## PeerAuthentication and ztunnel

This document provides an overview of the architecture and design decisions around Ztunnel, the node-proxy component in ambient mode.

## Background and motivation

Motivations to implement ztunnel generally came from two areas.

First, and most importantly, it serves as a means to implement the real goal: waypoints.
For various reasons outside the scope of this document, there is a desire to move from a sidecar based architecture to a "remote proxy" architecture.

message MutatingWebhookConfiguration {
  // Standard object metadata; More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata.
  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.ObjectMeta metadata = 1;

  // Webhooks is a list of webhooks and the affected resources and operations.
  // +optional

  // +required
  optional string message = 6;
}

// A list of StorageVersions.
message StorageVersionList {
  // Standard list metadata.
  // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.ListMeta metadata = 1;

  // Items holds a list of StorageVersion
  repeated StorageVersion items = 2;
}

message ValidatingAdmissionPolicy {
  // Standard object metadata; More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata.
  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.ObjectMeta metadata = 1;

  // Specification of the desired behavior of the ValidatingAdmissionPolicy.

@Deprecated(since = "4.0.0")
public class Os {

    /**
     * The OS Name.
     */
    public static final String OS_NAME = System.getProperty("os.name").toLowerCase(Locale.ENGLISH);

    /**
     * The OA architecture.
     */
    public static final String OS_ARCH = System.getProperty("os.arch").toLowerCase(Locale.ENGLISH);

    /**
     * The OS version.
     */

# Controllers

Istio has a variety of [controllers](https://kubernetes.io/docs/concepts/architecture/controller/), which basically watch some inputs and do something.
This can be reading from Kubernetes and writing other objects back, writing to proxies over XDS, etc.

Unfortunately, writing controllers is very error prone, even for seemingly simple cases.
To work around this, Istio has a variety of abstractions meant to make writing controllers easier.

## Clients

			{
				"parallelizationMethod":{
					"name":"TeamCityParallelTests",
					"numberOfBatches":1
				},
				"subprojects":[
					"kotlin-dsl-integ-tests",
					"precondition-tester",
					"architecture-test",
					"docs",
					"file-watching",
					"toolchains-jvm",
					"execution",
					"resources-http",
					"internal-performance-testing",
					"internal-integ-testing",

   *     using it, it is probably not doing what you want.
   */
  @Deprecated
  JAVA_EXT_DIRS("java.ext.dirs"),

  /** Operating system name. */
  OS_NAME("os.name"),

  /** Operating system architecture. */
  OS_ARCH("os.arch"),

  /** Operating system version. */
  OS_VERSION("os.version"),

  /** File separator ("/" on UNIX). */
  FILE_SEPARATOR("file.separator"),

  // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.ObjectMeta metadata = 1;

  // spec is the specification for the behaviour of the autoscaler.
  // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status.
  // +optional