Admin overview doc

docs/versioned/admin/admin-overview.md

@@ -0,0 +1,13 @@
+---
+audience: administrator
+components:
+  - serving
+  - eventing
+function: reference
+---
+# Overview
+
+This page provides guidance for administrators on how to manage Knative on an existing Kubernetes cluster.
+
+## The Knative model
+

docs/versioned/install/README.md

@@ -8,24 +8,61 @@ function: reference
 
 # Installing Knative
 
-There are three installation methods to install Knative:
+This page provides guidance for Kubernetes administrators on how to install Knative on an existing Kubernetes cluster. Knative consists of the Serving and Eventing components and the CLI client tools `kn` and `func`.
 
-- A quickstart experience on a local computer only by using a preconfigured extension.
-- A YAML installation suitable for production use.
-- A Knative Operator installation suitable for production use.
+If you just want to understand the functionality of Knative at this time, install the Quickstart as described in the [Installation roadmap](#installation-roadmap).
 
-A Knative installation is composed of the Serving and Eventing components. The quickstart implements both. The YAML and Knative Operator installations provide options to install either or both.
+The installation assumes you, as a Kubernetes administrator, are familiar with the following:
+
+- Kubernetes and Kubernetes administration.
+- The `kubectl` CLI tool. You can use existing Kubernetes management tools (policy, quota, etc) to manage Knative workloads.
+- Using cluster-admin permissions or equivalent to to install software and manage resources in all clusters in the namespace. For information about permissions, see [Using RBAC Authorization](https://kubernetes.io/docs/reference/access-authn-authz/rbac/AC).
+- Familiarity with Cloud Native Computing Foundation (CNCF) projects such as Prometheus, Istio, and Strimzi, many of which can be used alongside Knative, is recommended.
+
+To simplify Knative installation and administration, you can use the Knative Operator with the Knative `kn` CLI tool, but they are not required. Essentially, Knative aims to extend Kubernetes, and build on existing capabilities where feasible.
+
+Knative has three components: Eventing, Serving, and Functions. Serving and Eventing are installed into clusters. Functions is not installed into clusters because it is operated by the client `func` CLI tool.
+
+Serving and Eventing support multiple underlying transports plugins within the same cluster. Serving supports pods with pluggable network ingress routes, and Eventing supports pods with pluggable message transports (e.g. Kafka, RabbitMQ).
+
+Knative has default lightweight messaging implementation if you don't already have a solution. Knative also has Kourier, a default lightweight HTTP routing implementation, if you don't already have an ingress that meets the requirements.
 
 Supported platforms are Linux, MacOS, and Windows.
 
+You can install Knative in the following ways:
+
+- Use a [YAML-based installation](/install/yaml-install/README.md) with `kubectl`.
+
+    This option is the most useful if you're using delivery solutions such as Flux or ArgoCD to apply manifests checked into a Git repository. This is the lowest common denominator approach, giving you granular control of the process and resource definitions.
+
+- Install the [Knative Operator](/install/operator/knative-with-operators.md) using Manifests or Helm, and then use `kubectl` to install Knative components.
+
+    This option alleviates complexity by using the Knative Operator, while still enabling purpose-built manageability using popular tools. It also gives you a separation of the core Knative application definition and the ConfigMap and other changes you make.
+
+- Install the [Knative Operator CLI plugin](/install/operator/knative-with-operator-cli.md) and install the Knative Operator and the Knative CLI `kn` to  Knative components.
+
+    This is the easiest install option and suitable for using if customization is not a concern.
+
+The following table summarizes these installation options.
+
+| Install option | Resources | kubectl CLI | kn CLI |
+| --- | --- | --- | --- |
+| YAML-based | All YAML prepared | Install components | not used |
+| Knative Operator | Install Knative Operator using Manifests or Helm |Install components | not used |
+| Knative Operator | Install Knative Operator CLI plugin | not used | Install components |
+
+For details, see [YAML and Knative Operator installations compared](#yaml-and-knative-operator-installations-compared).
+
+Knative supports subsequent installs after the initial installation, you so your initial choices don't lock you in. For example, you can migrate from one message transport or network ingress to another without losing messages.
+
 ## Installation roadmap
 
-Use the following table to evaluate your installation method.
+Use the following table to evaluate your installation method. If you just want to get an understanding of Knative functionality at this time, install the quickstart.
 
 |  | Quickstart | YAML | Knative Operator |
 | --- | --- | --- | --- |
 | Purpose  | local   | production     | production  |
-| Kubernetes | local deployment of kind or Minikube | existing deployment | existing deployment  |
+| Kubernetes deployment | local, either `kind` or `Minikube` | existing  | existing  |
 | Hardware | 3 CPU, 3 GB RAM | One node: 6 CPUs, 6 GB memory, 30 GB disk storage.<br>Multiple nodes: 2 CPUs each, 4 GB memory, 20 GB disk storage.   | same as YAML |
 
 Use the following steps to install Knative depending on your installation method.
@@ -55,6 +92,54 @@ System requirements provided are recommendations only. The requirements for your
 
 For a list of commercial Knative products, see [Knative offerings](knative-offerings.md).
 
+## YAML and Knative Operator installations compared
+
+You install Knative using YAML files and other resources either aided or not by the Knative Operator. The Knative Operator is a custom controller that extends the Kubernetes API to install Knative components. It allows you to automate applying the content, along with patching the contents to customize them. You install the Knative Operator either by using the Knative CLI Operator Plugin or by using KS8 Manifests or by Helm.
+
+Here are the considerations for installing using YAML or the Knative Operator:
+
+| YAML-based install | Knative Operator install|
+| --- | --- |
+| You can see exactly what you get. | You specify choices at a higher level. |
+| You can adjust any parameters by editing them directly. | Not every setting is exposed. |
+| If you make changes, you have to keep track of what you changed when you want to upgrade. | It's easy to separate your customizations from the base installation. |
+| Version and audit control as YAML files are stored in a GitHub repository.| No version or audit control. |
+
+## Extensibility plugins
+
+Knative utilizes existing infrastructure already have installed on your cluster, while standardizing the developer-facing interface between similar components. You can add the following resources to extend the cluster infrastructure.
+
+Networking plugins:
+
+- Kourier
+    Data management from [Kore Technologies](https://koretech.com) with has a internal no-dependency option.
+- Istio
+    Service mesh from [Istio](https://istio.io). See [Installing Istio for Knative](installing-istio.md)
+- Courier
+    General-purpose ingress.
+- Gateway API
+    Kubernetes [Gateway API](https://kubernetes.io/docs/concepts/services-networking/gateway/) (beta)
+
+Messaging plugins:
+
+- Kafka
+    Distributed event streaming platform from [Apache Kafka](https://kafka.apache.org). In-order, high-thoughput but moderate complexity. See [Install Kafka for Knative](/install/eventing/kafka-install.md).
+- RabbitMQ
+    A messaging and streaming broker from [RabbitMQ](https://www.rabbitmq.com). In-order, moderate throughput and complexity. See [Install RabbitMQ for Knative](/install/eventing/rabbitmq-install.md)
+- NATS
+    An event streaming platform from [NATS](https://nats.io). Low complexity.
+
+Knative has an in-memory and internal no-dependency messaging option.
+
+## Integration plugins
+
+These plugins facilitate Knative operations.
+
+- cert-manager
+    For requesting TLS certificates in secure HTTPS connections, see [Install cert-manager](/install/installing-cert-manager.md).
+- Backstage
+    Plugins for handling Knative backends. See [Installing backstage plugins](/install/installing-backstage-plugins.md).
+
 ## Installation resources
 
 Use the following links to maintain your installations.