KEP: Add kubectl plugin manager (krew)

keps/NEXT_KEP_NUMBER

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keps/sig-cli/0014-krew.md

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+---
+kep-number: 14
+title: Krew
+authors:
+  - "@lbb"
+owning-sig: sig-cli
+participating-sigs:
+  - sig-cli
+reviewers:
+  - TBD
+  - "@pwittroc"
+approvers:
+  - "@pwittroc"
+editor: lbb
+creation-date: 2018-07-03
+last-updated: yyyy-mm-dd
+status: provisional
+see-also:
+  - n/a
+replaces:
+  - n/a
+superseded-by:
+  - n/a
+---
+
+# Krew
+
+## Table of Contents
+* [Krew](#krew)
+  * [Table of Contents](#table-of-contents)
+  * [Summary](#summary)
+  * [Motivation](#motivation)
+    * [Discoverability](#discoverability)
+    * [Cross-platform Packaging](#cross-platform-packaging)
+    * [Lifecycle management](#lifecycle-management)
+    * [Goals](#goals)
+    * [Non-Goals](#non-goals)
+  * [Proposal](#proposal)
+      * [Capabilities](#capabilities)
+    * [Scenarios (standalone only)](#scenarios-standalone-only)
+    * [Scenarios](#scenarios)
+    * [UX and CLI Flow](#ux-and-cli-flow)
+    * [Implementation Details/Notes/Constraints](#implementation-detailsnotesconstraints-optional)
+    * [Risks](#risks)
+  * [Graduation Criteria](#graduation-criteria)
+  * [Implementation History](#implementation-history)
+  * [Drawbacks](#drawbacks)
+
+## Summary
+
+krew is a package manager for the kubectl plugin system. krew introduces a way
+to handle kubectl plugin management and discovery.
+
+## Motivation
+
+The kubectl plugin system allows users to extend kubectl by placing extension
+executables in a plugin directory. This allows new subcommands and subcommand
+trees to be added in the kubectl CLI interface under `kubectl plugin <NAME>`.
+This has the following user friction:
+
+* Users need to manually download and manage plugins to ~/.kube/plugins and
+  keep them up to date
+* Users need to be aware of the installation requirements and instructions of
+  each plugin
+
+Currently, there are no unified distribution methods for kubectl plugins.
+This has several disadvantages:
+
+### Discoverability
+
+Available kubectl plugins are not easily discoverable and searchable.
+
+### Cross-platform Packaging
+
+Plugins need to be packaged separately different OS and distros.
+Often, plugin maintainers do not do this.
+
+### Lifecycle management 
+
+Often installation is done through manually downloading a zip and placing
+it under ~/.kube/plugins. This is an unpleasant experience to the user
+especially when it comes to updating the plugins,
+or when a user deletes ~/.kube.
+
+---
+
+Those disadvantages will lead to slow the adoption rate of kubectl plugins.
+krew will be a plugin manager able to solve all of the named issues. 
+
+### Goals
+
+
+* Install, uninstall and update plugins
+* Discovery of plugins
+* Giving developers a platform to contribute their plugins to
+* Build repository platform for contributors (i.e brew formulas approach)
+* Allow multiple plugin index sources
+* (only for standalone) Self hosting: krew installation doesn't require a
+  package manager: it can upgrade itself 
+
+### Non-Goals
+
+* Dependency management of libraries
+* Plugins are user facing programs, they should not depend on each other.
+  They have environment requirements like curl or git.
+  Krew is not responsible to cover external dependency,
+  program and environment setup like apt,
+  brew or dnf. The user will be informed to take action.
+* Complete integration with various download sources like “hg://” or “samba://”
+* kubectl version compatibility management
+
+
+## Proposal
+
+#### Capabilities
+
+Note: This proposal has already been implemented in
+`github.com/GoogleContainerTools/krew` as a proof of concept.
+The goal is to move it into kubectl.
+
+Define a new meta config format called plugin manifest
+(stored in the index under: <plugin-name>.yaml)
+
+
+### Scenarios (standalone only)
+
+* User wants to install krew. They can run one `curl` command to install the
