Add proposal for Carvel Packages

proposals/xxxx_carvel-package/README.md

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+---
+title: "Carvel Package Management for Pinniped"
+authors: [ "@benjaminapetersen" ]
+status: "in-review"
+sponsor: [ "@cfryanr", "@joshuatcasey" ]
+approval_date: ""
+---
+
+*Disclaimer*: Proposals are point-in-time designs and decisions.
+Once approved and implemented, they become historical documents.
+If you are reading an old proposal, please be aware that the
+features described herein might have continued to evolve since.
+
+# Carvel Package Management for Pinniped
+
+## Problem Statement
+
+There are a number of tools available to the Kubernetes ecosystem for deploying complex software 
+to a Kubernetes cluster.  The Carvel toolchain provides a set of APIs, Custom Resources and CLI tools
+that can aid a user in the configuration and lifecycle management of software deployed to a cluster.
+We should enhance our deployment options by providing Carvel Packages that may be installed on a cluster
+configured with `kapp-controller` to manage the software on the cluster. 
+
+## How Pinniped Works Today (as of version v0.25.0)
+
+The `./deploy` directory in the root of the Pinniped repository contains a set of `ytt` templates
+that:
+- Are pre-rendered into installable templates listed with each Pinniped relese:
+  - [v0.25.0](https://github.com/vmware-tanzu/pinniped/releases/tag/v0.25.0)
+- Can optionally be customized and rendered by a consumer of the Pinniped project by cloning down
+  the github repository, making changes to the `values.yaml` file and then rendered via `ytt`.
+
+## Terminology / Concepts
+
+- `Carvel` is an open-source project that provides tools for managing software build, configuration
+   and deployment on a Kubernetes cluster.  For more information [read the Carvel docs](https://carvel.dev/).
+- `kapp` is a Carvel provided CLI tool for deploying software onto a Kubernetes cluster. See 
+   [the docs](https://carvel.dev/kapp/) for more information.
+- `imgpkg` is a Carvel provided CLI tool that provides a mechanism for collecting configuration and 
+   OCI images into a bundle that can be deployed on a cluster.
+- `kapp-controller` is a server side component managing software in the form of Carvel `App`s delivered
+   via Carvel `Package`s. See [the docs](https://carvel.dev/kapp-controller/) for more information.
+- `PackageRepository` is a custom resource that configures `kapp-controller` with a set of 
+  `Package`s on a cluster.  See [the docs](https://carvel.dev/kapp-controller/docs/v0.47.x/packaging/#package-repository)
+   for more information.
+- `Package` is a custom resource that represents configuration in the form of metadata and OCI images
+   that may be used to deliver software onto a Kuberentes cluster. See [the docs](https://carvel.dev/kapp-controller/docs/v0.47.x/packaging/#package)
+   for more information. 
+- `PackageMetadata` is a custom resource describing attributes for a `Package`.  See [the docs](https://carvel.dev/kapp-controller/docs/v0.47.x/packaging/#package-metadata)
+   for more information.
+
+## Proposal
+
+Allow Pinniped to be deployed onto a Kuberentes cluster through the mechanism of two Carvel `Packages`,
+a Supervisor and a Concierge package. These may be delivered via a `PackageRepository` resource. 
+
+### Goals and Non-goals
+
+Goals
+- Provide an additional deployment option to deliver Pinniped software to a Kubernetes cluster
+  in the form of the `Package` apis provided by the Carvel toolchain.
+
+Non-Goals
+- Provide additional deployment alternatives, such as official Helm charts
+
+#### API Changes
+
+No changes or additions to Pinniped APIs, this proposal represents a second, alternative 
+method for deployment utilising Carvel APIs.  
+
+#### Upgrades
+
+Upgrading Pinniped via the Carvel Package mechanism will look something like this:
+
+- We deliver a `PackageRepository` that lists:
+  - Pinniped `Supervisor` package at a number of versions (ex: 0.23.0,0.24.0,0.25.0, etc)
+  - Pinniped `Concierge` package at a number of versions (ex: 0.23.0,0.24.0,0.25.0, etc)
+- The user installs the Pinniped `PackageRepository`.
