Day 8/40
Kubernetes Deployment, Replication Controller and ReplicaSet Explained
Video Link
@piyushsachdeva
Git Repository
My Git Repo
We're going to learn about deployment and replicaset.
Assume there's a pod containing a nginx container running and because of an issue, the pod is stopped and crashed.
Actually in the real world, we don't tolerate stopping services, because we have some important customer and we are committed to our SLA with them and need to back to up and running state.
So, to overcome that type of problem we implement HA with having at least a copy of our app beside.
Let's say we are going to use replication controller that's manage by controller manager.
Note there's difference between replication controller and replicaset.
ReplicationController It creates a certain number of identical pods, and if a pod fails, replaces it. It also lets you update several pods or delete pods with one command. It's responsible for load balancing the traffic between replicas. replicas can be deploy on different nodes.
(Photo from the video)
1. Create a ReplicationController
---
apiVersion: v1
kind: ReplicationController
metadata:
name: nginx-rc
labels:
env: demo
spec:
template:
metadata:
name: nginx-pod
labels:
env: demo-pod
type: frontend
spec:
containers:
- name: nginx-container
image: nginx
ports:
- containerPort: 80
replicas: 3
root@localhost:~# kubectl apply -f day08-rc.yaml
replicationcontroller/nginx-rc created
root@localhost:~# kubectl get rc
NAME DESIRED CURRENT READY AGE
nginx-rc 3 3 3 9s
root@localhost:~# kubectl get pod
NAME READY STATUS RESTARTS AGE
nginx-rc-5x9bx 1/1 Running 0 17s
nginx-rc-ljwqs 1/1 Running 0 17s
nginx-rc-rsvfg 1/1 Running 0 17s
root@localhost:~# kubectl get pod -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-rc-5x9bx 1/1 Running 0 3m2s 10.244.1.3 lucky-luke-worker <none> <none>
nginx-rc-ljwqs 1/1 Running 0 3m2s 10.244.2.4 lucky-luke-worker2 <none> <none>
nginx-rc-rsvfg 1/1 Running 0 3m2s 10.244.2.5 lucky-luke-worker2 <none> <none>
ReplicaSet is the new version of ReplicationController and is declared in the same way, except it has more options for selectors.
---
apiVersion: apps/v1
kind: ReplicaSet
metadata:
name: nginx-rs
labels:
env: demo
spec:
template:
metadata:
name: nginx-pod
labels:
env: demo-pod
type: frontend
spec:
containers:
- name: nginx-container
image: nginx
ports:
- containerPort: 80
replicas: 3
selector:
matchLabels:
env: demo-pod
root@localhost:~# kubectl apply -f day08-rs.yaml
replicaset.apps/nginx-rs created
root@localhost:~# kubectl get rs
NAME DESIRED CURRENT READY AGE
nginx-rs 3 3 3 8s
root@localhost:~# kubectl get pod
NAME READY STATUS RESTARTS AGE
nginx-rc-5x9bx 1/1 Running 0 14m
nginx-rc-ljwqs 1/1 Running 0 14m
nginx-rc-rsvfg 1/1 Running 0 14m
nginx-rs-fw8xc 1/1 Running 0 13s
nginx-rs-mn2wp 1/1 Running 0 13s
nginx-rs-wvt7n 1/1 Running 0 13s
root@localhost:~# kubectl get pod -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-rc-5x9bx 1/1 Running 0 14m 10.244.1.3 lucky-luke-worker <none> <none>
nginx-rc-ljwqs 1/1 Running 0 14m 10.244.2.4 lucky-luke-worker2 <none> <none>
nginx-rc-rsvfg 1/1 Running 0 14m 10.244.2.5 lucky-luke-worker2 <none> <none>
nginx-rs-fw8xc 1/1 Running 0 19s 10.244.2.6 lucky-luke-worker2 <none> <none>
nginx-rs-mn2wp 1/1 Running 0 19s 10.244.1.5 lucky-luke-worker <none> <none>
nginx-rs-wvt7n 1/1 Running 0 19s 10.244.1.4 lucky-luke-worker <none> <none>
root@localhost:~# kubectl delete -f day08-rc.yaml
replicationcontroller "nginx-rc" deleted
root@localhost:~# kubectl get pod -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-rs-fw8xc 1/1 Running 0 3m19s 10.244.2.6 lucky-luke-worker2 <none> <none>
nginx-rs-mn2wp 1/1 Running 0 3m19s 10.244.1.5 lucky-luke-worker <none> <none>
nginx-rs-wvt7n 1/1 Running 0 3m19s 10.244.1.4 lucky-luke-worker <none> <none>
Live edit ReplicaSet and change the replicas to 5.
