// when the default revision changes.
type DefaultWatcher interface {
	Run(stopCh <-chan struct{})
	HasSynced() bool
	GetDefault() string
	AddHandler(handler DefaultHandler)
}

// DefaultHandler is a callback for when the default revision changes.
type DefaultHandler func(string)

type defaultWatcher struct {
	revision        string
	defaultRevision string
	handlers        []DefaultHandler

## Upgrade Planning

	"istio.io/istio/pkg/test/framework/config"
)

var _ config.Value = &RevVerMap{}

// RevVerMap maps installed revisions to their Istio versions.
type RevVerMap map[string]IstioVersion

func (rv *RevVerMap) SetConfig(mi any) error {
	m, ok := mi.(config.Map)
	if !ok {
		return fmt.Errorf("revisions map: expected map but got slice")
	}
	out := make(RevVerMap)
	for k := range m {
		version := m.String(k)

```yaml
meshConfig:
  accessLogFile: /dev/stdout
```

#### Revisions

Control plane revisions allow deploying multiple versions of the control plane in the same cluster.
This allows safe [canary upgrades](https://istio.io/latest/docs/setup/upgrade/canary/)

```yaml
revision: my-revision-name

Di Xu <******@****.***> 1532509796 +0800

	defer logRuntime(time.Now(), "Done getting control plane revisions/versions")

	text := ""
	text += fmt.Sprintf("CLI version:\n%s\n\n", version.Info.LongForm())

	revisions := getIstioRevisions(resources)
	istioVersions, proxyVersions := getIstioVersions(ctx, istioNamespace, revisions)
	text += "The following Istio control plane revisions/versions were found in the cluster:\n"
	for rev, ver := range istioVersions {

apiVersion: release-notes/v2
kind: bug-fix
area: istioctl
issue:
  - 45242
releaseNotes:
  - |

				})
			}
		})
}

func verifyRevision(t framework.TestContext, i istioctl.Instance, podName, podNamespace, revision string) {
	t.Helper()
	pcArgs := []string{"pc", "bootstrap", podName, "-n", podNamespace}
	bootstrapConfig, _ := i.InvokeOrFail(t, pcArgs)
	expected := fmt.Sprintf("\"discoveryAddress\": \"istiod-%s.istio-system.svc:15012\"", revision)

}

func NewTagWatcher(client kube.Client, revision string) TagWatcher {
	p := &tagWatcher{
		revision: revision,
	}
	p.queue = controllers.NewQueue("tag", controllers.WithReconciler(func(key types.NamespacedName) error {
		p.notifyHandlers()
		return nil
	}))
	p.webhooks = kclient.NewFiltered[*admissionregistrationv1.MutatingWebhookConfiguration](client, kubetypes.Filter{

	overrideHelpStr = `If true, allow revision tags to be overwritten, otherwise reject revision tag updates that
overwrite existing revision tags.`
	revisionHelpStr = "Control plane revision to reference from a given revision tag"
	tagCreatedStr   = `Revision tag %q created, referencing control plane revision %q. To enable injection using this
revision tag, use 'kubectl label namespace <NAMESPACE> istio.io/rev=%s'
`