Docs
Getting Started
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, 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.
$ 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 runhelm install.deployment.yaml: A basic manifest for creating a Kubernetes deploymentservice.yaml: A basic manifest for creating a service endpoint 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.
$ 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:
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:
$ helm install full-coral ./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.
$ 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.
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:
$ helm install clunky-serval ./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:
$ helm install --debug --dry-run goodly-guppy ./mychart
install.go:149: [debug] Original chart version: ""
install.go:166: [debug] CHART PATH: /Users/ninja/mychart
NAME: goodly-guppy
LAST DEPLOYED: Thu Dec 26 17:24:13 2019
NAMESPACE: default
STATUS: pending-install
REVISION: 1
TEST SUITE: None
USER-SUPPLIED VALUES:
{}
COMPUTED VALUES:
affinity: {}
fullnameOverride: ""
image:
pullPolicy: IfNotPresent
repository: nginx
imagePullSecrets: []
ingress:
annotations: {}
enabled: false
hosts:
- host: chart-example.local
paths: []
tls: []
nameOverride: ""
nodeSelector: {}
podSecurityContext: {}
replicaCount: 1
resources: {}
securityContext: {}
service:
port: 80
type: ClusterIP
serviceAccount:
create: true
name: null
tolerations: []
HOOKS:
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 Chart Template Guide, we take the basic chart we defined here and explore the Helm template language in detail. And we’ll get started with built-in objects.