root@localhost:~# kubectl edit rs nginx-rs
replicaset.apps/nginx-rs edited
root@localhost:~# kubectl get rs
NAME DESIRED CURRENT READY AGE
nginx-rs 5 5 5 5m59s
root@localhost:~# kubectl get pod
NAME READY STATUS RESTARTS AGE
nginx-rs-5bxcm 1/1 Running 0 11s
nginx-rs-fw8xc 1/1 Running 0 6m6s
nginx-rs-jv4sd 1/1 Running 0 11s
nginx-rs-mn2wp 1/1 Running 0 6m6s
nginx-rs-wvt7n 1/1 Running 0 6m6s
root@localhost:~# kubectl get pod -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-rs-5bxcm 1/1 Running 0 18s 10.244.1.6 lucky-luke-worker <none> <none>
nginx-rs-fw8xc 1/1 Running 0 6m13s 10.244.2.6 lucky-luke-worker2 <none> <none>
nginx-rs-jv4sd 1/1 Running 0 18s 10.244.2.7 lucky-luke-worker2 <none> <none>
nginx-rs-mn2wp 1/1 Running 0 6m13s 10.244.1.5 lucky-luke-worker <none> <none>
nginx-rs-wvt7n 1/1 Running 0 6m13s 10.244.1.4 lucky-luke-worker <none> <none>
We can use 2 other ways to increase/decrease the replicas. One by editing the manifest and then apply with kubectl command, and other is what you can see below:
root@localhost:~# kubectl scale --replicas=10 rs/nginx-rs
replicaset.apps/nginx-rs scaled
root@localhost:~# kubectl get rs
NAME DESIRED CURRENT READY AGE
nginx-rs 10 10 10 11m
root@localhost:~# kubectl get pod
NAME READY STATUS RESTARTS AGE
nginx-rs-5bxcm 1/1 Running 0 5m29s
nginx-rs-7n6vt 1/1 Running 0 6s
nginx-rs-9qk4m 1/1 Running 0 6s
nginx-rs-dwtcb 1/1 Running 0 6s
nginx-rs-fw8xc 1/1 Running 0 11m
nginx-rs-hbxb8 1/1 Running 0 6s
nginx-rs-jv4sd 1/1 Running 0 5m29s
nginx-rs-kh4gq 1/1 Running 0 6s
nginx-rs-mn2wp 1/1 Running 0 11m
nginx-rs-wvt7n 1/1 Running 0 11m
root@localhost:~# kubectl get pod -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-rs-5bxcm 1/1 Running 0 5m41s 10.244.1.6 lucky-luke-worker <none> <none>
nginx-rs-7n6vt 1/1 Running 0 18s 10.244.1.8 lucky-luke-worker <none> <none>
nginx-rs-9qk4m 1/1 Running 0 18s 10.244.2.9 lucky-luke-worker2 <none> <none>
nginx-rs-dwtcb 1/1 Running 0 18s 10.244.2.8 lucky-luke-worker2 <none> <none>
nginx-rs-fw8xc 1/1 Running 0 11m 10.244.2.6 lucky-luke-worker2 <none> <none>
nginx-rs-hbxb8 1/1 Running 0 18s 10.244.2.10 lucky-luke-worker2 <none> <none>
nginx-rs-jv4sd 1/1 Running 0 5m41s 10.244.2.7 lucky-luke-worker2 <none> <none>
nginx-rs-kh4gq 1/1 Running 0 18s 10.244.1.7 lucky-luke-worker <none> <none>
nginx-rs-mn2wp 1/1 Running 0 11m 10.244.1.5 lucky-luke-worker <none> <none>
nginx-rs-wvt7n 1/1 Running 0 11m 10.244.1.4 lucky-luke-worker <none> <none>
2. Deployment
It provides some additional functionalities to the ReplicaSet. As a user, we create the deployment and it creates the ReplicaSet and then the ReplicaSet creates pod.
