What is a deployment?
The process of manually updating containerized applications can be time consuming and tedious. Upgrading a service to the next version requires starting the new version of the pod, stopping the old version of a pod, waiting and verifying that the new version has launched successfully, and sometimes rolling it all back to a previous version in the case of failure.
Performing these steps manually can lead to human errors, and scripting properly can require a significant amount of effort, both of which can turn the release process into a bottleneck.
A Kubernetes deployment makes this process automated and repeatable.
A deployment ensures the desired number of pods are running and available at all times. The update process is also wholly recorded, and versioned with options to pause, continue, and roll back to previous versions.
Deployment is higher in hierarchy: Above Pod, and above ReplicaSet
Can you list few features of deployment?
The Kubernetes deployment object lets you:
- Deploy a replica set or pod
- Update pods and replica sets
- Rollback to previous deployment versions
- Scale a deployment
- Pause or continue a deployment
How to create deployment?
Step 1: Create deployment definition yaml file:
apiVersion: apps/v1 kind: Deployment metadata: name: think-app-deployment labels: app: think-app env: eat spec: template: metadata: name: think-app-pod labels: app: think-app type: load-balancer spec: containers: - name: thinkscholar-nginx-container image: nginx replicas: 3 selector: matchLabels: type: load-balancer
Step2: Run the command:
kubectl create -f deployment-def.yaml
How to find all deployments?
$ kubectl get deployments NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE think-app-deployment 3 3 3 3 3s
Note: you can run get replicaset and get pods to check related replicaset and pods which were created along with other other replicaset and pods already present.
Output:
$ kubectl get rs NAME DESIRED CURRENT READY AGE think-app-deployment-985342 3 3 3 3s
$ kubectl get pods NAME READY STATUS RESTARTS AGE think-app-pod-53thy 1/1 Running 0 2s think-app-pod-k0xz6 1/1 Running 0 2s think-app-pod-q3vkg 1/1 Running 0 2s
Is there command to get all deployments, replicasets and pods present?
Yes. Run the command:
kubectl get all
Output:
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE deploy/think-app-deployment 3 3 3 3 3s NAME DESIRED CURRENT READY AGE rs/think-app-deployment-985342 3 3 3 3s NAME READY STATUS RESTARTS AGE po/think-app-pod-53thy 1/1 Running 0 2s po/think-app-pod-k0xz6 1/1 Running 0 2s po/think-app-pod-q3vkg 1/1 Running 0 2s
How to get detailed description about deployment?
Well to get detailed description of all deployments you can run:
kubectl describe deployment
Output:
Name: think-app-deployment
Namespace: default
CreationTimestamp: Tue, 15 Mar 2016 14:48:04 -0700
Labels: app=think-app
Selector: app=think-app
Replicas: 3 desired | 1 updated | 4 total | 3 available | 1 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: app=think-app
Containers:
nginx:
Image: nginx:1.161
Port: 80/TCP
Host Port: 0/TCP
Environment: <none>
Mounts: <none>
Volumes: <none>
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True ReplicaSetUpdated
OldReplicaSets: think-app-deployment-1564180365 (3/3 replicas created)
NewReplicaSet: think-app-deployment-3066724191 (1/1 replicas created)
Events:
FirstSeen LastSeen Count From SubObjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
1m 1m 1 {deployment-controller } Normal ScalingReplicaSet Scaled up replica set think-app-deployment-2035384211 to 3
22s 22s 1 {deployment-controller } Normal ScalingReplicaSet Scaled up replica set think-app-deployment-1564180365 to 1
22s 22s 1 {deployment-controller } Normal ScalingReplicaSet Scaled down replica set think-app-deployment-2035384211 to 2
22s 22s 1 {deployment-controller } Normal ScalingReplicaSet Scaled up replica set think-app-deployment-1564180365 to 2
21s 21s 1 {deployment-controller } Normal ScalingReplicaSet Scaled down replica set think-app-deployment-2035384211 to 1
21s 21s 1 {deployment-controller } Normal ScalingReplicaSet Scaled up replica set think-app-deployment-1564180365 to 3
13s 13s 1 {deployment-controller } Normal ScalingReplicaSet Scaled down replica set think-app-deployment-2035384211 to 0
13s 13s 1 {deployment-controller } Normal ScalingReplicaSet Scaled up replica set think-app-deployment-3066724191 to 1
To get detailed description about specific deployment, you should run:
kubectl describe deployment <deployment-name>
How to update deployment?
Well update the deployment details in the definition yaml:
- replicas
- image version
- labels
Apply the changes:
kubectl apply -f deployment-def.yaml
Can I update version of image in deployment without applying changes to definition yaml?
Yes.
kubectl set image deployment/thinkscholar-deployment nginx=ngixn:2.0.1
Note: Just be careful, that you didn’t update deployment definition file. Hence you should be careful using this definition file in future
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