controller-utils

README

controller-utils

About this project

This repository contains the controller-utils library which provides utility functions for Open Managed Control Planes projects. It also contains multiple functions and helper structs which are useful for developing k8s controllers and have been found to be copied around from one controller repository to another.

Requirements and Setup

$ go get github.com/openmcp-project/controller-utils@latest

Packages

Clientconfig

The pkg/clientconfig package provides helper functions for creating Kubernetes clients using multiple connection methods. It defines a Config struct that encapsulates a Kubernetes API target and supports various authentication methods like kubeconfig file and a Service Account.

Noteworthy Functions

• GetRESTConfig generates a *rest.Config for interacting with the Kubernetes API. It supports using a kubeconfig string, a kubeconfig file path, a secret reference that contains a kubeconfig file or a Service Account.
• GetClient creates a client.Client for managing Kubernetes resources.

Webhooks

The pkg/init/webhooks provides easy tools to deploy webhook configuration and certificates on a target cluster.

Noteworthy Functions

• GenerateCertificate generates and deploy webhook certificates to the target cluster.
• Install deploys mutating/validating webhook configuration on a target cluster.

CRDs

The pkg/init/crds package allows user to deploy CRDs from yaml files to a target cluster. It uses embed.FS to provide the files for deployment.

collections

The pkg/collections package contains multiple interfaces for collections, modelled after the Java Collections Framework. The only actual implementation currently contained is a LinkedList, which fulfills the List and Queue interfaces.

The package also contains further packages that contain some auxiliary functions for working with slices and maps in golang, e.g. for filtering.

clusters

The pkg/clusters package helps with loading kubeconfigs and creating clients for multiple clusters.

foo := clusters.New("foo") // initializes a new cluster with id 'foo'
foo.RegisterConfigPathFlag(cmd.Flags()) // adds a '--foo-cluster' flag to the flag set for passing in a kubeconfig path
foo.InitializeRESTConfig() // loads the kubeconfig using the 'LoadKubeconfig' function from the 'controller' package
foo.InitializeClient(myScheme) // initializes the 'Client' and 'Cluster' interfaces from the controller-runtime

You can then use the different getter methods for working with the cluster.

conditions

The pkg/conditions package helps with managing condition lists.

The managed condition implementation must satisfy the Condition[T comparable] interface:

type Condition[T comparable] interface {
	GetType() string
	SetType(conType string)
	GetStatus() T
	SetStatus(status T)
	GetLastTransitionTime() time.Time
	SetLastTransitionTime(timestamp time.Time)
	GetReason() string
	SetReason(reason string)
	GetMessage() string
	SetMessage(message string)
}

To manage conditions, use the ConditionUpdater function and pass in a constructor function for your condition implementation and the old list of conditions. The bool argument determines whether old conditions that are not updated remain in the returned list (false) or are removed, so that the returned list contains only the conditions that were touched (true).

updater := conditions.ConditionUpdater(func() conditions.Condition[bool] { return &conImpl{} }, oldCons, false)

Note that the ConditionUpdater stores the current time upon initialization and will set each updated condition's timestamp to this value, if the status of that condition changed as a result of the update. To use a different timestamp, manually overwrite the Now field of the updater.

Use UpdateCondition or UpdateConditionFromTemplate to update a condition:

updater.UpdateCondition("myCondition", true, "newReason", "newMessage")

If all conditions are updated, use the Conditions method to generate the new list of conditions. The originally passed in list of conditions is not modified by the updater. The second return value is true if the updated list of conditions differs from the original one.

updatedCons, changed := updater.Conditions()

For simplicity, all commands can be chained:

updatedCons, changed := conditions.ConditionUpdater(func() conditions.Condition[bool] { return &conImpl{} }, oldCons, false).UpdateCondition("myCondition", true, "newReason", "newMessage").Conditions()

controller

The pkg/controller package contains useful functions for setting up and running k8s controllers.

Noteworthy Functions

• LoadKubeconfig creates a REST config for accessing a k8s cluster. It can be used with a path to a kubeconfig file, or a directory containing files for a trust relationship. When called with an empty path, it returns the in-cluster configuration.
• There are some functions useful for working with annotations and labels, e.g. HasAnnotationWithValue or EnsureLabel.
• There are multiple predefined predicates to help with filtering reconciliation triggers in controllers, e.g. HasAnnotationPredicate or DeletionTimestampChangedPredicate.
• The K8sNameHash function can be used to create a hash that can be used as a name for k8s resources.

logging

This package contains the logging library from the Landscaper controller-utils module.

The library provides a wrapper around logr.Logger, exposing additional helper functions. The original logr.Logger can be retrieved by using the Logr() method. Also, it notices when multiple values are added to the logger with the same key - instead of simply overwriting the previous ones (like logr.Logger does it), it appends the key with a _conflict(x) suffix, where x is the number of times this conflict has occurred.

Noteworthy Functions

• GetLogger() is a singleton-style getter function for a logger.
• There are several FromContext... functions for retrieving a logger from a context.Context object.
• InitFlags(...) can be used to add the configuration flags for this logger to a cobra FlagSet.

testing

This package contains useful functionality to aid with writing tests.

Most notably, the Environment provides a context.Context containing a logger, a k8s fake client, and has helper methods to allow for easy tests of Reconcile methods.

Noteworthy Functions

• Use NewEnvironmentBuilder to construct a simple test environment.
• Environment is a simplicity wrapper around ComplexEnvironment, which can be used for more complex test scenarios which involve more than one cluster and/or reconciler. Use NewComplexEnvironmentBuilder to construct a new ComplexEnvironment.

Examples

Initialize a Environment and use it to check if an object is reconciled successfully:

env := testing.NewEnvironmentBuilder().
  WithFakeClient(nil). // insert your scheme if it differs from default k8s scheme
  WithInitObjectPath("testdata", "test-01").
  WithReconcilerConstructor(func(c client.Client) reconcile.Reconciler {
    return &MyReonciler{
      Client: c,
    }
  }).
  Build()

env.ShouldReconcile(testing.RequestFromStrings("testresource"))

Support, Feedback, Contributing

This project is open to feature requests/suggestions, bug reports etc. via GitHub issues. Contribution and feedback are encouraged and always welcome. For more information about how to contribute, the project structure, as well as additional contribution information, see our Contribution Guidelines.

Security / Disclosure

If you find any bug that may be a security problem, please follow our instructions at in our security policy on how to report it. Please do not create GitHub issues for security-related doubts or problems.

Code of Conduct

We as members, contributors, and leaders pledge to make participation in our community a harassment-free experience for everyone. By participating in this project, you agree to abide by its Code of Conduct at all times.

Licensing

Copyright 2025 SAP SE or an SAP affiliate company and controller-utils contributors. Please see our LICENSE for copyright and license information. Detailed information including third-party components and their licensing/copyright information is available via the REUSE tool.