* Users may have external CA setups that pre-configure certificates.
* The CaClient can use JWT token for the initial setup, then switch to mTLS certificates.

Note that `OUTPUT_CERTS` can be used to refresh certificates using previously provisioned certificates, by configuring
the ca client to use certificates written to the same directory we have configured them to be written to.

## Authentication

  //
  //   1. Old signer that is unaware of the field (such as the in-tree
  //      implementations prior to v1.22)
  //   2. Signer whose configured maximum is shorter than the requested duration
  //   3. Signer whose configured minimum is longer than the requested duration
  //
  // The minimum valid value for expirationSeconds is 600, i.e. 10 minutes.
  //
  // +optional

and a different team may maintain the control plane components (which are highly security sensitive).

The install is organized in 'environments' - each environment consists of a set of components
in different namespaces that are configured to work together. Regardless of 'environment',
workloads can talk with each other and obey the Istio configuration resources, but each environment
can use different Istio versions and different configuration defaults.

# Port and basic host configuration

In order to configure the Service object, the install/upgrade needs to provide a list of all ports.
In the past, this was done when installing/upgrading full istio, and involved some duplication - ports configured
both in upgrade, Gateway and VirtualService.

- In ambient mode, the CNI plugin does not configure any networking, but is only responsible for synchronously pushing new pod events back up to an ambient watch server which runs as part of the Istio CNI node agent. The ambient server will find the pod netns and configure networking inside that pod via iptables. The ambient server will additionally watch enabled namespaces, and enroll already-started-but-newly-enrolled...

### Examples

#### Configuring mesh configuration settings

Any [Mesh Config](https://istio.io/latest/docs/reference/config/istio.mesh.v1alpha1/) options can be configured like below:

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

#### Revisions

Control plane revisions allow deploying multiple versions of the control plane in the same cluster.

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.
For this purpose, we chose to use xDS transport protocol due to our expertise and existing infrastructure, and because the protocol is well suited to our needs.

  // +optional
  optional string evaluationError = 3;
}

// SubjectRulesReviewStatus contains the result of a rules check. This check can be incomplete depending on
// the set of authorizers the server is configured with and any errors experienced during evaluation.
// Because authorization rules are additive, if a rule appears in a list it's safe to assume the subject has that permission,
// even if that list is incomplete.

  // An empty or nil nodeSelector selects all nodes.
  // This field is immutable.
  // +optional
  optional k8s.io.api.core.v1.NodeSelector nodeSelector = 1;

  // perNodeHostBits defines the number of host bits to be configured per node.
  // A subnet mask determines how much of the address is used for network bits
  // and host bits. For example an IPv4 address of 192.168.0.0/24, splits the

  //
  //   1. Old signer that is unaware of the field (such as the in-tree
  //      implementations prior to v1.22)
  //   2. Signer whose configured maximum is shorter than the requested duration
  //   3. Signer whose configured minimum is longer than the requested duration
  //
  // The minimum valid value for expirationSeconds is 600, i.e. 10 minutes.
  //
  // +optional