imikushin/controllers-af

A tiny Go library for building Kubernetes Controllers - As Functions

Controllers AF

A Go library for building Kubernetes Controllers - As Functions

Why

Building Kubernetes controllers is hard. One of the reasons is: it is very hard to write unit-tests for controllers. Why is that? Controllers need to talk to the Kubernetes API all the time, and it takes enormous discipline to mock out these interactions. So, what ends up happening: we don't do it, and our controllers become branching spaghetti monsters.

Enter Controllers AF. It is a tiny library (or micro-framework) built on top of controller-runtime and is designed to do one thing: separate controller logic from interactions with Kubernetes API. Usage section below illustrates how to use it. We also provide a fully functioning example.

Usage

package yourcontroller

import (
	"context"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	ctrl "sigs.k8s.io/controller-runtime"
	"sigs.k8s.io/controller-runtime/pkg/client"
	"sigs.k8s.io/controller-runtime/pkg/source"

	"github.com/imikushin/controllers-af/function"
	"github.com/imikushin/controllers-af/reconciler"

	yourapiv1alpha1 "github.com/your/awesome-controller/api/v1alpha1"
)

func SetupWithManager(mgr ctrl.Manager) error {
	theClient := mgr.GetClient()
	log := ctrl.Log.WithName("controllers").WithName("YourObject")

	yourReconciler := reconciler.New(theClient, log, &yourapiv1alpha1.YourObject{}, ReconcileFun)
	
	return ctrl.NewControllerManagedBy(mgr).For(&yourapiv1alpha1.YourObject{}).Complete(yourReconciler)
}

func ReconcileFun(_ context.Context, object client.Object, getDetails function.GetDetails) (*function.Effects, error) {
	yourObject := object.(*yourapiv1alpha1.YourObject)
	
	yourOtherObjects := getDetails(function.Query{
		Namespace: yourObject.Namespace,
		Type:      &yourapiv1alpha1.YourOtherObjectList{},
		Selector:  metav1.LabelSelectorAsSelector(yourObject.Spec.YourOtherObjectSelector),
	}).(*YourOtherObjectList)
	
	// calculate your effects - no need to talk to the API!

	return &function.Effects{
		Persists: []client.Object{create, or, update, these},
		Deletes: []client.Object{things, toDelete},
	}, nil
}

controllers-af's Issues

logging from within the ReconcileFunc?

Hi, I'm trying out this library for the first time.

What's a good way to get a logger from within the Reconcile callback?

Could I pull one off the context somehow (first function argument)?

occasional error when patching status

My controller logs occasionally show errors like this:

ERROR   controller-runtime.manager.controller.servicedirectory  Reconciler error        {"reconciler group": "connectivity.tanzu.vmware.com", "reconciler kind": "ServiceDirectory", "name": "foo", "namespace": "some-service-provider", "error": "servicedirectories.connectivity.tanzu.vmware.com \"foo\" not found"}
github.com/go-logr/zapr.(*zapLogger).Error
        /home/kokoni/.asdf/installs/golang/1.16.3/packages/pkg/mod/github.com/go-logr/[email protected]/zapr.go:132
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler
        /home/kokoni/.asdf/installs/golang/1.16.3/packages/pkg/mod/sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:302
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem
        /home/kokoni/.asdf/installs/golang/1.16.3/packages/pkg/mod/sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:253
...

When I add various fmt.Errorf() wrapping inside this library, then I see a bit more of where it's coming from:

ERROR   controller-runtime.manager.controller.servicedirectory  Reconciler error        {"reconciler group": "connectivity.tanzu.vmware.com", "reconciler kind": "ServiceDirectory", "name": "foo", "namespace": "some-service-provider", "error": "controllers-af persist: persistObjects patch: status patch: servicedirectories.connectivity.tanzu.vmware.com \"foo\" not found"}

This seems to happen the first time the library tries to patch the status for a resource, but then it retriggers and gets past it.

I haven't had a chance to dig into this too much now, but in case there's an easy/obvious fix, I wanted to report it early.

Thanks!