helm/docs/chart_template_guide/getting_started.md

# Getting Started with a Chart Template

In this section of the guide, we'll create a chart and then add a first template. The chart we created here will be used throughout the rest of the guide.

To get going, let's take a brief look at a Helm chart.

## Charts

As described in the [Charts Guide](../charts.md), Helm charts are structured like
this:

```
mychart/
  Chart.yaml
  values.yaml
  charts/
  templates/
  ...
```

The `templates/` directory is for template files. When Helm evaluates a chart,
it will send all of the files in the `templates/` directory through the
template rendering engine. It then collects the results of those templates
and sends them on to Kubernetes.

The `values.yaml` file is also important to templates. This file contains the
_default values_ for a chart. These values may be overridden by users during
`helm install` or `helm upgrade`.

The `Chart.yaml` file contains a description of the chart. You can access it
from within a template. The `charts/` directory _may_ contain other charts (which
we call _subcharts_). Later in this guide we will see how those work when it
comes to template rendering.

## A Starter Chart

For this guide, we'll create a simple chart called `mychart`, and then we'll
create some templates inside of the chart.

```console
$ helm create mychart
Creating mychart
```

From here on, we'll be working in the `mychart` directory.

### A Quick Glimpse of `mychart/templates/`

If you take a look at the `mychart/templates/` directory, you'll notice a few files
already there.

- `NOTES.txt`: The "help text" for your chart. This will be displayed to your users
  when they run `helm install`.
- `deployment.yaml`: A basic manifest for creating a Kubernetes [deployment](http://kubernetes.io/docs/user-guide/deployments/)
- `service.yaml`: A basic manifest for creating a [service endpoint](http://kubernetes.io/docs/user-guide/services/) for your deployment
- `_helpers.tpl`: A place to put template helpers that you can re-use throughout the chart

And what we're going to do is... _remove them all!_ That way we can work through our tutorial from scratch. We'll actually create our own `NOTES.txt` and `_helpers.tpl` as we go.

```console
$ rm -rf mychart/templates/*.*
```

When you're writing production grade charts, having basic versions of these charts can be really useful. So in your day-to-day chart authoring, you probably won't want to remove them.

## A First Template

The first template we are going to create will be a `ConfigMap`. In Kubernetes,
a ConfigMap is simply a container for storing configuration data. Other things,
like pods, can access the data in a ConfigMap.

Because ConfigMaps are basic resources, they make a great starting point for us.

Let's begin by creating a file called `mychart/templates/configmap.yaml`:

```yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: mychart-configmap
data:
  myvalue: "Hello World"
```

**TIP:** Template names do not follow a rigid naming pattern. However, we recommend
using the suffix `.yaml` for YAML files and `.tpl` for helpers.

The YAML file above is a bare-bones ConfigMap, having the minimal necessary fields.
In virtue of the fact that this file is in the `templates/` directory, it will
be sent through the template engine.

It is just fine to put a plain YAML file like this in the `templates/` directory.
When Helm reads this template, it will simply send it to Kubernetes as-is.

With this simple template, we now have an installable chart. And we can install
it like this:

```console
$ helm install ./mychart
NAME: full-coral
LAST DEPLOYED: Tue Nov  1 17:36:01 2016
NAMESPACE: default
STATUS: DEPLOYED

RESOURCES:
==> v1/ConfigMap
NAME                DATA      AGE
mychart-configmap   1         1m
```

In the output above, we can see that our ConfigMap was created. Using Helm, we
can retrieve the release and see the actual template that was loaded.

```console
$ helm get manifest full-coral

---
# Source: mychart/templates/configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: mychart-configmap
data:
  myvalue: "Hello World"
```

The `helm get manifest` command takes a release name (`full-coral`) and prints
out all of the Kubernetes resources that were uploaded to the server. Each file
begins with `---` to indicate the start of a YAML document, and then is followed
by an automatically generated comment line that tells us what template file
generated this YAML document.

From there on, we can see that the YAML data is exactly what we put in our
`configmap.yaml` file.

Now we can uninstall our release: `helm uninstall full-coral`.

### Adding a Simple Template Call

Hard-coding the `name:` into a resource is usually considered to be bad practice.
Names should be unique to a release. So we might want to generate a name field
by inserting the release name.

**TIP:** The `name:` field is limited to 63 characters because of limitations to
the DNS system. For that reason, release names are limited to 53 characters.
Kubernetes 1.3 and earlier limited to only 24 characters (thus 14 character names).

Let's alter `configmap.yaml` accordingly.

```yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-configmap
data:
  myvalue: "Hello World"
```

The big change comes in the value of the `name:` field, which is now
`{{ .Release.Name }}-configmap`.

> A template directive is enclosed in `{{` and `}}` blocks.

The template directive `{{ .Release.Name }}` injects the release name into the template. The values that are passed into a template can be thought of as _namespaced objects_, where a dot (`.`) separates each namespaced element.

The leading dot before `Release` indicates that we start with the top-most namespace for this scope (we'll talk about scope in a bit). So we could read `.Release.Name` as "start at the top namespace, find the `Release` object, then look inside of it for an object called `Name`".

The `Release` object is one of the built-in objects for Helm, and we'll cover it in more depth later. But for now, it is sufficient to say that this will display the release name that the library assigns to our release.

Now when we install our resource, we'll immediately see the result of using this template directive:

```console
$ helm install ./mychart
NAME: clunky-serval
LAST DEPLOYED: Tue Nov  1 17:45:37 2016
NAMESPACE: default
STATUS: DEPLOYED

RESOURCES:
==> v1/ConfigMap
NAME                      DATA      AGE
clunky-serval-configmap   1         1m
```

Note that in the `RESOURCES` section, the name we see there is `clunky-serval-configmap`
instead of `mychart-configmap`.

You can run `helm get manifest clunky-serval` to see the entire generated YAML.

At this point, we've seen templates at their most basic: YAML files that have template directives embedded in `{{` and `}}`. In the next part, we'll take a deeper look into templates. But before moving on, there's one quick trick that can make building templates faster: When you want to test the template rendering, but not actually install anything, you can use `helm install --debug --dry-run ./mychart`. This will render the templates. But instead of installing the chart, it will return the rendered template to you so you can see the output:

```console
$ helm install --debug --dry-run ./mychart
SERVER: "localhost:44134"
CHART PATH: /Users/mattbutcher/Code/Go/src/k8s.io/helm/_scratch/mychart
NAME:   goodly-guppy
TARGET NAMESPACE:   default
CHART:  mychart 0.1.0
MANIFEST:
---
# Source: mychart/templates/configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: goodly-guppy-configmap
data:
  myvalue: "Hello World"

```

Using `--dry-run` will make it easier to test your code, but it won't ensure that Kubernetes itself will accept the templates you generate. It's best not to assume that your chart will install just because `--dry-run` works.

In the next few sections, we'll take the basic chart we defined here and explore the Helm template language in detail. And we'll get started with built-in objects.