So, they are part of the deployment
(Photo from the video)
In RollingUpdate we can update the version of our app in almost zero downtime, which is very important to us and our customers. Also we can do the RollBack the changes we made easily.
Let's do it
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-deploy
labels:
env: demo
spec:
template:
metadata:
name: nginx-pod
labels:
env: demo-pod
type: frontend
spec:
containers:
- name: nginx-container
image: nginx
ports:
- containerPort: 80
replicas: 3
selector:
matchLabels:
env: demo-pod
root@localhost:~# kubectl apply -f day08-deploy.yaml
deployment.apps/nginx-deploy created
root@localhost:~# kubectl get node,deploy,rs,pod
NAME STATUS ROLES AGE VERSION
node/lucky-luke-control-plane Ready control-plane 5h44m v1.30.0
node/lucky-luke-worker Ready <none> 5h43m v1.30.0
node/lucky-luke-worker2 Ready <none> 5h43m v1.30.0
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/nginx-deploy 0/3 3 0 3s
NAME DESIRED CURRENT READY AGE
replicaset.apps/nginx-deploy-6bfd44d944 3 3 0 3s
NAME READY STATUS RESTARTS AGE
pod/nginx-deploy-6bfd44d944-24lf8 0/1 ContainerCreating 0 3s
pod/nginx-deploy-6bfd44d944-5bfm4 0/1 ContainerCreating 0 3s
pod/nginx-deploy-6bfd44d944-hfgbq 0/1 ContainerCreating 0 3s
root@localhost:~#
root@localhost:~# kubectl get all
NAME READY STATUS RESTARTS AGE
pod/nginx-deploy-6bfd44d944-24lf8 1/1 Running 0 2m45s
pod/nginx-deploy-6bfd44d944-5bfm4 1/1 Running 0 2m45s
pod/nginx-deploy-6bfd44d944-hfgbq 1/1 Running 0 2m45s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 5h47m
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/nginx-deploy 3/3 3 3 2m45s
NAME DESIRED CURRENT READY AGE
replicaset.apps/nginx-deploy-6bfd44d944 3 3 3 2m45s
Changing the version of our app
root@localhost:~# kubectl set image deployment/nginx-deploy nginx-container=nginx:1.9.1
deployment.apps/nginx-deploy image updated
root@localhost:~# kubectl get all
NAME READY STATUS RESTARTS AGE
pod/nginx-deploy-6bfd44d944-24lf8 1/1 Running 0 6m37s
pod/nginx-deploy-6bfd44d944-5bfm4 1/1 Running 0 6m37s
pod/nginx-deploy-6bfd44d944-hfgbq 1/1 Running 0 6m37s
pod/nginx-deploy-c4b878cbf-s9skb 0/1 ContainerCreating 0 11s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 5h51m
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/nginx-deploy 3/3 1 3 6m37s
NAME DESIRED CURRENT READY AGE
replicaset.apps/nginx-deploy-6bfd44d944 3 3 3 6m37s
replicaset.apps/nginx-deploy-c4b878cbf 1 1 0 12s
root@localhost:~# kubectl get all
NAME READY STATUS RESTARTS AGE
pod/nginx-deploy-6bfd44d944-5bfm4 1/1 Running 0 6m49s
pod/nginx-deploy-6bfd44d944-hfgbq 0/1 Terminating 0 6m49s
pod/nginx-deploy-c4b878cbf-2b7l2 1/1 Running 0 11s
pod/nginx-deploy-c4b878cbf-qkdql 0/1 ContainerCreating 0 1s
pod/nginx-deploy-c4b878cbf-s9skb 1/1 Running 0 23s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 5h51m
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/nginx-deploy 3/3 3 3 6m50s
NAME DESIRED CURRENT READY AGE
