[TBD]Understanding kubernetes internals

Diagrams

Simplified flow of Kubernetes control plane and data plane(Ref here)

Learnings

• • Only Kube API-server interacts with etcd directly

  • No Kube infra component interact each other directly. All kube infra components (schedular, controller, Kubelet) interact with each-other via Kube API Server. So, Kube API Server acts as API Gateway

  • All kube infra component talk with each other via etcd

• Every component in Kubernetes (the API server, the scheduler, the kubelet, the controller manager, whatever) is stateless. All of the state is stored in a key-value store called etcd[https://jvns.ca/blog/2017/06/04/learning-about-kubernetes/]

  • In HA setup, each kube cluster has its own etcd

  • Etcd is no-sql database

• When a kubelet starts up, it registers itself as a node with the API server and starts watching for pods to run. [http://kamalmarhubi.com/blog/2015/09/06/kubernetes-from-the-ground-up-the-api-server/]

  • Kubelet reads about POD spec(with Nodename matching as its node) from etcd (via kube-apiserver) and creates it. [http://kamalmarhubi.com/blog/2015/09/06/kubernetes-from-the-ground-up-the-api-server/]

Sources: Meetup, personal experience

Reference

https://developer.ibm.com/opentech/2017/06/21/tour-kubernetes-source-code-part-one-kubectl-api-server/

https://jvns.ca/blog/2017/06/04/learning-about-kubernetes/

http://kamalmarhubi.com/blog/2015/08/27/what-even-is-a-kubelet/

http://kamalmarhubi.com/blog/2015/11/17/kubernetes-from-the-ground-up-the-scheduler/