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What is a Deployment?

Learn that a Deployment manages Pods.

What is a Deployment?

A Deployment is the standard way to run stateless applications. You give the desired pod template and replica count; the Deployment creates a ReplicaSet, and the ReplicaSet creates the pods. When you change the image, the Deployment opens a new ReplicaSet and gradually replaces the old pods with new ones.

Deployment (web)
 └── ReplicaSet (web-7c5b9f6d8)
      ├── Pod web-7c5b9f6d8-abcde
      ├── Pod web-7c5b9f6d8-fghij
      └── Pod web-7c5b9f6d8-klmno

Seeing the hierarchy

To list the three levels together and see the ownership chain:

$ kubectl get deploy,rs,pods -l app=web
NAME                  READY   UP-TO-DATE   AVAILABLE
deployment.apps/web   3/3     3            3
NAME                             DESIRED   CURRENT   READY
replicaset.apps/web-7c5b9f6d8    3         3         3
$ kubectl get pod web-7c5b9f6d8-abcde -o jsonpath='{.metadata.ownerReferences[0].kind}'
ReplicaSet

Practice Create a deployment

Write two commands: create an api deployment with 2 replicas using the api:1.0 image; then list the deployments, ReplicaSets and pods labelled app=api in one command.

Starter code

terminal
# buraya yaz

Sample solution

terminal
kubectl create deployment api --image=api:1.0 --replicas=2
kubectl get deploy,rs,pods -l app=api

Expected output

deployment.apps/api created
NAME                  READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/api   2/2     2            2           12s
NAME                            DESIRED   CURRENT   READY   AGE
replicaset.apps/api-5d8f7c9b4   2         2         2       12s
NAME                      READY   STATUS    RESTARTS   AGE
pod/api-5d8f7c9b4-qrstu   1/1     Running   0          12s
pod/api-5d8f7c9b4-vwxyz   1/1     Running   0          12s

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 In the pod name web-7c5b9f6d8-abcde, what does 7c5b9f6d8 show?

  • The node name
  • The image version
  • A random number
  • The ReplicaSet ID derived from a hash of the pod template Correct answer

Explanation: When the template changes, a new hash means a new ReplicaSet.

2 List the deployments, ReplicaSets and pods together.

Question 
kubectl get deploy,____,pods -l app=web
Answer 
kubectl get deploy,rs,pods -l app=web

Explanation: rs is the abbreviation of replicasets.

3 Match.

Term Meaning
Deployment Manages versions and updates
ReplicaSet Keeps the replica count
Pod Runs the containers
ownerReferences Ownership chain

All lessons in Intermediate

1 What is Kubernetes?

  1. What is Kubernetes?
  2. Why Kubernetes?
  3. Cluster architecture
  4. Control plane
  5. Worker node
  6. Summary - What is Kubernetes

2 Minikube

  1. What is Minikube?
  2. Installing Minikube
  3. minikube start
  4. minikube status
  5. minikube dashboard
  6. Summary - Minikube

3 kubectl basics

  1. What is kubectl?
  2. kubectl get
  3. kubectl describe
  4. kubectl apply
  5. kubectl delete
  6. Summary - kubectl

4 Pod

  1. What is a Pod?
  2. Pod YAML
  3. Creating a Pod
  4. Pod status
  5. Multi-container Pod
  6. Summary - Pod

5 Deployment

  1. What is a Deployment?
  2. Deployment YAML
  3. Replica count
  4. Rolling update
  5. Rollback
  6. Summary - Deployment

6 ReplicaSet

  1. What is a ReplicaSet?
  2. ReplicaSet YAML
  3. ReplicaSet selector
  4. Scaling
  5. Self-healing
  6. Summary - ReplicaSet

7 Service

  1. What is a Service?
  2. ClusterIP
  3. NodePort
  4. LoadBalancer
  5. Service selector
  6. Summary - Service

8 ConfigMap

  1. What is a ConfigMap?
  2. ConfigMap YAML
  3. Environment variable
  4. Mounting as a volume
  5. kubectl create configmap
  6. Summary - ConfigMap

9 Secret

  1. What is a Secret?
  2. Secret types
  3. Secret YAML
  4. Mounting a Secret
  5. kubectl create secret
  6. Summary - Secret

10 Namespace

  1. What is a Namespace?
  2. kubectl get namespaces
  3. Creating a Namespace
  4. The -n flag
  5. Default Namespace
  6. Summary - Namespace

11 Labels and selectors

  1. What is a label?
  2. Adding labels
  3. Label selector
  4. kubectl get -l
  5. Equality and set selectors
  6. Summary - Labels

12 Project: Multi-tier app

  1. Project design
  2. Database Deployment
  3. Web Deployment
  4. ConfigMap and Secret
  5. Putting it together - multi-tier

13 Troubleshooting

  1. kubectl logs
  2. kubectl exec
  3. kubectl describe pod
  4. CrashLoopBackOff
  5. Pending Pod
  6. Summary - Troubleshooting

14 Intermediate final

  1. Challenge - Pod YAML
  2. Challenge - Deployment
  3. Challenge - Service
  4. Challenge - ConfigMap
  5. Challenge - Intermediate project