a runnable URL/hash.
  3. tgrun enqueues planned VM instances to the TGAPI (Testgrid API).
  4. tgrun run (the runner daemon) polls TGAPI, creates KubeVirt VMs on bare-metal hosts, and runs the test scripts.
  5. VMs report status, logs, Sonobuoy results, and support bundles back to TGAPI.
  6. The web UI reads TGAPI and displays results at https://testgrid.kurl.sh.

Key Testgrid API endpoints for public data:

  • POST /api/v1/run/{refId} — get a run with its instances.
  • GET /api/v1/instance/{instanceId}/logs — main instance logs.
  • GET /api/v1/instance/{nodeId}/node-logs — per-node logs.
  • GET /api/v1/instance/{instanceId}/sonobuoy — Sonobuoy results.

6. Build and release

Primary build targets

make build/install.sh      # single-file installer script
make build/join.sh         # single-file join script
make build/upgrade.sh      # single-file upgrade script
make build/tasks.sh        # single-file tasks script
make dist/<addon>-<version>.tar.gz
make dist/common.tar.gz
make dist/kurl-bin-utils-<version>.tar.gz
make build/bin/kurl        # kurl CLI
make kurl-util-image       # replicated/kurl-util:alpha

Script assembly

build/install.sh is assembled from scripts/install.sh by inlining every file referenced by . $DIR/scripts/... between the # Magic begin and # Magic end markers. The same pattern applies to join.sh, upgrade.sh, and tasks.sh.

CI/CD workflows

  • .github/workflows/build-test.yaml — runs on every PR (Go mod tidy, kurl_util tests, kurl build, shell tests, containerd tests).
  • .github/workflows/deploy-staging.yaml — runs on every merge to main. Builds packages, uploads to s3://kurl-sh/staging/<version>-<sha>/, generates addons-gen.json/supported-versions-gen.json, and queues Testgrid.
  • .github/workflows/deploy-prod.yaml — triggered by tags v*.*.*. Copies staging packages to s3://kurl-sh/dist/<version>/, creates a GitHub release, generates SBOMs, and queues Testgrid.
  • .github/workflows/test-addon-pr.yaml — detects modified add-ons in PRs and invokes test-addon.yaml for each.
  • .github/workflows/test-addon.yaml — builds a single add-on package, uploads to S3, and queues Testgrid using the add-on's template specs.
  • .github/workflows/update-<addon>.yaml — scheduled workflows that generate PRs for new upstream add-on versions (e.g., update-containerd.yaml, update-flannel.yaml).

Release versioning

  • Production tags: vYYYY.MM.DD-# (e.g., v2024.07.02-0).
  • Staging versions: <latest-tag>-<short-sha> (e.g., v2024.07.02-0-5af497c).
  • make tag-and-release creates a production tag and triggers the release workflow.
  • The current release is advertised by s3://kurl-sh/dist/VERSION and s3://kurl-sh/staging/VERSION.

7. Conventions and gotchas

  • Add-on directory names are lowercase (containerd, flannel, rook).
  • Version directories use the upstream version string (1.7.29, 2.8.1).
  • All shell functions in an add-on should be prefixed with the add-on name to avoid collisions (e.g., containerd_configure).
  • versions.js is the source of truth for selectable add-on versions. The generated addons-gen.json and supported-versions-gen.json are produced by make generate-addons.
  • scripts/Manifest must stay in sync with hack/testdata/manifest/clean; make test enforces this.
  • Generated version directories should not be hand-edited for templated add-ons; edit the template and regenerate.
  • Testgrid OS filtering is opt-out via unsupportedOSIDs; there is no supportedOSIDs.
  • Linux/amd64 required for runtime testing. The scripts are not macOS-compatible; use a remote Linux VM or Docker.
  • On Apple Silicon, set GOOS=linux, GOARCH=amd64, and DOCKER_DEFAULT_PLATFORM=linux/amd64 before building.
  • Keep secrets in .env. .env and .envrc are gitignored. If you use direnv, .envrc will automatically load .env; otherwise, source it manually. Never commit secrets, .env, or .envrc.

8. Useful commands

# Full local test suite
make test

# Build the installer script
make build/install.sh

# Build an add-on package
make dist/<addon>-<version>.tar.gz

# Generate add-on metadata
make generate-addons

# Watch and sync builds to a remote Linux test VM
export GOOS=linux GOARCH=amd64 DOCKER_DEFAULT_PLATFORM=linux/amd64 REMOTES="USER@IP"
make watchrsync

# Run shell tests in Docker
make docker-test-shell

9. Key files for agents to know

  • Makefile — primary build orchestration.
  • scripts/install.sh — entrypoint source with Magic begin/end markers.
  • scripts/Manifest and hack/testdata/manifest/clean — must stay in sync.
  • scripts/common/addon.sh — add-on runtime orchestration.
  • bin/save-manifest-assets.sh — downloads/builds all assets described by a Manifest.
  • web/src/installers/versions.js — human-edited version registry.
  • addons-gen.json and supported-versions-gen.json — generated API metadata.
  • .github/workflows/deploy-staging.yaml and .github/workflows/deploy-prod.yaml — release pipelines.
  • .github/workflows/test-addon-pr.yaml — PR add-on testing.
  • bin/test-addon.sh — submits add-on Testgrid runs.
  • pkg/cli/commands.go — kurl CLI command tree.