Microtemplates with Helm

Context and problem

The ability to configure containers with external definitions is a key part of 12 factor apps. As organisations adopt containers these external definitions tend to travel as shell scripts included in the code repository. These shell scripts become unwieldy quickly and have to be rewritten when an organisation moves to an orchestration platform.

Solution

Adopt a template engine early in the modernization cycle can help mitigate the problem of shell scripts and prepare an organisation for the move towards kubernetes.

Issues and considerations

Helm as a dependancy may require additional training for the organisation.

When to use this scenario

Helm is useful from Replatform point of the journey onwards. This microtemplating option is targeting the developer loop and is especially useful at the start of the Replatform roadmap.

Example

  1. Prerequisits

  2. Create a file called `Chart.yaml file and add the following content

apiVersion: v2
name: top-helm-app
type: application
version: 0.1.0
appVersion: "1.16.0"
  1. Create folder called templates and create file called pod.yaml with the following content 
apiVersion: v1
kind: Pod
metadata:
  labels:
    app: top-helm-pod
  name: top-helm-top-pod
spec:
  restartPolicy: Never
  containers:
  - command:
    - top
    image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
    name: top-helm-container
    resources: {}
  1. Create a file called values.yaml with the following content
image:
  repository: docker.io/library/alpine
  tag: "3.15.4"

  1. Validate the pod template is generated correctly by running helm template .

    helm template .

---
# Source: top-helm-app/templates/pod.yaml
apiVersion: v1
kind: Pod
metadata:
name: top-helm-pod
spec:
containers:
    command:
    - top
    name: top-helm-container
    image: "docker.io/library/alpine:3.15.4"

Next steps

  1. Run the file with podman 

    helm template . | podman play kube -

  2. Delete the pod 

    podman pod stop top-helm-top-pod 
podman pod rm top-helm-top-pod

Standalone Podman