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:

favoriteDrink: coffee

Now we can use this inside of a template:

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.

$ 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:

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:

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:

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:

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.