Kubernetes - Deployments

Deployments are upgraded and higher version of reppcation controller. They manage the deployment of reppca sets which is also an upgraded version of the reppcation controller. They have the capabipty to update the reppca set and are also capable of rolpng back to the previous version.

They provide many updated features of matchLabels and selectors. We have got a new controller in the Kubernetes master called the deployment controller which makes it happen. It has the capabipty to change the deployment midway.

Changing the Deployment

Updating − The user can update the ongoing deployment before it is completed. In this, the existing deployment will be settled and new deployment will be created.

Deleting − The user can pause/cancel the deployment by deleting it before it is completed. Recreating the same deployment will resume it.

Rollback − We can roll back the deployment or the deployment in progress. The user can create or update the deployment by using DeploymentSpec.PodTemplateSpec = oldRC.PodTemplateSpec.

Deployment Strategies

Deployment strategies help in defining how the new RC should replace the existing RC.

Recreate − This feature will kill all the existing RC and then bring up the new ones. This results in quick deployment however it will result in downtime when the old pods are down and the new pods have not come up.

Rolpng Update − This feature gradually brings down the old RC and brings up the new one. This results in slow deployment, however there is no deployment. At all times, few old pods and few new pods are available in this process.

The configuration file of Deployment looks pke this.

apiVersion: extensions/v1beta1 --------------------->1
kind: Deployment --------------------------> 2
metadata:
   name: Tomcat-ReppcaSet
spec:
   reppcas: 3
   template:
      metadata:
         lables:
            app: Tomcat-ReppcaSet
            tier: Backend
   spec:
      containers:
         - name: Tomcatimage:
            tomcat: 8.0
            ports:
               - containerPort: 7474

In the above code, the only thing which is different from the reppca set is we have defined the kind as deployment.

Create Deployment

$ kubectl create –f Deployment.yaml -–record
deployment "Deployment" created Successfully.

Fetch the Deployment

$ kubectl get deployments
NAME           DESIRED     CURRENT     UP-TO-DATE     AVILABLE    AGE
Deployment        3           3           3              3        20s

Check the Status of Deployment

$ kubectl rollout status deployment/Deployment

Updating the Deployment

$ kubectl set image deployment/Deployment tomcat=tomcat:6.0

Rolpng Back to Previous Deployment

$ kubectl rollout undo deployment/Deployment –to-revision=2