Kubernetes Deployment Update Strategy

Kubernetes creates a second ReplicaSet, where it deploys the new pods and removes the old one from the original ReplicaSet

2 Types of Update Strategies in Kubernetes.  

Recreate: Removes the previous version and loads the new, good for development(interrupting the service). 

RollingUpdate (default): it updates to a new version gradually based on configured parameters.

The parameters are: 

maxUnavailable: The number/percentage of pods that can be unavailable during the update. 

maxSurge: The number/percentage of pods that can exceed the replicas requested. 

minReadySeconds: The number(only) of seconds to wait before the next pod’s creation. 

Kubernetes ReplicaSet selector with matchExpressions

ReplicaSet is a tool to manage the pod replicas and update strategies, and it is more flexible than the replication controller. 

It provides set-based labels selection support instead of the equality-based labels (ReplicationController). 

With equality-based (a replication controller) labels support, you can match labels only with an "is equal" or "is not equal" assertion. 

Match a group of pods that has a label zone with the value prod or test, but not both of them

With a set-based labels selection, you can express more powerful assertions, like in, not in, or exists. 

Match all the pods with the prod label in prod and test, using the matchExpressions property of the selector 

deployment_replicaset.yaml

--- 
apiVersion: apps/v1
kind: Deployment
metadata: 
  name: myapp-deployment_replicatset
spec: 
   replicas: 3  
   selector:    
     matchLabels:
       app: myapp
     matchExpressions:
       - {key: zone, operator: In, values: [prod, test]} 
   template:    
     metadata:         
       labels:           
         app: myapp           
         zone: prod           
         version: v1        
     spec:           
       containers:             
         - name: myapp-frontendmvc              
           image: makader/myapp:frontendmvc-v1              
           ports:               
             - containerPort: 80

Deploy ASP.NET CORE application with the Kubernetes Deployments

Update the application with a rolling update strategy that releases new pods more gradually, one pod at a time. 

Roll back the application to a specific version of the deploy history using the deployment. 

Run the command without --restart=Never (Deploy ASP.NET Core Application images in Kubernetes (K8s) & POD). Command to create a simple deployment 

 kubectl run frontendmvcv1 --image=makader/myapp:frontendmvc-v1 --port 80 

kubectl get deployment frontendmvcv1