Kubernetes basic building blocks

Building blocks of Kubernetes: 

• Pods
• ReplicaSets
• Deployments
• Namespaces

#Pods:

• wrapper around the container that kubernetes understands to maintain the cluster state. 
• Can run multiple containers. 
• Smallest and simplest unit of deployment object. 
• Pods
• sheduled on the same host
• Shares same network namespace
• Can run different configurations
• Homogeneous pods: multiple versions of the same deployment
• Heterogeneous pods: multiple pods of different configurations. 

#ReplicationController

• pod manager, Makes sure no. Of replicas in a pod is running as required. If less, it creates, if more it kills pods.

#ReplicaSets

• Next generation Replication controller that manages pod to maintain desired state. 
• Supports equolity and set based selectors. 

#Namespaces:

• Are used to group resources and assign privileges based on the namespaces.

#Labels and selectors: 

• Metadata can be assigned to pods or any objects as labels, ways by which you can glue multiple objects to gather. 
• These are used by kubernetes to perform operations to the group based on labels. 

#Services: 

• Are essentially endpoints by which pods communicate to other pods internally /externally (for example, web server / cache / db need to talk to each other)
• Exposed through endpoints (Internal and external). 
• Internal: example: don’t have to expose database to outside world, but accessible internally. 
• External: web UI to be exposed outside.