Kubernetes Rolling Updates
Kubernetes Rolling Update
Application Life Cycle Management
I ran into some issue with my cluster and had to rebuild from scratch. Here is how my new cluster looks like:
pradeep@learnk8s$ kubectl get nodes -o wide
NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME
k8s Ready control-plane,master 4m42s v1.23.1 192.168.177.29 <none> Buildroot 2021.02.4 4.19.202 docker://20.10.12
k8s-m02 Ready <none> 4m21s v1.23.1 192.168.177.30 <none> Buildroot 2021.02.4 4.19.202 docker://20.10.12
pradeep@learnk8s$ kubectl get pods -A
NAMESPACE NAME READY STATUS RESTARTS AGE
kube-system coredns-64897985d-l9zmg 1/1 Running 0 4m34s
kube-system etcd-k8s 1/1 Running 1 4m45s
kube-system kindnet-4d4xb 1/1 Running 0 50s
kube-system kindnet-z27gn 1/1 Running 0 4m30s
kube-system kube-apiserver-k8s 1/1 Running 1 4m45s
kube-system kube-controller-manager-k8s 1/1 Running 1 4m45s
kube-system kube-proxy-n75w8 1/1 Running 0 4m34s
kube-system kube-proxy-v2mq5 1/1 Running 0 4m30s
kube-system kube-scheduler-k8s 1/1 Running 1 4m45s
kube-system storage-provisioner 1/1 Running 0 4m43s
Let us now create a deployment called kodekloud with image webapp-color and four replicas.
Here is the Docker image that we are going to use: https://hub.docker.com/r/kodekloud/webapp-color/tags?page=1&ordering=-last_updated. It has many versions of the same image (like v1, v2, and v3).
pradeep@learnk8s$ kubectl create deployment kodekloud --image=kodekloud/webapp-color --replicas=4
deployment.apps/kodekloud created
pradeep@learnk8s$ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
kodekloud-589c9f4b47-6fbqg 1/1 Running 0 47s 10.244.1.8 k8s-m02 <none> <none>
kodekloud-589c9f4b47-c75mz 1/1 Running 0 47s 10.244.1.7 k8s-m02 <none> <none>
kodekloud-589c9f4b47-s54tz 1/1 Running 0 47s 10.244.0.7 k8s <none> <none>
kodekloud-589c9f4b47-z2sqs 1/1 Running 0 47s 10.244.0.6 k8s <none> <none>
pradeep@learnk8s$ kubectl get deployment
NAME READY UP-TO-DATE AVAILABLE AGE
kodekloud 4/4 4 4 53s
Verify the current Image being used by the deployment
pradeep@learnk8s$ kubectl describe deployment kodekloud | grep Image
Image: kodekloud/webapp-color
pradeep@learnk8s$ minikube ssh -p k8s
_ _
_ _ ( ) ( )
___ ___ (_) ___ (_)| |/') _ _ | |_ __
/' _ ` _ `\| |/' _ `\| || , < ( ) ( )| '_`\ /'__`\
| ( ) ( ) || || ( ) || || |\`\ | (_) || |_) )( ___/
(_) (_) (_)(_)(_) (_)(_)(_) (_)`\___/'(_,__/'`\____)
$ curl 10.244.1.8:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #16a085;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-589c9f4b47-6fbqg!</h1>
</div>$ curl 10.244.1.7:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #16a085;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-589c9f4b47-c75mz!</h1>
</div>$ curl 10.244.0.7:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #2980b9;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-589c9f4b47-s54tz!</h1>
</div>$ curl 10.244.0.6:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #be2edd;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-589c9f4b47-z2sqs!</h1>
</div>$
Rolling Update
Also, find out the strategy used by this deployment
pradeep@learnk8s$ kubectl describe deployment kodekloud | grep Strategy
StrategyType: RollingUpdate
RollingUpdateStrategy: 25% max unavailable, 25% max surge
With RollingUpdate strategy, Pods are upgraded few at a time.
Now update the deployment to use a different version of the application kodekloud/webapp-color:v2.
For this, we need not delete or re-create the existing deployment. We can edit the deployment and modify the image name. Save with Esc + wq.
pradeep@learnk8s$ kubectl edit deployments kodekloud
# Please edit the object below. Lines beginning with a '#' will be ignored,
# and an empty file will abort the edit. If an error occurs while saving this file will be
# reopened with the relevant failures.
#
apiVersion: apps/v1
kind: Deployment
metadata:
annotations:
deployment.kubernetes.io/revision: "1"
creationTimestamp: "2022-02-15T07:13:38Z"
generation: 1
labels:
app: kodekloud
name: kodekloud
namespace: default
resourceVersion: "1592"
uid: e5728c54-8768-4d5c-b1b0-c3e33cf62062
spec:
progressDeadlineSeconds: 600
replicas: 4
revisionHistoryLimit: 10
selector:
matchLabels:
app: kodekloud
strategy:
rollingUpdate:
maxSurge: 25%
maxUnavailable: 25%
type: RollingUpdate
template:
metadata:
creationTimestamp: null
labels:
app: kodekloud
spec:
containers:
- image: kodekloud/webapp-color:v2
imagePullPolicy: Always
name: webapp-color
resources: {}
terminationMessagePath: /dev/termination-log
terminationMessagePolicy: File
dnsPolicy: ClusterFirst
restartPolicy: Always
schedulerName: default-scheduler
-- INSERT --
pradeep@learnk8s$ kubectl edit deployments kodekloud
deployment.apps/kodekloud edited
The pods should be recreated with new image. Looking at the AGE column, we can conclude that all four pods got re-created few seconds ago. If you notice carefully, the replicates is having a different Identifier now (changed from 589c9f4b47 to 8477b7849).
