common/README.md

Common: The Helm Helper Chart

This chart was originally forked from incubator/common, which is designed to make it easier for you to build and maintain Helm charts.

It provides utilities that reflect best practices of Kubernetes chart development, making it faster for you to write charts.

Resource Kinds

Kubernetes defines a variety of resource kinds, from Secret to StatefulSet. We define some of the most common kinds in a way that lets you easily work with them.

The resource kind templates are designed to make it much faster for you to define basic versions of these resources. They allow you to extend and modify just what you need, without having to copy around lots of boilerplate.

To make use of these templates you must define a template that will extend the base template (though it can be empty). The name of this template is then passed to the base template, for example:

{{- template "common.service" (list . .Values.service "mychart.service") -}}
{{- define "mychart.service" -}}
## Define overrides for your Service resource here, e.g.
# metadata:
#   labels:
#     custom: label
# spec:
#   ports:
#     - port: 8080
#       targetPort: http
#       protocol: TCP
#       name: http
{{- end -}}

Note that the common.service template defines three parameters:

• The root context (usually .)
• A dictionary of values which are used in the template
• A optional template name containing the service definition overrides

A limitation of the Go template library is that a template can only take a single argument. The list function is used to workaround this by constructing a list or array of arguments that is passed to the template.

The common.service template is responsible for rendering the templates with the root context and merging any overrides. As you can see, this makes it very easy to create a basic Service resource without having to copy around the standard metadata and labels.

Each implemented base resource is described in greater detail below.

common.deployment

The common.deployment template accepts a list of three values:

• the top context
• $deployment, a dictionary of values used in the deployment template
• $autoscaling, a dictionary of values used in the hpa template
• [optional] the template name of the overrides

It defines a basic Deployment with the following settings:

Value	Description
$deployment.replicaCount	Number of replica. If autoscaling enabled, this field will be ignored
$deployment.imagePullSecrets	[optional] Name of Secret resource containing private registry credentials
$deployment.podSecurityContext	[optional] Security options for pod
$deployment.nodeSelector	[optional] Node labels for pod assignment
$deployment.affinity	[optional] Expressions for affinity
$deployment.tolerations	[optional] Toleration labels for pod assignment
$autoscaling.enabled	[optional] Set this to true to enable autoscaling

Underneath the hood, it uses common.container.

By default, the pod template within the deployment defines the labels

app.kubernetes.io/name: {{ template "common.name" }}
app.kubernetes.io/instance: {{ .Release.Name }}

as this is also used as the selector. The standard set of labels are not used as some of these can change during upgrades, which causes the replica sets and pods to not correctly match.

Example use:

{{- template "common.deployment" (list . .Values .Values.autoscaling) -}}

## The following is the same as above:
# {{- template "common.deployment" (list . .Values .Values.autoscaling "mychart.deployment") -}}
# {{- define "mychart.deployment" -}}
# {{- end -}}

common.service

The common.service template accepts a list of three values:

• the top context
• $service, a dictionary of values used in the service template
• [optional] the template name of the overrides

It creates a basic Service resource with the following defaults:

• Service type (ClusterIP, NodePort, LoadBalancer) made configurable by $service.type

• Named port http configured on port $service.port

• Selector set to

  app.kubernetes.io/name: {{ template "common.name" }}
  app.kubernetes.io/instance: {{ .Release.Name }}
  

  to match the default used in the Deployment resource

Example template:

{{- template "common.service" (list . .Values.service "mychart.mail.service") -}}
{{- define "mychart.mail.service" -}}
{{- $top := first . -}}
metadata:
  name: {{ template "common.fullname" $top }}-mail  # overrides the default name to add a suffix
  labels:                                           # appended to the labels section
    protocol: mail
spec:
  ports:                                            # composes the `ports` section of the service definition.
  - name: smtp
    port: 25
    targetPort: 25
  - name: imaps
    port: 993
    targetPort: 993
  selector:                                         # this is appended to the default selector
    protocol: mail
{{- end }}
---
{{ template "common.service" (list . .Values.service "mychart.web.service") -}}
{{- define "mychart.web.service" -}}
{{- $top := first . -}}
metadata:
  name: {{ template "common.fullname" $top }}-www   # overrides the default name to add a suffix
  labels:                                           # appended to the labels section
    protocol: www
spec:
  ports:                                            # composes the `ports` section of the service definition.
  - name: www
    port: 80
    targetPort: 8080
{{- end -}}

The above template defines two services: a web service and a mail service.

The most important part of a service definition is the ports object, which defines the ports that this service will listen on. Most of the time, selector is computed for you. But you can replace it or add to it.

The output of the example above is:

apiVersion: v1
kind: Service
metadata:
  labels:
    app.kubernetes.io/instance: release-name
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/name: mychart
    app.kubernetes.io/version: 1.16.0
    helm.sh/chart: mychart-0.1.0
    protocol: www
  name: release-name-mychart-www
spec:
  ports:
  - name: www
    port: 80
    targetPort: 8080
  selector:
    app.kubernetes.io/instance: release-name
    app.kubernetes.io/name: mychart
  type: ClusterIP
---
apiVersion: v1
kind: Service
metadata:
  labels:
    app.kubernetes.io/instance: release-name
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/name: mychart
    app.kubernetes.io/version: 1.16.0
    helm.sh/chart: mychart-0.1.0
    protocol: mail
  name: release-name-mychart-mail
spec:
  ports:
  - name: smtp
    port: 25
    targetPort: 25
  - name: imaps
    port: 993
    targetPort: 993
  selector:
    app.kubernetes.io/instance: release-name
    app.kubernetes.io/name: mychart
    protocol: mail
  type: ClusterIP