# 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.

## Reference

### Design details

Broadly, `istio-cni` accomplishes ambient redirection by instructing ztunnel to set up sockets within the application pod network namespace, where:

- one end of the socket is in the application pod

- [node selector](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#nodeselector)
- [toleration](https://kubernetes.io/docs/concepts/configuration/taint-and-toleration/)
- [affinity and anti-affinity](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#affinity-and-anti-affinity)
- [deployment strategy](https://kubernetes.io/docs/concepts/workloads/controllers/deployment/)

  // controller. If a Job is suspended after creation (i.e. the flag goes from
  // false to true), the Job controller will delete all active Pods associated
  // with this Job. Users must design their workload to gracefully handle this.
  // Suspending a Job will reset the StartTime field of the Job, effectively
  // resetting the ActiveDeadlineSeconds timer too. Defaults to false.
  //
  // +optional

# Istio operator code overview

## Introduction

This document covers primarily the code, with some background on how the design maps to it.
See the
[design doc](https://docs.google.com/document/d/11j9ZtYWNWnxQYnZy8ayZav1FMwTH6F6z6fkDYZ7V298/edit#heading=h.qex63c29z2to)
for a more complete design description. The operator code is divided roughly into five areas:

1. [IstioOperatorSpec API](#istiooperatorspec-api) and related infrastructure, which is expressed as a

  //
  // Valid values are:
  //  "signing", "digital signature", "content commitment",
  //  "key encipherment", "key agreement", "data encipherment",
  //  "cert sign", "crl sign", "encipher only", "decipher only", "any",
  //  "server auth", "client auth",
  //  "code signing", "email protection", "s/mime",
  //  "ipsec end system", "ipsec tunnel", "ipsec user",