This offered performance benefits that were too large to leave on the table, as well as opportunities to tune to our specific needs.

## Configuration protocol

Ztunnel, of course, needs to be dynamically configured in order to make decisions on how it should handle traffic.

![SDS decision flow](docs/sds-flow.svg)

### Default CA Flow through istio-agent

![CA Flow](docs/ca.svg)

A single SDS request from Envoy goes through a few different layers in istio-agent.

// MutatingWebhookConfiguration kubernetes object. This is exposed for
// integration tests only
type MutatingWebhookConfigInfo struct {
	Name     string `json:"name"`
	Revision string `json:"revision"`
	Tag      string `json:"tag,omitempty"`
}

// NsInfo represents namespace related information like pods running there.
// It is used to display data and is exposed for integration tests.
type NsInfo struct {

# Adapted from istio-discovery/templates/mutatingwebhook.yaml
# Removed paths for legacy and default selectors since a revision tag
# is inherently created from a specific revision
{{- $whv := dict
 "revision" .Values.revision
  "injectionPath" .Values.istiodRemote.injectionPath
  "injectionURL" .Values.istiodRemote.injectionURL
  "reinvocationPolicy" .Values.sidecarInjectorWebhook.reinvocationPolicy
  "namespace" .Release.Namespace }}
{{- define "core" }}

                      type: array
                    randomSamplingPercentage:
                      description: Controls the rate at which traffic will be selected
                        for tracing if no prior sampling decision has been made.
                      format: double
                      maximum: 100
                      minimum: 0
                      nullable: true
                      type: number

                      type: array
                    randomSamplingPercentage:
                      description: Controls the rate at which traffic will be selected
                        for tracing if no prior sampling decision has been made.
                      format: double
                      maximum: 100
                      minimum: 0
                      nullable: true
                      type: number

	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'
`

kind: ClusterRoleBinding
metadata:
  name: istiod-clusterrole{{- if not (eq .Values.revision "")}}-{{ .Values.revision }}{{- end }}-{{ .Release.Namespace }}
  labels:
    app: istiod
    release: {{ .Release.Name }}
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: istiod-clusterrole{{- if not (eq .Values.revision "")}}-{{ .Values.revision }}{{- end }}-{{ .Release.Namespace }}
subjects:
  - kind: ServiceAccount

kind: RoleBinding
metadata:
  name: istiod{{- if not (eq .Values.revision "")}}-{{ .Values.revision }}{{- end }}
  namespace: {{ .Values.global.istioNamespace }}
  labels:
    app: istiod
    release: {{ .Release.Name }}
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: istiod{{- if not (eq .Values.revision "")}}-{{ .Values.revision }}{{- end }}
subjects:
  - kind: ServiceAccount

{{- if .Values.global.defaultPodDisruptionBudget.enabled }}
apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: istiod{{- if not (eq .Values.revision "") }}-{{ .Values.revision }}{{- end }}
  namespace: {{ .Release.Namespace }}
  labels:
    app: istiod
    istio.io/rev: {{ .Values.revision | default "default" | quote }}
    install.operator.istio.io/owning-resource: {{ .Values.ownerName | default "unknown" }}