Deployment Strategies

• When it comes to changing the version of the software (i.e. your application), a K8s deployment supports two strategies
• Recreate
• RollingUpdate

Recreate Strategy

• This strategy updates the replica set and terminates all of the Pods associated with deployment.
• The ReplicaSet noticias that it no longer has any replicase and re-creates all the Pods using new Image.
• Once the Pods are recreated, they are running the new version.
  
• While this strategy is simple and fast, it has one major drawback, it leads to certain downtime of your application.

RollingUpdate Strategy

• This strategy is generally preferable strategy for any user facing service.
• While it is slower than Recreate, the Rolling Update can rollout a new version of your service while it serving usertraffic, without having any downtime.
• Configure: There are two Parameters that can be used to tune the rolling update behavior
• maxUnavailable:
  • this parameter sets the maximum number of Pods that can be unavailable during a rolling update
  • It can be either set to an absolute (2) or percent (25%)
• maxSurge:
  • This parameter controls how many extra resources can be created to acheive a rollout.
  • It can be either set to an absolute (2) or percent (25%)
• Refer Here for the yaml spec with maxSurge and maxUnavailable
• Create a deployment
  
• Create a Service
  
• Lets create a new version and see how the deployment Refer Here
  

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DaemonSet

• I want to replicate Set of Pods where i want to have exactly one Pod on every Node in the cluster because this pod is my log agent
• A Daemonset ensures a copy of Pod is running across a set of nodes in the k8s cluster.
• As an example lets try to create a daemonset which runs an alpine container with sleep 1d
  
• Refer Here for the changes done

Jobs

• While long-running processes make up the large majority of workloads that are run in k8s cluster, there is often a need for short-lived one-off tasks.
• A K8S Job Object is made for handling these type of tasks
• A job creates a pod that run until succesful termination.
• A regular Pod will continually restart the container regardless of exit code.
• Jobs are useful for things you only want to do once, such as database migrations or batch jobs etc.
• Job Patterns
• One Shot
• Cron Jobs
• Lets create a Job which runs the alpine pod and we make it sleep for 60seconds so that the Job is completed. Refer Here for api reference
• Lets create a Job Spec Refer Here
  
• In Some Case we would like to run the job on certain time interval. Lets create a cron job Refer Here
  
• Next Steps:
• Configuration objects in k8s
• Health Checks
• Storage
• Services, Ingress
• AKS, EKS