Add "What's new in v2.0?" page

This page is targeted at folks who're already familiar with v1.x and
just want to know what's new.

Signed-off-by: Nic Cope <nicc@rk0n.org>

content/v2.0-preview/_index.md

@@ -15,6 +15,9 @@ Crossplane organizes its documentation into the following sections:
 * [What's Crossplane?]({{<ref "whats-crossplane">}}) introduces Crossplane
   and explains why you should use it.
 
+* [What's New in v2?]({{<ref "whats-new">}}) highlights what's changed in
+  Crossplane v2.
+
 * [Get Started]({{<ref "get-started">}}) explains how to install Crossplane and
   create a control plane.
 

content/v2.0-preview/get-started/_index.md

@@ -1,6 +1,6 @@
 ---
 title: Get Started
-weight: 4
+weight: 40
 description: Get started with Crossplane.
 ---
 

content/v2.0-preview/get-started/get-started-with-managed-resources.md

@@ -36,6 +36,15 @@ This guide requires:
 * An AWS account with permissions to create an S3 storage bucket
 * AWS [access keys](https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-quickstart.html#cli-configure-quickstart-creds)
 
+{{<hint "note">}}
+Only AWS managed resources support the Crossplane v2 preview.
+
+<!-- vale gitlab.FutureTense = NO -->
+Maintainers will update the managed resources for other systems including Azure,
+GCP, Terraform, Helm, GitHub, etc to support Crossplane v2 soon.
+<!-- vale gitlab.FutureTense = YES -->
+{{</hint>}}
+
 ## Install support for the managed resource
 
 Follow these steps to install support for the `Bucket` managed resource:

