Exercise 1: Create a Pod Manifest to run alpine with sleep 1d

• Refer Here for the changes made
  
• Now lets look at describing out kubectl describe <resource-name> <object-name>
  

Using Port forwarding

• Lets launch the pod from activity1
  

Getting More Information With Logs

Activity 3: Create a Pod with container which has CMD to get container to exited state

• Refer Here for the changes
• As the container gets into the exited state pod tries to restart the container and this happens continuously
• To deal with these kind of continuous restarts we will be learning probes.

Activity 4: Start activity 1

• create a pod with spec activity1.yaml
• Now shutdown the node where activity1 is running. (Simulating some error on the node)
  
• Node is shutdown, Pod is not accesible, but k8s is not scheduling this pod to run on other node
  

Workload Resources

• Kubernetes Provides different workload resources
• Replicaset:
  • This is used to create multiple replications of your Pod which is running your application
• Deployment
• Statefulset
• DaemonSet
• Job and CronJob
• If we try to use the above workloads then the desired state is maintained
• Since Pod cannot maintain its own state i.e. if the Pod is Down, schedule the Pod on a new node
  
• Running our application in the Workload resources which maintain some kind of desired state is what we want.
• Before we understand workload resources, we need to understand the concept of labels and annotations in kubernetes

Labels

• Labels are key/value pairs that can be attached to k8s objects such as Pods, replicasets etc.
• They are arbitrary and are useful for identifying information about k8s objects
• They provide the foundation for grouping objects
• Labels have very simple syntax.
• Keys can be broken down into two parts an optional prefix and a name seperated by slahs (dots, underscores, dashes(hypens)) can be used in names
• Values are strings with maximum of 63 characters
• Examples:

| key | value |
| — | ——|
| qt.com/app-version | 1.0.0 |
| appVersion | 1.0.0 |
| app.version | 1.0.0 |
| project | qtidentitiy |
* Lets try to apply labels

* Now lets get labels

* Label Selectors: These are used to filter k8s objects based on set of labels


* Lets create labels in the declarative approach. Refer Here for the Pod manifest



* Selectors in the Yaml will be in the format of

selector:
  app: web
  env: prod

Annotations

• Annotations are also key value pairs like labels which provide a place to store additional metadata for k8s objects with the sole purpose of assisting tools and libraries

metadata:
  annotations:
    qt.com/icons-url: "https://qt.com/icon-main.png"

ReplicaSets

• If we want multiple replicas of the application in Pod running and maintaing the state of number of replicas we use replica sets
  

Activity 5: Lets create a replicaset to create 2 replicas of jenkins (Pod)

• Refer Here for api reference
• Refer Here for Replicaset Spec
• Refer Here for the ReplicaSet Manifest created
  
  
• Now delete one pod manually to see what replica set does