8.8 KiB
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.
// 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](https://fluxcd.io/flux/monitoring/custom-metrics/#adding-custom-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