helm/docs/chart_best_practices/pods.md

Pods and PodTemplates

This part of the Best Practices Guide discusses formatting the Pod and PodTemplate portions in chart manifests.

The following (non-exhaustive) list of resources use PodTemplates:

• Deployment
• ReplicationController
• ReplicaSet
• DaemonSet
• StatefulSet

Images

A container image should use a fixed tag or the SHA of the image. It should not use the tags latest, head, canary, or other tags that are designed to be "floating".

Images may be defined in the values.yaml file to make it easy to swap out images.

image: {{ .Values.redisImage | quote }}

An image and a tag may be defined in values.yaml as two separate fields:

image: "{{ .Values.redisImage }}:{{ .Values.redisTag }}"

ImagePullPolicy

The imagePullPolicy should default to an empty value, but allow users to override it:

imagePullPolicy: {{ default "" .Values.imagePullPolicy | quote }}

PodTemplates Should Declare Selectors

All PodTemplate sections should specify a selector. For example:

selector:
  matchLabels:
      app: MyName
template:
  metadata:
    labels:
      app: MyName

This is a good practice because it makes the relationship between the set and the pod.

But this is even more important for sets like Deployment. Without this, the entire set of labels is used to select matching pods, and this will break if you use labels that change, like version or release date.