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Add proposal for Carvel Packages

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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Once approved and implemented, they become historical documents.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