CKA Notes

Studying for the CKA exam, wanted to keep some notes I found helpful that I might polish up later for others to enjoy. These include analogies, visualizations, explanations, etc.

Master / Control Plane (cp)

Cluster Store

• Key/value store for cluster
• Stores current state
• Typically etcd

Controller vs Controller Manager

• Controller - keeps asking the same question to its appropriate subordinate resources. Think “mum?” gif from Family Guy. Controller runs in infinite control loops.
• Controller Manager - keeps track of changes in responses received by controllers and communicates changes to apiserver. Helps maintain desired state.

Scheduler

• Watches apiserver for new pods
• Assigns work to nodes based on availability
• Respects constraints

API Server

• RESTful
• Single, central intermediary for all other cp services

Nodes (Workers/Minions)

kubelet

• Main k8s agent inside a node, must run as long as node runs
• Watches API server
• Instantiates pods
• Reports back to master
• Exposes endpoint on port 10255

Container Engine

• Manages containers (pulling images, starting/stopping containers)
• Usually Docker, can be others

kube-proxy

If Kubernetes were a person (stage crew)

Cast

• K8s admin = stage director

Admin: [finishes writing a letter] Done. [Hands letter to API server]

API Server: [reads letter, ]

Controllers:

Replication Controllers

Ensures specified number of pods are running