flux2/rfcs/0006-alternative-suspend-control

RFC-0006 Alternative Suspend Control

Status: provisional

Creation date: 2023-09-20

Last update: 2023-10-10

Summary

This RFC proposes an alternative method to indicate the suspended state of suspendable resources to flux controllers through object metadata. It presents an annotation key that can be used to suspend a resource from reconciliation as an alternative to the .spec.suspend field. It does not address the deprecation of the the .spec.suspend field from the resource apis. This annotation can optionally act as a vehicle for communicating contextual information about the suspended resource to users.

Motivation

The current implementation of suspending a resource from reconciliation uses the .spec.suspend field. A change to this field results in a generation number increase which can be confusing when diffing.

Teams may wish to communicate information about the suspended resource, such as the reason for the suspension, in the object itself.

Goals

The flux reconciliation loop will support recognizing a resource's suspend status based on either the .spec.suspend field or a specific metadata annotation key. The flux cli will similarly recognize this state with get commands and but will only manipulate the annotation key under suspend and resume commands. The flux cli will support optionally setting the suspend metadata annotation value with a user supplied string for a contextual message.

Non-Goals

The deprecation plan for the .spec.suspend field is out of scope for this RFC.

Proposal

Register a flux resource metadata key reconcile.fluxcd.io/suspended with a suspend semantic to be interpreted by controllers and manipulated by the cli. The presence of the annotation key is an alternative to the .spec.suspend: true api field setting when considering if a resource is suspended or not. The annotation key is set by a flux suspend command and removed by a flux resume command. The annotation key value is open for communicating a message or reason for the object's suspension. The value can be set using a --message flag to the suspend command.

User Stories

Suspend/Resume without Generation Roll

Currently when a resource is set to suspended or resumed the .spec.suspend field is mutated which results in a roll of the generation number in the .metadata.generation and fields .status.observedGeneration number. The community believes that the generation change for this reason is not in alignment with gitops principles.

The flux controllers should recognize that a resource is suspended or unsuspended from the presence of a special metadata key -- this key can be added, removed or changed without patching the object and rolling the generation number.

Seeing Suspend State

Users should be able to see the effective suspend state of the resource with a flux get command. The display should mirror what the controllers interpret the suspend state to be. This story is included to capture current functionality that should be preserved.

Suspend with a Reason

Often there is a purpose behind suspending a resource with the flux cli, whether it be during incident response, source manifest cutovers, or various other scenarios. The flux diff command provides a great UX for determining what will change if a suspended resource is resumed, but it doesn't help explain why something is paused or when it would be ok to resume reconciliation. On distributed teams this can become a point of friction as it needs to be communicated among group stakeholders.

Flux users should have a way to succinctly signal to other users why a resource is suspended on the resource itself.

Alternatives

More .spec

The existing .spec.suspend could be expanded with fields for the above semantics. This would drive more generation number changes and would require a change to the apis.

Design Details

Implementing this RFC would involve the controllers and the cli.

This feature would create an alternate path to suspending an object and would not violate the current apis.

Common

The reconcile.fluxcd.io/suspended annotation key string and a getter function would be made avaiable for controllers the cli to recognize and manipulate the suspend object metadata.

# github.com/fluxcd/pkg/apis/meta


// SuspendAnnotation is the annotation used to indicate an object is suspended and optionally to store metadata about why a resource
// was set to suspended.
const SuspendedAnnotation string = "reconcile.fluxcd.io/suspended"

// SuspendAnnotationValue returns a value for the suspended annotation, which can be used to detect
// changes; and, a boolean indicating whether the annotation was set.
func SuspendedAnnotationValue(annotations map[string]string) (string, bool) {
	suspend, ok := annotations[SuspendedAnnotation]
	return suspend, ok
}

// SetSuspendedAnnotation sets a suspend key with a supplied string value in an object's metadata annotations
func SetSuspendedAnnotation(annotations *map[string]string, token string) {
	if annotations == nil {
		annotations = &map[string]string{}
	}
	if token != "" {
		(*annotations)[SuspendedAnnotation] = token
	} else {
		(*annotations)[SuspendedAnnotation] = "true"
	}
}

// UnsetSuspendedAnnotation removes a suspend key from an object's metadata annotations
func UnsetSuspendedAnnotation(annotations *map[string]string) {
	delete(*annotations, SuspendedAnnotation)
}

An event predicate would skip attempting to reconcile a resource with the suspend annotation set.

