What is Helm and why is it needed? What does it define?

Helm is a package manager for Kubernetes that simplifies the installation, upgrade, and management of applications within a cluster.

Helm uses the concept of a "chart" — a collection of files that describe the Kubernetes resources needed to run an application. A chart defines:

• Kubernetes manifests (Deployment, Service, ConfigMap, etc.)
• Configuration values (values.yaml), which can be changed during installation
• Templates, which allow parameterizing manifests

An example of using Helm allows for quick deployment of complex applications with the desired settings, avoiding manual creation of numerous YAML files.

An example of a simple Deployment template in Helm:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ .Values.appName }}
spec:
  replicas: {{ .Values.replicas }}
  selector:
    matchLabels:
      app: {{ .Values.appName }}
  template:
    metadata:
      labels:
        app: {{ .Values.appName }}
    spec:
      containers:
      - name: {{ .Values.appName }}
        image: {{ .Values.image }}

Values for the template are set in the values.yaml file, which allows flexible deployment configuration.