Chart v3 User Stories

This document contains user stories for Helm3 Charts. User stories provide guidance, but are not necessarily a list of requirements.

All stories in this document are implicitly prefaced with "As a Chart Developer..." and are of the form "As a ROLE I want TASK so that GOAL.

General

• I want to re-use Helm 2 charts so that I don't have to rebuild the same thing
• I want to create charts the Helm 2 way so that I can continue developing the way I have been
• I do not want to have to understand all the details of every subchart I use so that I can compose complex applications quickly

Extensions/Lua

These all assume a Lua engine, and describe things to be done in Lua scripts. See the current events and chart structure proposals

Values

• I want programmatic access to subchart values so that I can access defaults
• I want access to modify subchart values so that I can explicitly set a value for a subchart
• I want late access to a subchart's values so that I can discover any values that a subchart's scripts computed
• I want to use Lua to validate values before templates are rendered so that I can alert users to unexpected values before install fails
• I want to use Lua to modify values in subcharts programmatically so that I can expose a top-level set of values and computer subchart values
• I want to use Lua to alter subchart values so that I can read the values of one subchart and rewrite the values in another subchart (e.g. configuring a proxy based on the settings for a database or web server)
• I want to be able to intercept values in a top-level chart before and after a subchart's event handler executes so that I can pre-seed data, let the subchart calculate results, and then retrieve and use those results. (e.g. SSL certificate generation)

Templates

• I want to define template functions in Lua so that I can easily write custom template functions
• I want to render templates using a different template engine so that I can use my preferred template engine
  • Option A: Template engine implemented in pure Lua
  • Option B: Template engine invoked via exec call
• I want to intercept a template before it is rendered and be able to alter it so that I can dynamically replace parts of a template (example: regexp replace one template function/include with another)
• I want to replace a template in a subchart before it is rendred so that I can rewrite part of a chart dynamically

Rendered Manifests

• I want to modify a generated manifest so that I can insert additional information (e.g. Istio sidecar)
• I want to delete a generated manifest prior to it being loaded so that I can prevent an object from being created (e.g. subchart creates a manifest I don't want)
• I want to add a new manifest post-render so that I can create an object based on the results of a render process (e.g. RBAC generation, service generation, storage class generation)

Feature Discovery

• I want to query Kubernetes to see if a CRD exists so that I can decide whether to include a CRD definition
• I want to query whether a cluster supports RBAC so that I can decide whether to add RBAC rules
• I want to query for StorageClass so that I can pick an appropriate one for my PVC
• I want to look up DNS address (e.g. service discovery) so that I can find an endpoint, IP, or URL before installing/upgrading

Events

• I want to declare a function that responds to an event (e.g. "render") so that I can modify a chart/values at a particular point in the lifecycle
• I want to allow subcharts to run their event handlers by default so that I don't have to read all of the subcharts to know what they do
• I want to be able to turn off a subchart's lifecycle event by name so that I can disable a particular event handler
• I want to turn off all event handlers for a chart so that I can prevent it from intercepting any events
• I want to have an opportunity to initialize my chart's code every time it is loaded so that my chart can be initialized into a known state consistently
• I want to be able to perform installation-specific actions before an install so that I can do custom install logic
• I want to be able to perform post-installation actions so that I can set up an application (or notify the user about an installation) after the app has been submitted to Kubernetes
• I want to be able to do upgrade-specific logic before the upgrade has been submitted to Kubernetes
• I want to be able to do post-upgrade logic so that I can set up an app or notify a user
• I want to do custom logic before an app is deleted so that I can prepare for a deletion
• I want to do custom logic after a deletion so that I can ensure that a teardown is successful (e.g. if no other apps are using a namespace, delete teh namespace; if no other apps are using a CRD, delete the CRD definition...)
• I want to be able to declare custom logic that determines whether an installed or upgrade application is considered ready.
• I want to be able to perform specific logic when an application is considered ready.

Lua Libraries and Access

• I want to be able to break my Lua script into multiple files so that I can organize my code
• I want to be able to import code from subcharts so that I can re-use existing code
• I want to import existing pure Lua libraries that are stored in charts
• I want to use standard Lua libraries that do not have access to network or filesystem
• I want to optionally use network and filesystem libraries if approved by the user so that I can perform IO within a chart

Library Charts

• I want to use charts as template definition libraries so that I can re-use common template code
• I want to use charts as containers for Lua libraries so that I can re-use Lua code

Additional Considerations

• There are charts like OpenStack that have dozens of subcharts (and sub-subcharts)