Kubernetes Master

• Kubernetes master runs on Linux nodes

Master Components

kube-apiserver

• This component is Central to Kubernetes. All communications between all components goes through the kube-apiserver
• This component is frontend of the Kubernetes control plane.
• This component exposes a REST API.
• We would interact with this component using kubectl by using the YAML files, which are also referred as manifests

etcd

• etcd stores the entire configuration and the state of the cluster.
• etcd is consistent and highly available distributed key-value store.

kube-scheduler

• It watches for new work tasks and assigns them to healthy nodes in the cluster

Controller-Manager

• It is responsible for maintaining desired states mentioned in the manifest.
• It looks like single component, but with in it has
  • Node Controller: for noticing & responding when node goes down
  • Replication Controller: for maintaining the correct number of pods for every replication controller object.
  • Endpoints Controller: Populates the Endpoints object

Cloud-Controller-manager

• If you run the Kubernetes on a supported cloud platform such as AWS, Azure or Google, your control plane runs the Cloud-Controller-Manager.
• It is responsible for underlying cloud specific controllers.

Node Components

kubelet

• This is an agent which runs on each node in the cluster.
• It watches for the instructions from API Server for new work assignments.
• If it can’t run the task assigned, it reports back to master and lets control plane decide on the actions.
• It is responsible for the node registration process

Container Runtime

• This is software which is responsible for running containers.
• Some of them are Docker, containerd, cri-o, rktlet

kube-proxy

• Maintains the network rules on nodes
• This is responsible for networking on nodes.

Cluster DNS

• Every Kubernetes Cluster has an internal DNS service
• This has static IP address that is hardcoded into every Pod on the cluster i.e. all Pods now how to find the DNS Server
• Services, Stateful Sets and Pods are registered with Cluster DNS.
• Cluster DNS is based on CoreDNS

Interesting ADD ONS

Web UI (Dashboard)

• Web based Kubernetes user interface
• Capabilities:
  • Deployment
  • View cluster resources
  • Troubleshooting

Container Resource Monitoring

• We will discuss about it in next series of articles

Cluster Level Logging

• We will discuss about it in next series of articles

How to Package Apps To Run on Kubernetes

• Package your application as container image.
  • We would create a Image for the application
  • Push the image to Docker Registry
• Pod will Wrap container
• Pod is deployed into Kubernetes cluster via Declarative Manifest file.