# github.com/fluxcd/pkg/apis/predicates

# suspended.go

// Update implements the default UpdateEvent filter for filtering by meta.SuspendedAnnotation existence
func (SuspendedPredicate) Update(e event.UpdateEvent) bool {
	if e.ObjectOld == nil || e.ObjectNew == nil {
		return false
	}

	if _, ok := metav1.SuspendedAnnotationValue(e.ObjectNew.GetAnnotations()); !ok {
		return true
	}
	return false
}

Controllers

Flux controllers would skip reconciling a resource based on an OR of (1) the api .spec.suspend and (2) the existence of the suspend metadata annotation key.

# github.com/fluxcd/kustomize-controller/api/v1
# kustomization_types.go

// IsSuspended returns the effective suspend state of the object.
func (in Kustomization) IsSuspended() bool {
	if in.Spec.Suspend {
		return true
	}
	if _, ok := meta.SuspendedAnnotationValue(in.Annotations); ok {
		return true
	}
	return false
}

# github.com/fluxcd/kustomize-controller/controller
# kustomization_controller.go

// Skip reconciliation if the object is suspended.
// if obj.Spec.Suspend {  // no longer using `.spec.suspend` directly
if obj.Status.IsSuspended {
    log.Info("Reconciliation is suspended for this object")
    return ctrl.Result{}, nil
}

cli

The flux cli would recognize the suspend state from the suspend object status.

# github.com/fluxcd/flux2/main

# get_source_git.go

func (a *gitRepositoryListAdapter) summariseItem(i int, includeNamespace bool, includeKind bool) []string {
	...
    return append(nameColumns(&item, includeNamespace, includeKind),
    //    revision, strings.Title(strconv.FormatBool(item.Spec.Suspend)), status, msg)
        revision, strings.Title(strconv.FormatBool(item.IsSuspended)), status, msg)
}

The flux cli would manipulate the suspend metadata but forgo toggling the .spec.suspend setting. An optional --message|-m flag would support setting the suspended annotation value to a user-specified string.

# github.com/fluxcd/flux2/main

# suspend.go

type SuspendFlags struct {
    ...
    message string
}

func init() {
    ...
    suspendCmd.PersistentFlags().StringVarP(&suspendArgs.message, "message", "m", "",
		"set a message about why the resource is suspended, the message will show up under the reconcile.fluxcd.io/suspended annotation")
    ...
}

type suspendable interface {
    ...
    // setSuspended()
    setSuspended(message string)
}

type suspendCommand struct {
    ...
    // obj.setSuspended()
    obj.setSuspended(suspendArgs.message)
}

# suspend_helmrelease.go

func (obj helmReleaseAdapter) isSuspended() bool {
	return obj.HelmRelease.IsSuspended()                               // use the resource api spec method
}

func (obj helmReleaseAdapter) setSuspended(message string) {
    meta.SetSuspendedAnnotation(&obj.HelmRelease.Annotations, message) // use the common annotation setter
}

# resume_helmrelease.go

func (obj helmReleaseAdapter) setUnsuspended() {
    meta.UnsetSuspendedAnnotation(&obj.HelmRelease.Annotations)        // use the common annotation unsetter
}

Metrics

Custom metrics can be configured under kube-state-metrics using the object metadata annotation path.

- name: "resource_info"
  help: "The current state of a GitOps Toolkit resource."
  each:
    type: Info
    info:
    labelsFromPath:
      name: [metadata, name]
  labelsFromPath:
    ...
    suspendedAnnotation: [ metadata, annotations, reconcile.fluxcd.io/suspended ]

Implementation History

tbd