content/v2.0-preview/whats-new/_index.md

@@ -0,0 +1,236 @@
+---
+title: What's New in v2?
+weight: 4
+description: Learn what's new in the Crossplane v2 preview
+---
+**Crossplane v2 makes Crossplane more useful, more intuitive, and less
+opinionated.**
+
+Crossplane v2 makes three major changes:
+
+* **Composite resources are now namespaced**
+* **Managed resources are now namespaced**
+* **Composition supports any Kubernetes resource**
+
+Despite these major changes, Crossplane v2 is backward compatible with
+Crossplane v1.
+
+```mermaid
+flowchart LR
+  user(User)
+
+  subgraph ns [my-namespace]
+    direction LR
+    xr("App (XR)")
+  	dply("Deployment")
+    svc("Service")
+    rds("RDSInstance (MR)")
+  end
+
+  user --create-->xr
+  xr compose-dply@--compose--> dply
+  xr compose-svc@--compose--> svc
+  xr compose-rds@--compose--> rds
+compose-dply@{animate: true}
+
+compose-dply@{animate: true}
+compose-svc@{animate: true}
+compose-rds@{animate: true}
+```
+
+**Crossplane v2 is better suited to building control planes for applications,
+not just infrastructure.** It removes the need for awkward abstractions like
+claims and provider-kubernetes Objects.
+
+{{<hint "tip">}}
+Most users can upgrade to Crossplane v2 without breaking changes.
+{{</hint>}}
+
+{{<hint "note">}}
+This page assumes you're familiar with Crossplane. New to Crossplane? Read
+[What's Crossplane]({{<ref "whats-crossplane">}}) instead.
+{{</hint>}}
+
+
+## Namespaced composite resources
+
+Crossplane v2 makes composite resources (XRs) namespaced by default.
+
+A namespaced XR can any resource ([not just Crossplane resources](#compose-any-resource))
+in its namespace.
+
+A namespaced XR looks like this:
+
+```yaml
+apiVersion: example.crossplane.io/v1
+kind: App
+metadata:
+  namespace: default
+  name: my-app
+spec:
+  image: nginx
+  crossplane:
+    compositionRef:
+      name: app-kcl
+    compositionRevisionRef:
+      name: app-kcl-41b6efe
+    resourceRefs:
+    - apiVersion: apps/v1
+      kind: Deployment
+      name: my-app-9bj8j
+    - apiVersion: v1
+      kind: Service
+      name: my-app-bflc4
+```
+
+{{<hint "note">}}
+Crossplane v2 moves all an XR's "Crossplane machinery" under `spec.crossplane`.
+This makes it easier for users to tell which fields are important to them, and
+which are just "Crossplane stuff" they can ignore.
+{{</hint>}}
+
+Composite resource definitions (XRDs) now have a `scope` field. The `scope`
+field defaults to `Namespaced` in the new v2alpha1 version of the XRD API.
+
+```yaml
+apiVersion: apiextensions.crossplane.io/v2alpha1
+kind: CompositeResourceDefinition
+metadata:
+  name: apps.example.crossplane.io
+spec:
+  scope: Namespaced
+  group: example.crossplane.io
+  names:
+    kind: App
+    plural: apps
+  versions:
+  - name: v1
+  # Removed for brevity
+```
+
+You can also set the `scope` field to `Cluster` to create a cluster scoped XR. A
+cluster scoped XR can compose any cluster scoped resource. A cluster scoped XR
+can also compose any namespaced resource in any namespace.
+
+With namespaced XRs there's no longer a need for claims. **The new namespaced
+and cluster scoped XRs in Crossplane v2 don't support claims.**
+
+{{<hint "tip">}}
+Crossplane v2 is backward compatible with v1-style XRs.
+
+When you use v1 of the XRD API `scope` defaults to a special `LegacyCluster`
+mode. `LegacyCluster` XRs support claims and don't use `spec.crossplane`.
+{{</hint>}}
+
+## Namespaced managed resources
+
+Crossplane v2 makes all managed resources (MRs) namespaced.
+
+This enables a namespaced XR to compose entirely of namespaced resources -
+whether they're a Crossplane MR like an `RDSInstance`, a Kubernetes resource
+like a `Deployment`, or a third party custom resource like a
+[Cluster API](https://cluster-api.sigs.k8s.io) `Cluster`.
+
+A namespaced MR looks like this:
+
+```yaml
+apiVersion: s3.aws.m.upbound.io/v1beta1
+kind: Bucket
+metadata:
+  namespace: default
+  generateName: my-bucket
+spec:
+  forProvider:
+    region: us-east-2
+```
+
+Namespaced MRs work great with or without composition. Crossplane v2 isn't
+opinionated about using composition and MRs together. Namespaces enable fine
+grained access control over who can create what MRs.
+
+{{<hint "note">}}
+During the Crossplane v2 preview only namespaced AWS managed resources are
+available.
+
+<!-- vale gitlab.FutureTense = NO -->
+Maintainers will update the managed resources for other systems including Azure,
+GCP, Terraform, Helm, GitHub, etc to support namespaced MRs soon.
+<!-- vale gitlab.FutureTense = YES -->
+{{</hint>}}
+
+{{<hint "tip">}}
+Crossplane v2 is backward compatible with v1-style cluster scoped MRs.
+
+<!-- vale gitlab.FutureTense = NO -->
+New provider releases will support both namespaced and cluster scoped MRs.
+Crossplane v2 considers cluster scoped MRs a legacy feature. Crossplane will
+deprecate and remove cluster scoped MRs at a future date.
+<!-- vale gitlab.FutureTense = YES -->
+{{</hint>}}
+
+## Compose any resource
+
+Crossplane v2 isn't opinionated about using composition together with managed
+resources.
+
+You can create a composite resource (XR) that composes any resource, whether
+it's a Crossplane MR like an `RDSInstance`, a Kubernetes resource like a
+`Deployment`, or a third party custom resource like a
+[CloudNativePG](https://cloudnative-pg.io) PostgreSQL `Cluster`.
+
+```mermaid
+flowchart LR
+  user(User)
+
+  subgraph ns [my-namespace]
+    direction LR
+    xr("App (XR)")
+  	dply("Deployment")
+    svc("Service")
+    pg("CloudNativePG Cluster")
+  end
+
+  user --create-->xr
+  xr compose-dply@--compose--> dply
+  xr compose-svc@--compose--> svc
+  xr compose-pg@--compose--> pg
+compose-dply@{animate: true}
+
+compose-dply@{animate: true}
+compose-svc@{animate: true}
+compose-pg@{animate: true}
+```
+
+This opens composition to exciting new use cases - for example building custom
+app models with Crossplane.
+
+## Backward compatibility
+
+Crossplane v2 makes the following breaking changes:
+
+* It removes native patch and transform composition.
+* It removes the `ControllerConfig` type.
+* It removes support for external secret stores.
+
+Crossplane deprecated native patch and transform composition in Crossplane
+v1.17. It's replaced by composition functions.
+
+Crossplane deprecated the `ControllerConfig` type in v1.11. It's replaced by the
+`DeploymentRuntimeConfig` type.
+
+Crossplane added external secret stores in v1.7. External secret stores have
+remained in alpha for over two years and are now unmaintained.
+
+{{<hint "important">}}
+As long as you're not using these deprecated or alpha features, Crossplane v2 is
+backward compatible with Crossplane v1.x.
+{{</hint>}}
+
+<!-- vale gitlab.FutureTense = NO -->
+Crossplane v2 supports legacy v1-style XRs and MRs. Most users will be able to
+upgrade from v1.x to Crossplane v2 without breaking changes.
+
+Existing Compositions will require minor updates to work with Crossplane v2
+style XRs. A migration guide will be available closer to the final release of
+Crossplane v2.
+<!-- vale gitlab.FutureTense = YES -->