+- The user creates:
+  - A `Supervisor` and `Concierge` `PackageInstall` Custom Resource (and `Secret`) with the following:
+```yaml
+spec:  
+  packageRef:
+    refName: "supervisor.pinniped.dev"
+    versionSelection:
+      # - Constraints control the version and upgrades of the package
+      #   if the constraint is pinned to a specific version, then only 
+      #   that version is installed on the cluster
+      # - If the PackageResource no longer serves a version that matches
+      #   the constraint, then the PackageInstall will enter an error state
+      #   until the constraint is updated      
+      constraints: "0.25.0"  
+      # - Alternatively, a constraint can be based on a semver range and can 
+      #   control automatic updates.  
+      constraints: ">0.25.0"  
+```
+
+#### Tests
+
+Our current integration test suite uses the `./deploy` directory to deploy Pinniped onto a 
+variety of clusters.  We should continue to test this for the majority of users who do not 
+integrate with Carvel.  In addition, we should update at least 1 of our tests to make use of 
+the new `Package` mechanism to ensure it functions correctly.  
+
+Optionally we can:
+
+- Change a single test to deploy via the `Package` mechanism
+- Change several tests to deploy via the `Package` mechanism
+- Provide a flag to our `./prepare-for-integration-test.sh` and cycle all of our tests,
+  perhaps randomly back and forth between the simple deploy and the Package deploy.
+
+#### New Dependencies
+
+The Carvel toolset is not strickly a dependency for Pinniped itself.  This proposal is an 
+optional method for delivering the Pinniped software to a kubernetes cluster.  Therefore, `kapp`, 
+`kapp-controller`, and the custom resources such as `PackageRepository`, `Package`, `PackageMetadata`,
+`PackageInstall` as well as `imgpkg`, `vendir` and `ytt` are all optional dependencies for a 
+consumer of Pinniped.
+
+#### Performance Considerations
+
+None.  It is up to the user to determine if the adoption of the Carvel toolset is the 
+correct decision for their application lifecycle needs.
+
+#### Observability Considerations
+
+`Package`, `App` and `PackageInstall` custom resources contain a `status` field like many 
+Kubernetes resources.  These are thoroughly detailed with relevant bits of information that may 
+aid the user in understanding the state of their applications.  For example, a Carvel `App` Custom Resource
+(disambiguation, a Carvel `app` (lowercase) from `kapp` vs an `App` (uppercase) from `kapp-controller` are
+entirely different resources) contains a detailed status referencing all resources owned by the `App`. This
+is very helpful when attempting to understand the state of a complex multi-component application.
+
+#### Security Considerations
+
+Carvel is a toolset separate from Pinniped.  This feature is optional, users who choose to use 
+Carvel should assess Carvel for its risks and treadeoffs. 
+
+#### Usability Considerations
+
+As of today the `./deploy` directory of Pinniped is implemented via the use of a subset of the 
+Carvel toolchain, namely, `ytt`.  However, it is implemented in such a way that consumers of Pinniped
+have choice, they may opt-in to the use of the Carvel toolchain, or simply `kubectl apply -f` our 
+pre-rendered yaml files, there is no requirement to use the Carvel toolchain.
+
+This feature serves the community users who have deeply adopted Carvel into their management, such that
+`kapp-controller` is installed on their cluster and used to manage software lifecycle.
+
+#### Documentation Considerations
+
+This design doc serves as an announcement that the feature will be implemented.
+It would be helpful to provide a blog post describing how the feature was validated.
+Also include in release notes.
+
+#### Other Approaches Considered
+
+None.
+
+## Open Questions
+
+A list of questions that need to be answered.
+
+## Answered Questions 
+
+## Implementation Plan
+
+## Implementation PRs
+
+* TBD