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Watching for source changes
In this guide you’ll be developing a Kubernetes controller with Kubebuilder that subscribes to GitRepository events and reacts to revision changes by downloading the artifact produced by source-controller.
Prerequisites
On your dev machine install the following tools:
- go >= 1.20
- kubebuilder >= 3.0
- kind >= 0.17
- kubectl >= 1.25
Install Flux
Install the Flux CLI with Homebrew on macOS or Linux:
brew install fluxcd/tap/flux
Create a cluster for testing:
kind create cluster --name dev
Verify that your dev machine satisfies the prerequisites with:
flux check --pre
Install source-controller on the dev cluster:
flux install \
--namespace=flux-system \
--network-policy=false \
--components=source-controller
Clone the sample controller
You’ll be using
fluxcd/source-watcher as
a template for developing your own controller. The source-watcher was scaffolded with kubebuilder init.
Clone the source-watcher repository:
git clone https://github.com/fluxcd/source-watcher
cd source-watcher
Build the controller:
make
Run the controller
Port forward to source-controller artifacts server:
kubectl -n flux-system port-forward svc/source-controller 8181:80
Export the local address as SOURCE_CONTROLLER_LOCALHOST:
export SOURCE_CONTROLLER_LOCALHOST=localhost:8181
Run source-watcher locally:
make run
Create a Git source:
flux create source git test \
--url=https://github.com/fluxcd/flux2 \
--ignore-paths='/*,!/manifests' \
--tag=v0.41.2
The source-watcher will log the revision:
{"level":"info","ts":"2023-03-31T16:43:42.703+0200","msg":"New revision detected","controller":"gitrepository","controllerGroup":"source.toolkit.fluxcd.io","controllerKind":"GitRepository","GitRepository":{"name":"test","namespace":"flux-system"},"namespace":"flux-system","name":"test","reconcileID":"ef0fe80e-3952-4835-ae9d-01760c4eadde","revision":"v0.41.2@sha1:81606709114f6d16a432f9f4bfc774942f054327"}
Change the Git tag:
flux create source git test \
--url=https://github.com/fluxcd/flux2 \
--ignore-paths='/*,!/manifests' \
--tag=v2.0.0-rc.1
And source-watcher will log the new revision:
{"level":"info","ts":"2023-03-31T16:51:33.499+0200","msg":"New revision detected","controller":"gitrepository","controllerGroup":"source.toolkit.fluxcd.io","controllerKind":"GitRepository","GitRepository":{"name":"test","namespace":"flux-system"},"namespace":"flux-system","name":"test","reconcileID":"cc0f83bb-b7a0-4c19-a254-af9962ae39cd","revision":"v2.0.0-rc.1@sha1:658925c2c0e6c408597d907a8ebee06a9a6d7f30"}
The source-controller reports the revision under GitRepository.Status.Artifact.Revision in the format: <branch|tag>@sha1:<commit>.
How it works
The GitRepositoryWatcher controller does the following:
- subscribes to
GitRepositoryevents - detects when the Git revision changes
- downloads and extracts the source artifact
- writes the extracted dir names to stdout
type GitRepositoryWatcher struct {
client.Client
HttpRetry int
artifactFetcher *fetch.ArchiveFetcher
}
func (r *GitRepositoryWatcher) SetupWithManager(mgr ctrl.Manager) error {
r.artifactFetcher = fetch.NewArchiveFetcher(
r.HttpRetry,
tar.UnlimitedUntarSize,
os.Getenv("SOURCE_CONTROLLER_LOCALHOST"),
)
return ctrl.NewControllerManagedBy(mgr).
For(&sourcev1.GitRepository{}, builder.WithPredicates(GitRepositoryRevisionChangePredicate{})).
Complete(r)
}
// +kubebuilder:rbac:groups=source.toolkit.fluxcd.io,resources=gitrepositories,verbs=get;list;watch
// +kubebuilder:rbac:groups=source.toolkit.fluxcd.io,resources=gitrepositories/status,verbs=get
func (r *GitRepositoryWatcher) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
log := ctrl.LoggerFrom(ctx)
// get source object
var repository sourcev1.GitRepository
if err := r.Get(ctx, req.NamespacedName, &repository); err != nil {
return ctrl.Result{}, client.IgnoreNotFound(err)
}
artifact := repository.Status.Artifact
log.Info("New revision detected", "revision", artifact.Revision)
// create tmp dir
tmpDir, err := os.MkdirTemp("", repository.Name)
if err != nil {
return ctrl.Result{}, fmt.Errorf("failed to create temp dir, error: %w", err)
}
defer os.RemoveAll(tmpDir)
// download and extract artifact
if err := r.artifactFetcher.Fetch(artifact.URL, artifact.Digest, tmpDir); err != nil {
log.Error(err, "unable to fetch artifact")
return ctrl.Result{}, err
}
// list artifact content
files, err := os.ReadDir(tmpDir)
if err != nil {
return ctrl.Result{}, fmt.Errorf("failed to list files, error: %w", err)
}
// do something with the artifact content
for _, f := range files {
log.Info("Processing " + f.Name())
}
return ctrl.Result{}, nil
}
To add the watcher to an existing project, copy the controller and the revision change predicate to your controllers dir:
In your main.go init function, register the Source API schema:
import (
utilruntime "k8s.io/apimachinery/pkg/util/runtime"
clientgoscheme "k8s.io/client-go/kubernetes/scheme"
sourcev1 "github.com/fluxcd/source-controller/api/v1"
)
func init() {
utilruntime.Must(clientgoscheme.AddToScheme(scheme))
utilruntime.Must(sourcev1.AddToScheme(scheme)
// +kubebuilder:scaffold:scheme
}
Start the controller in the main function:
func main() {
if err = (&controllers.GitRepositoryWatcher{
Client: mgr.GetClient(),
HttpRetry: httpRetry,
}).SetupWithManager(mgr); err != nil {
setupLog.Error(err, "unable to create controller", "controller", "GitRepositoryWatcher")
os.Exit(1)
}
}
Note that the watcher depends on Flux runtime and Kubernetes controller-runtime:
require (
github.com/fluxcd/pkg/runtime v0.35.0
sigs.k8s.io/controller-runtime v0.14.6
)
That’s it! Happy hacking!