pradeep@learnk8s$ kubectl get pods
NAME READY STATUS RESTARTS AGE
kodekloud-8477b7849-4lgg2 1/1 Running 0 66s
kodekloud-8477b7849-b7grh 1/1 Running 0 44s
kodekloud-8477b7849-ndf4w 1/1 Running 0 66s
kodekloud-8477b7849-ww5qn 1/1 Running 0 47s
pradeep@learnk8s$ kubectl get deployments.apps
NAME READY UP-TO-DATE AVAILABLE AGE
kodekloud 4/4 4 4 16m
If we look at the Events section of this deployment, we can clearly see that the deployment-controller has Scaled Up the new replica set kodekloud-8477b7849 gradually from 1 to 4 and at the same time, old replica set kodekloud-589c9f4b47 got Scaled down from 4 to 0. This is becuase of the RollingUpdateStrategy: 25% max unavailable, 25% max surge.
For this current strategy, only one Pod can be down during the upgrade process (25%, meaning 1 out of total 4 pods in the deployment).
pradeep@learnk8s$ kubectl describe deployments.apps kodekloud
Name: kodekloud
Namespace: default
CreationTimestamp: Tue, 15 Feb 2022 12:43:38 +0530
Labels: app=kodekloud
Annotations: deployment.kubernetes.io/revision: 2
Selector: app=kodekloud
Replicas: 4 desired | 4 updated | 4 total | 4 available | 0 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: app=kodekloud
Containers:
webapp-color:
Image: kodekloud/webapp-color:v2
Port: <none>
Host Port: <none>
Environment: <none>
Mounts: <none>
Volumes: <none>
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: <none>
NewReplicaSet: kodekloud-8477b7849 (4/4 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 23m deployment-controller Scaled up replica set kodekloud-589c9f4b47 to 4
Normal ScalingReplicaSet 8m22s deployment-controller Scaled up replica set kodekloud-8477b7849 to 1
Normal ScalingReplicaSet 8m22s deployment-controller Scaled down replica set kodekloud-589c9f4b47 to 3
Normal ScalingReplicaSet 8m22s deployment-controller Scaled up replica set kodekloud-8477b7849 to 2
Normal ScalingReplicaSet 8m4s deployment-controller Scaled down replica set kodekloud-589c9f4b47 to 2
Normal ScalingReplicaSet 8m3s deployment-controller Scaled up replica set kodekloud-8477b7849 to 3
Normal ScalingReplicaSet 8m deployment-controller Scaled down replica set kodekloud-589c9f4b47 to 1
Normal ScalingReplicaSet 8m deployment-controller Scaled up replica set kodekloud-8477b7849 to 4
Normal ScalingReplicaSet 7m55s deployment-controller Scaled down replica set kodekloud-589c9f4b47 to 0
Verify the Image being used by the deployment now. It says, v2.
pradeep@learnk8s$kubectl describe deployment kodekloud| grep Image
Image: kodekloud/webapp-color:v2
Let’s collect the new IP address of the Pods and verify the application from the minikube node.
pradeep@learnk8s$ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
kodekloud-8477b7849-4lgg2 1/1 Running 0 4m2s 10.244.0.8 k8s <none> <none>
kodekloud-8477b7849-b7grh 1/1 Running 0 3m40s 10.244.0.9 k8s <none> <none>
kodekloud-8477b7849-ndf4w 1/1 Running 0 4m2s 10.244.1.9 k8s-m02 <none> <none>
kodekloud-8477b7849-ww5qn 1/1 Running 0 3m43s 10.244.1.10 k8s-m02 <none> <none>
As seen here, the application is now running the v2 version as indicated by the new headers:
<h2>
Application Version: v2
</h2>
pradeep@learnk8s$ minikube ssh -p k8s
_ _
_ _ ( ) ( )
___ ___ (_) ___ (_)| |/') _ _ | |_ __
/' _ ` _ `\| |/' _ `\| || , < ( ) ( )| '_`\ /'__`\
| ( ) ( ) || || ( ) || || |\`\ | (_) || |_) )( ___/
(_) (_) (_)(_)(_) (_)(_)(_) (_)`\___/'(_,__/'`\____)
$ curl 10.244.0.8:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #16a085;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-8477b7849-4lgg2!</h1>
<h2>
Application Version: v2
</h2>
</div>$ curl 10.244.0.9:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #16a085;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-8477b7849-b7grh!</h1>
<h2>
Application Version: v2
</h2>
</div>$ curl 10.244.1.9:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #16a085;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-8477b7849-ndf4w!</h1>
<h2>
Application Version: v2
</h2>
</div>$ curl 10.244.1.10:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #16a085;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-8477b7849-ww5qn!</h1>
<h2>
Application Version: v2
</h2>
</div>$
Another test is to verify the color of the web-app, it says green.
$ curl 10.244.0.8:8080/color
green$ curl 10.244.0.9:8080/color
green$ curl 10.244.1.9:8080/color
green$ curl 10.244.1.10:8080/color
green$
