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Kubernetes Manifest Breakdown

A Kubernetes manifest file is a configuration file written in YAML or JSON that describes the desired state of objects in a Kubernetes cluster. The file defines a wide variety of attributes for managing different resources, such as Pods, Deployments, Services, and more.

Explanation​

1. apiVersion​

  • Specifies the Kubernetes API version used to create the object.
  apiVersion: apps/v1

2. kind​

  • Defines the type of resource being created. It could be a Pod, Deployment, Service, ReplicaSet, etc.
  kind: Deployment

3. metadata​

  • Provides information about the resource, such as name, namespace, labels, and annotations.
  metadata:
    name: my-deployment
    namespace: default
    labels:
      app: my-app
    annotations:
      description: "A deployment for my application"

4. spec​

  • Specifies the desired state of the object, including configuration details for the resource.
  spec:
    replicas: 3
    selector:
      matchLabels:
        app: my-app
    template:
      metadata:
        labels:
          app: my-app
      spec:
        containers:
        - name: my-container
          image: my-image:latest
          ports:
          - containerPort: 80

5. status​

  • Contains the current state of the object, such as whether it has been successfully created, running status, and more. This is automatically updated by the Kubernetes system and not typically defined in the manifest file
  status:
    replicas: 3
    availableReplicas: 3
    conditions:
    - type: Available
      status: "True"

6. replicas​

  • Specifies the number of identical Pods or replicas desired in the case of a Deployment or ReplicaSet
  replicas: 3

7. selector​

  • Used to identify the Pods that should be controlled by the Deployment or ReplicaSet. This helps Kubernetes decide which Pods match a certain Deployment or ReplicaSet based on their labels
  selector:
    matchLabels:
      app: my-app

8. template​

  • A template for the Pods that will be created. It includes the metadata and spec for the Pods, such as the containers to run and environment variables
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: my-container
        image: my-image:latest
        ports:
        - containerPort: 80

9. containers​

  • Defines the containers that should run within a Pod. Each container specification includes properties such as name, image, ports, and more
  containers:
    - name: my-container
      image: my-image:latest
      ports:
        - containerPort: 80

10. strategy​

  • Defines the strategy for deploying Pods in a Deployment, such as RollingUpdate or Recreate
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 1

11. resources​

  • Specifies the resource requirements and limits for a container
  resources:
    requests:
      memory: "64Mi"
      cpu: "250m"
    limits:
      memory: "128Mi"
      cpu: "500m"

12. affinity​

  • Controls where Pods are placed in a cluster based on rules.
  affinity:
    podAntiAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        - labelSelector:
            matchExpressions:
              - key: app
                operator: In
                values:
                  - my-app
          topologyKey: "kubernetes.io/hostname"

13. tolerations​

  • Allows Pods to be scheduled onto nodes with specific taints.
  tolerations:
    - key: "key"
      operator: "Equal"
      value: "value"
      effect: "NoSchedule"

14. livenessProbe​

  • Specifies how Kubernetes should check if the container is alive and healthy. livenessProbe: httpGet: path: /healthz port: 8080 initialDelaySeconds: 3 periodSeconds: 5 yaml

15. readinessProbe​

  • Specifies how Kubernetes checks if a container is ready to accept traffic.
  readinessProbe:
    httpGet:
      path: /readiness
      port: 8080
    initialDelaySeconds: 5
    periodSeconds: 5

16. nodeSelector​

  • Specifies which nodes the Pod can be scheduled on based on node labels.
  nodeSelector:
    disktype: ssd

17. resources​

  • Sets CPU and memory resource requests and limits for containers to define resource utilization.
  resources:
    requests:
      memory: "128Mi"
      cpu: "500m"
    limits:
      memory: "256Mi"
      cpu: "1"