Kubernetes

The outermost layer of Kubernetes(K8s) is K8s cluster, which is an abstraction that coordinates and manage all of our deployed application
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- The **k8s cluster** has 2 elements
    - **Control plane**: responsible for managing the cluster
    - **Nodes**: A Vm of an actual physical machine managed by K8s control plane
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The Control Plane coordinates all activities in your cluster, such as scheduling applications, maintaining applications' desired state, scaling applications, and rolling out new updates.
To deploy a containerized application to a k8s cluster
- Create a k8s deployment
- The Deployment instructs k8s how to create and update instances of your application. Once you've created a Deployment, the control plane schedules the application instances included in that Deployment to run on individual Nodes in the cluster.
- Once the application instances are created, a Kubernetes Deployment Controller continuously monitors those instances. If the Node hosting an instance goes down or is deleted, the Deployment controller replaces the instance with an instance on another Node in the cluster.
A Deployment will create Pod with the containerized application code inside it
- A Pod is an abstraction to host the application represent of >=1 application container
- We have to specify the Docker images that Deployment uses to create Pod
- A Pod may have multiple container
- Everything in a Pod shares storages, IP address, etc
- A Pod models an application specific "logical host"
- A Pod always live on a Node
- Deployment may create Pods in different Nodes depends on which is available
Service: To expose a Pod/ a set of Pods to the public so that it can receives traffic from the outside world
Scale
- Deployment only spin 1 pod by default
- Can config to increase the number of Replica
- We can use an integrated Load Balancer service to distribute the traffic evenly accross Pods

To create a Cronjob, just need to write a K8s yaml configuration with Kind: Cronjob