Kubernetes | Deployment

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Deployment

An API object that manages a replicated application, typically by running Pods with no local state.

📌 A Kubernetes Deployment is a higher-level object that provides capabilities such as seamless rolling updates to underlying instances, the ability to undo changes, and the option to pause and resume changes as required.
📌 Kubernetes Deployments are commonly used to deploy and manage multiple instances of applications in a production environment.

Key Reasons for Using a Deployment

  1. Rolling Updates:
    • This allows for seamless updates to the underlying instances (pods) without downtime by gradually replacing the old versions of pods with new ones.
    • Don't upgrade all at once, as it may impact users accessing your applications. Instead, upgrade one after the other, using a process called rolling updates.
  2. Rollback:
    • If something goes wrong during an update, a Deployment can undo changes and revert to a previous stable state.
    • Undo the recent change. Roll back the changes that were recently carried out.
  3. Pause and Resume:
    • Updates can be paused and resumed, which is useful for controlling the deployment process and debugging issues.
    • You don’t want to apply each change immediately after the command is run. Instead, you would like to apply a pause to your environment, make the changes, and then resume so that all the changes are rolled out together.

Deployment with YAML

Template:

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apiVersion: apps/v1
kind: Deployment
metadata:
  name: [custom_name]
  labels:
    [custom_key]: [custom_value]
    ...
spec:
  template:
    [[ POD ]]
  replicas: [number]
  selector:
    matchLabels:
      [pod_labels_key]: [pod_labels_value]

deployment-definition.yml

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apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deployment
  labels:
    app: myapp
    type: front-end
spec:
  template:
    metadata:
      name: myapp-pod
      labels:
        app: myapp
        type: front-end
    spec:
      containers:
        - name: nginx-container
          image: nginx
  replicas: 3
  selector:
    matchLabels:
      type: front-end

RUN commands

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$ kubectl create -f deployment-definition.yml
$ kubectl get deployments
$ kubectl get replicaset
$ kubectl get pods
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$ kubectl get all

👍 Quickly create Kubernetes YAML Templates
In k8s version 1.19+, we can specify the –replicas option to create a deployment with 3 replicas.

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$ kubectl create deployment --image=httpd:2.4-alpine httpd-frontend --replicas=3

kubectl create vs. kubectl run

📝 kubectl create

Create a resource from a file or from stdin.
JSON and YAML formats are accepted.

Create a deployment

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$ kubectl create deployment --image=nginx nginx

Generate Deployment YAML file (-o yaml). Don’t create it(–dry-run) and save it to a file.

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$ kubectl create deployment --image=nginx nginx --dry-run=client -o yaml > nginx-deployment.yaml

Make necessary changes to the file (for example, adding more replicas) and then create the deployment.

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$ kubectl create -f nginx-deployment.yaml

📝 kubectl run

Create and run a particular image in a pod.

Create an NGINX Pod

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$ kubectl run nginx --image=nginx

Generate POD Manifest YAML file (-o yaml). Don’t create it (–dry-run) and save it to a file.

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$ kubectl run redis --image=redis --dry-run=client -o yaml > redis_template.yaml
$ kubectl create -f redis_template.yaml

References