replicaset.apps/nginx-deploy-6bfd44d944 1 1 1 6m50s
replicaset.apps/nginx-deploy-c4b878cbf 3 3 2 25s
root@localhost:~# kubectl get all
NAME READY STATUS RESTARTS AGE
pod/nginx-deploy-c4b878cbf-2b7l2 1/1 Running 0 24s
pod/nginx-deploy-c4b878cbf-qkdql 1/1 Running 0 14s
pod/nginx-deploy-c4b878cbf-s9skb 1/1 Running 0 36s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 5h51m
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/nginx-deploy 3/3 3 3 7m2s
NAME DESIRED CURRENT READY AGE
replicaset.apps/nginx-deploy-6bfd44d944 0 0 0 7m2s
replicaset.apps/nginx-deploy-c4b878cbf 3 3 3 37s
Having the logs of our change
root@localhost:~# kubectl describe deploy nginx-deploy
Name: nginx-deploy
Namespace: default
CreationTimestamp: Thu, 27 Jun 2024 21:01:48 +0000
Labels: env=demo
Annotations: deployment.kubernetes.io/revision: 2
Selector: env=demo-pod
Replicas: 3 desired | 3 updated | 3 total | 3 available | 0 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: env=demo-pod
type=frontend
Containers:
nginx-container:
Image: nginx:1.9.1
Port: 80/TCP
Host Port: 0/TCP
Environment: <none>
Mounts: <none>
Volumes: <none>
Node-Selectors: <none>
Tolerations: <none>
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: nginx-deploy-6bfd44d944 (0/0 replicas created)
NewReplicaSet: nginx-deploy-c4b878cbf (3/3 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 8m43s deployment-controller Scaled up replica set nginx-deploy-6bfd44d944 to 3
Normal ScalingReplicaSet 2m17s deployment-controller Scaled up replica set nginx-deploy-c4b878cbf to 1
Normal ScalingReplicaSet 2m5s deployment-controller Scaled down replica set nginx-deploy-6bfd44d944 to 2 from 3
Normal ScalingReplicaSet 2m5s deployment-controller Scaled up replica set nginx-deploy-c4b878cbf to 2 from 1
Normal ScalingReplicaSet 115s deployment-controller Scaled down replica set nginx-deploy-6bfd44d944 to 1 from 2
Normal ScalingReplicaSet 115s deployment-controller Scaled up replica set nginx-deploy-c4b878cbf to 3 from 2
Normal ScalingReplicaSet 111s deployment-controller Scaled down replica set nginx-deploy-6bfd44d944 to 0 from 1
There are two revisions in the history of rollout of our deployment:
root@localhost:~# kubectl rollout history deploy/nginx-deploy
deployment.apps/nginx-deploy
REVISION CHANGE-CAUSE
1 <none>
2 <none>
We can rollback the changes:
root@localhost:~# kubectl rollout undo deploy/nginx-deploy
deployment.apps/nginx-deploy rolled back
root@localhost:~# kubectl rollout history deploy/nginx-deploy
deployment.apps/nginx-deploy
REVISION CHANGE-CAUSE
2 <none>
3 <none>
root@localhost:~# kubectl get all
NAME READY STATUS RESTARTS AGE
pod/nginx-deploy-6bfd44d944-82pwb 1/1 Running 0 2s
pod/nginx-deploy-6bfd44d944-pfgrk 1/1 Running 0 5s
pod/nginx-deploy-6bfd44d944-xbpzt 1/1 Running 0 8s
pod/nginx-deploy-c4b878cbf-2b7l2 1/1 Terminating 0 5m58s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 5h57m
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/nginx-deploy 3/3 3 3 12m
