Kubernetes – Objects – simplifying concepts

Hi All,

GREETINGS FOR THE DAY 🙂 LIFE IS BEAUTIFUL 🙂

We are discussing Kubernetes. In previous few articles we discussed

• What is Kubernetes ? – https://knowledge-junction.in/2021/09/03/kubernetes-introduction-starting-point-for-beginners-helps-to-prepare-the-interview/
• Setting up local environment for Kubernetes – https://knowledge-junction.in/2021/09/11/kubernetes-simplifying-setting-up-local-environment-creating-kubernetes-cluster-locally-helps-in-interview-preparation-kubernetes-for-beginners/
• Yaml file guide / reference – https://knowledge-junction.in/2021/09/04/complete-guide-to-yaml/
• Kubernetes – Setting up kubernetes cluster for development on Windows 10 box using minikube – https://knowledge-junction.in/2022/05/06/kubernetes-setting-up-kubernetes-cluster-for-development-on-windows-10-box-using-minikube/
• Kubernetes – POD – https://knowledge-junction.in/2022/05/05/kubernetes-pod/

Today in this article we will discuss about – Kubernetes objects. We discussed about Kubernetes – POD which is one of the Kubernetes object

Take away from this article

• What are Kubernetes objects
• How to get list of Kubernetes objects
• How to create Kubernetes objects

What are Kubernetes objects

• Kubernetes objects which are the entities and integral part of Kubernetes cluster
• We can say that Kubernetes objects are building blocks of Kubernetes cluster
• Kubernetes objects are used to
  • To deploy our containerised applications (docker images)
  • On which node in Kubernetes cluster containerised applications are running
  • To maintain the healthy state of Kubernetes cluster
  • To make sure our containerised applications are working in healthy state

There are lots of Kubernetes object. We can get list of all kubernetes objects by executing the command

 kubectl api-resources

Output of the above CMDLET will be

Following are some/popular Kubernetes objects – Here I am adding just short description for each object and then we will have detailed article for each object like we have separate detailed article for POD

• Namespaces
  • Namespaces come into the picture when we want to share single cluster with multiple users / teams
  • Namespaces provides us scope for names
  • Kubernetes comes with three default namespaces:
    • default The default namespace for objects having no namespaces
    • kube-system The namespace for objects created by the Kubernetes system
    • kube-public This namespace is created automatically and is readable by all users (including those not authenticated)

• PODs
  • Kubernetes system dosent understand our containerised application, Kubernetes understand PODs, those are wrapper for our containerized application in Kubernetes
  • In nutshell, POD contains one more containers
  • We have separate detailed article on PODs – https://knowledge-junction.in/2022/05/05/kubernetes-pod/
• Replication Controller
  • Allows us to have multiple instances of single pod in Kubernetes cluster
  • Replication controller helps new pod instance in case existing pod fails
  • Itss make sure that at any given time specified number of Pods are running
• Replica Sets
  • Replica sets are the new way to maintain the replicas
  • Replica sets are replacement of Replication Controller
  • Replica set and Replication controller provide same set of functionality but replica set is more powerful
• Deployments
  • Object which represents our running application on cluster
  • Deployments are used to manages pods in Kubernetes cluster
  • Deployment object creates replica sets and number of pods as specified the value of replicas
• Services
  • Service object is logical set of Pod objects
  • Service object have unchanged ip address
  • Service object specifies how to access the respective Pods
  • Service object helps to connect in between applications, like if our application connects any external data source
  • It allows the connectivity between frontend and backend group of pods
  • Default protocol for services is TCP
• Ingress
  • Objects which allows access to Kubernetes services from outside the kubernetes cluster
  • This access is allowed via HTTP / HTTPs
• Volumes
  • Persistent storage used by Kubernetes to store the data stored in containers
  • Data is preserved across container restarts
  • Volume is a directory, possibly with some data in it, which is accessible to the containers in a pod
• ConfigMaps
  • Used to store non-confidential data in key value pair
  • ConfigMap does not provide secrecy or encryption
  • Used to store data separately from our application code
• Secrets
  • Used to store confidential data
  • Basically small amount of data like Password / Token or keys

How the Kubernetes objects are created

• Kubernetes objects can be created , modified or deleted with the help of Kubernetes APIs
• Mostly we / administrators uses kubectl command line utility tool
• Every object in Kubernetes have specification which tells Kubernetes system – the desired state of object
• Most of the time Kubernetes object specification is yaml file – to know more details about yaml files, please have a look of our detailed article – https://knowledge-junction.in/2021/09/04/complete-guide-to-yaml/

Thanks for reading the article !!! Please feel free to discuss in case any issues / suggestions / thoughts / questions !!!

HAVE A GREAT TIME AHEAD !!!