+  plugin manager, the plugin manager should then be able to function properly.
+
+### Scenarios
+
+* User wants to install and update a plugin.
+  They use the search to discover plugins `kubectl plugin search foo`.
+  Every plugin displays a short description of its purpose.
+  They find the right plugin and install it with the install command.
+  Using the update command them can update all installed plugins to it
+  latest version. 
+* User moves to a new machine and wants to reinstall all their plugins.
+  They can copy the declarative plugin list. This file contains all plugins that
+  were requested by the user to be installed. They have to copy it to the new
+  installation and run an update. There will be a command for exporting and
+  importing depots.
+* Developer wants to make his plugin discoverable by others.
+  They provide a link to the whole plugin as a compressed file under a public
+  URL. (Github provides any commit/tag as .tar.gz automatically.)
+  Afterwards the developer creates a PR against the index repository with a new
+  meta description file. This file contains the download url, download hash,
+  plugin version and description and tags. Meta descriptions are used by the
+  plugin manager to discover and manage plugins.
+* Developer wants to update their plugin and make those changes public.
+  They create a new PR against the index repository updating their plugin meta
+  description file. 
+
+### UX and CLI Flow 
+
+```text
+# Update and fetch plugin index.
+$ kubectl plugin update
+
+# Search for plugins
+$ kubectl plugin search servicecat
+service-catalog     Consume services in Kubernetes using the Open S... available
+service-cat-viewer  Show ASCII cat picture for every Service format... installed  
+service-catalog-gke A helper utility for discovering GKE services l... available
+
+$ kubectl plugin info service-cat-viewer
+DESCRIPTION: Show ASCII cat picture for every Service formatet ISO-11801
+URL: https://github.com/oscar-kitty/viewer.git
+
+CAVEATS:
+This plugin needs the following programs:
+* fzf
+* jq
+
+For a better user experience:
+  export $TERM=vt220
+
+# Install the plugin.
+$ kubectl plugin install service-cat-viewer
+Installation (1/1): service-cat-viewer
+Downloading https://github.com/oscar-kitty/viewer.git
+Progress: 100%
+Done!
+
+Plugin Caveats:
+  This plugin needs the following programs:
+  * fzf
+  * jq
+
+  For a better user experience:
+    export $TERM=vt220
+
+# Update all plugins and index
+$ kubectl plugin upgrade
+
+# Update specific plugins
+$ kubectl plugin upgrade foo bar
+
+# uninstall plugin
+$ kubectl plugin remove aws-cat-viewer
+
+# Store the list of installed plugins
+$ kubectl plugin list > deposit.txt
+
+# On a new machine load the plugin list
+$ kubectl plugin install < deposit.txt
+... [Plugin installation output] ...
+```
+
+### Implementation Details/Notes/Constraints
+
+krew has already been implemented in the `github.com/GoogleContainerTools/krew`
+repo, and should be moved to a separate repo for the sub project.
+krew was initially developed as its own cli, however once it has matured,
+it should be published as a subcommand of kubectl or as a statically linked
+plugin. It should also be more tightly integrated with apply.
+
+### Risks
+The index repository needs some form of governance to prevent malicious plugins. 
+
+## Graduation Criteria
+* Dogfood krew by either:
+  * moving one or more of the cncf clis to it (i.e helm)
+  * getting user feedback from one or more mid or large application deployments
+    using krew.
+* Publish krew as a subcommand of kubectl.
+
+
+## Implementation History
+krew was implemented in the `github.com/GoogleContainerTools/krew` repo before
+subprojects became a first class thing in Kubernetes. The code has been fully
+implemented, but it must be moved to a proper location.
+
+## Drawbacks
+
+Implementing krew and growing the ecosystem can hold back the git-style plugin
+approach.