NAME DESIRED CURRENT READY AGE
replicaset.apps/nginx-deploy-6bfd44d944 3 3 3 12m
replicaset.apps/nginx-deploy-c4b878cbf 0 0 0 6m11s
root@localhost:~# kubectl get all
NAME READY STATUS RESTARTS AGE
pod/nginx-deploy-6bfd44d944-82pwb 1/1 Running 0 14s
pod/nginx-deploy-6bfd44d944-pfgrk 1/1 Running 0 17s
pod/nginx-deploy-6bfd44d944-xbpzt 1/1 Running 0 20s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 5h57m
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/nginx-deploy 3/3 3 3 12m
NAME DESIRED CURRENT READY AGE
replicaset.apps/nginx-deploy-6bfd44d944 3 3 3 12m
replicaset.apps/nginx-deploy-c4b878cbf 0 0 0 6m23s
root@localhost:~# kubectl describe deploy nginx-deploy
Name: nginx-deploy
Namespace: default
CreationTimestamp: Thu, 27 Jun 2024 21:01:48 +0000
Labels: env=demo
Annotations: deployment.kubernetes.io/revision: 3
Selector: env=demo-pod
Replicas: 3 desired | 3 updated | 3 total | 3 available | 0 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: env=demo-pod
type=frontend
Containers:
nginx-container:
Image: nginx
Port: 80/TCP
Host Port: 0/TCP
Environment: <none>
Mounts: <none>
Volumes: <none>
Node-Selectors: <none>
Tolerations: <none>
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: nginx-deploy-c4b878cbf (0/0 replicas created)
NewReplicaSet: nginx-deploy-6bfd44d944 (3/3 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 13m deployment-controller Scaled up replica set nginx-deploy-6bfd44d944 to 3
Normal ScalingReplicaSet 7m26s deployment-controller Scaled up replica set nginx-deploy-c4b878cbf to 1
Normal ScalingReplicaSet 7m14s deployment-controller Scaled down replica set nginx-deploy-6bfd44d944 to 2 from 3
Normal ScalingReplicaSet 7m14s deployment-controller Scaled up replica set nginx-deploy-c4b878cbf to 2 from 1
Normal ScalingReplicaSet 7m4s deployment-controller Scaled down replica set nginx-deploy-6bfd44d944 to 1 from 2
Normal ScalingReplicaSet 7m4s deployment-controller Scaled up replica set nginx-deploy-c4b878cbf to 3 from 2
Normal ScalingReplicaSet 7m deployment-controller Scaled down replica set nginx-deploy-6bfd44d944 to 0 from 1
Normal ScalingReplicaSet 84s deployment-controller Scaled up replica set nginx-deploy-6bfd44d944 to 1 from 0
Normal ScalingReplicaSet 81s deployment-controller Scaled down replica set nginx-deploy-c4b878cbf to 2 from 3
Normal ScalingReplicaSet 76s (x4 over 81s) deployment-controller (combined from similar events): Scaled down replica set nginx-deploy-c4b878cbf to 0 from 1
root@localhost:~# kubectl create deploy deploy/nginx-new --image=nginx --dry-run=client -o yaml
apiVersion: apps/v1
kind: Deployment
metadata:
creationTimestamp: null
labels:
app: deploy/nginx-new
name: deploy/nginx-new
spec:
replicas: 1
selector:
matchLabels:
app: deploy/nginx-new
strategy: {}
template:
metadata:
creationTimestamp: null
labels:
app: deploy/nginx-new
spec:
containers:
- image: nginx
name: nginx
resources: {}
status: {}
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