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# Common Library

!!! note

    The Common library chart is not meant to be installed directly, application
    charts use the Common library as a dependency.
    See the [app template](../app-template/index.md) for an example how to
    deploy it.

## Background

In Helm 3, their team introduced the concept of a
[Library chart](https://helm.sh/docs/topics/library_charts/).

> A library chart is a type of Helm chart that defines chart primitives or
> definitions which can be shared by Helm templates in other charts. This
> allows users to share snippets of code that can be re-used across charts,
> avoiding repetition and keeping charts DRY.

The common library was created because I saw many charts requiring only a
few select configuration options in their Helm charts.

!!! note

    Take one of the many applications like `sonarr` or `nzbget`. Each of these
    charts only require setting `service`, `port`, `persistence`, `ingress`
    and `image` since state and app configuration is handled by the application
    itself.

In order to stay somewhat DRY (Don't Repeat Yourself) and keeping with Helm 3
usage for a Library chart, I saw this pattern and decided it was worth it to
create a library. This means each one of these app charts has a
dependency on what I call the `common` library.

## Source code

The source code for the common library chart can be found
[here](https://github.com/bjw-s/helm-charts/tree/main/charts/library/common).