Helm Chart for an etcd Cluster

Deploying applications on Kubernetes can often be a complex process. Helm charts simplify this by creating a package of pre-configured Kubernetes resources. In this post, we're going to create a Helm chart to deploy a production-ready etcd cluster.

What is a Helm Chart?

A Helm chart is a collection of files that describe a related set of Kubernetes resources. A single chart might be used to deploy something simple, like a memcached pod, or something complex, like a full web application stack with HTTP servers, databases, caches, and so on.

Prerequisites

• A Kubernetes Cluster ready
• kubectl
• Helm3

Installation

First, download Helm's installation script:

$ curl https://raw.githubusercontent.com/helm/helm/master/scripts/get-helm-3 > get_helm.sh

Next, give the script executable permissions:

$ chmod 700 get_helm.sh

Finally, run the installation script:

$ ./get_helm.sh

Setting Up the Helm Chart

Creating a Helm chart involves creating a specific directory structure with several different files. Here's a simple outline of our etcd Helm chart:

etcd/
├── Chart.yaml
├── templates/
│   ├── _helpers.tpl
│   ├── service.yaml
│   ├── statefulset.yaml
│   └── pvc.yaml
└── values.yaml

Understanding the Chart Files

Chart.yaml: This is where we define the chart's metadata.
Here's an example:

apiVersion: v3
name: etcd
version: 0.1.0
description: A Helm chart for deploying an etcd cluster in Kubernetes

templates/: This directory contains the template files that generate Kubernetes manifest files when the chart is installed.

_helpers.tpl: This is a place to put template helpers that you can reuse throughout your chart.

{{/* Generate the name */}}
{{- define "etcd.fullname" -}}
{{- .Chart.Name }}-{{ .Release.Name }}
{{- end -}}

service.yaml: This file defines a Service, which can be used to access your etcd cluster from other applications in your Kubernetes cluster.

apiVersion: v1
kind: Service
metadata:
  name: {{ include "etcd.fullname" . }}
spec:
  clusterIP: None
  ports:
    - port: 2379
      name: client
    - port: 2380
      name: peer
  selector:
    app: etcd

statefulset.yaml: This file defines a StatefulSet, which is used to manage the etcd Pods.

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: {{ include "etcd.fullname" . }}
spec:
  serviceName: "{{ include "etcd.fullname" . }}"
  replicas: {{ .Values.replicaCount }}
  selector:
    matchLabels:
      app: etcd
  template:
    metadata:
      labels:
        app: etcd
    spec:
      containers:
      - name: etcd
        image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
        ports:
        - containerPort: 2379
          name: client
        - containerPort: 2380
          name: peer
        volumeMounts:
        - name: data
          mountPath: /var/run/etcd
  volumeClaimTemplates:
  - metadata:
      name: data
    spec:
      accessModes: [ "ReadWriteOnce" ]
      storageClassName: {{ .Values.storageClass }}
      resources:
        requests:
          storage: {{ .Values.storageSize }}

pvc.yaml: Persistent Volume Claim (PVC) for storage of etcd data.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: data
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: {{ .Values.storageClass }}
  resources:
    requests:
      storage: {{ .Values.storageSize }}

values.yaml: This is where you define the default values for your chart. Here's a simple example:

replicaCount: 3
image:
  repository: quay.io/coreos/etcd
  tag: v3.5.0
storageClass: standard
storageSize: 1Gi

Run your etcd Helm chart

Make sure you are in the proper kubectl context and create a namespace named etcd.

$ kubectl create namespace etcd

Navigate to the directory containing the Chart files

$ helm install etcd-cluster . --namespace etcd

Output:

NAME: etcd-cluster
LAST DEPLOYED: Sat Aug  5 23:15:25 2023
NAMESPACE: etcd
STATUS: deployed
REVISION: 1
TEST SUITE: None

Get the resources

$ kubectl get all -n etcd 

Output:

NAME                      READY   STATUS    RESTARTS   AGE

pod/etcd-etcd-cluster-0   1/1     Running   0          104s

pod/etcd-etcd-cluster-1   1/1     Running   0          96s

pod/etcd-etcd-cluster-2   1/1     Running   0          91s

NAME                        TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)             AGE

service/etcd-etcd-cluster   ClusterIP   None         <none>        2379/TCP,2380/TCP   104s

NAME                                 READY   AGE

statefulset.apps/etcd-etcd-cluster   3/3     104s

Conclusion

This Helm chart sets up an etcd cluster on a Kubernetes environment, using best practices such as StatefulSets for pod identity and PVCs for data persistence.

This setup, however, is quite basic and might need to be adjusted based on your specific use case or production environment. Always remember to test your Helm charts thoroughly in a staging environment before deploying them in production.