helm/docs/chart_template_guide/values_files.md

# Values Files

In the previous section we looked at the built-in objects that Helm templates offer. One of the four built-in objects is `Values`. This object provides access to values passed into the chart. Its contents come from four sources:

- The `values.yaml` file in the chart
- If this is a subchart, the `values.yaml` file of a parent chart
- A values file if passed into `helm install` or `helm update` with the `-f` flag (`helm install -f myvals.yaml ./mychart`)
- Individual parameters passed with `--set` (such as `helm install --set foo=bar ./mychart`)

The list above is in order of specificity: `values.yaml` is the default, which can be overridden by a parent chart's `values.yaml`, which can in turn be overridden by a user-supplied values file, which can in turn be overridden by `--set` parameters.

Values files are plain YAML files. Let's edit `mychart/values.yaml` and then edit our ConfigMap template.

Removing the defaults in `values.yaml`, we'll set just one parameter:

```yaml
favoriteDrink: coffee
```

Now we can use this inside of a template:

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

Notice on the last line we access `favoriteDrink` as an attribute of `Values`: `{{ .Values.favoriteDrink}}`.

Let's see how this renders.

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

Because `favoriteDrink` is set in the default `values.yaml` file to `coffee`, that's the value displayed in the template. We can easily override that by adding a `--set` flag in our call to `helm install`:

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

Since `--set` has a higher precedence than the default `values.yaml` file, our template generates `drink: slurm`.

Values files can contain more structured content, too. For example, we could create a `favorite` section in our `values.yaml` file, and then add several keys there:

```yaml
favorite:
  drink: coffee
  food: pizza
```

Now we would have to modify the template slightly:

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

While structuring data this way is possible, the recommendation is that you keep your values trees shallow, favoring flatness. When we look at assigning values to subcharts, we'll see how values are named using a tree structure.

## Deleting a default key

If you need to delete a key from the default values, you may override the value of the key to be `null`, in which case Helm will remove the key from the overridden values merge.

For example, the stable Drupal chart allows configuring the liveness probe, in case you configure a custom image. Here are the default values:
```yaml
livenessProbe:
  httpGet:
    path: /user/login
    port: http
  initialDelaySeconds: 120
```

If you try to override the livenessProbe handler to `exec` instead of `httpGet` using `--set livenessProbe.exec.command=[cat,docroot/CHANGELOG.txt]`, Helm will coalesce the default and overridden keys together, resulting in the following YAML:
```yaml
livenessProbe:
  httpGet:
    path: /user/login
    port: http
  exec:
    command:
    - cat
    - docroot/CHANGELOG.txt
  initialDelaySeconds: 120
```

However, Kubernetes would then fail because you can not declare more than one livenessProbe handler. To overcome this, you may instruct Helm to delete the `livenessProbe.httpGet` by setting it to null:
```sh
helm install stable/drupal --set image=my-registry/drupal:0.1.0 --set livenessProbe.exec.command=[cat,docroot/CHANGELOG.txt] --set livenessProbe.httpGet=null
```

At this point, we've seen several built-in objects, and used them to inject information into a template. Now we will take a look at another aspect of the template engine: functions and pipelines.