Kubernetes Design Principles: Understand the Why

Kubecon Seattle 2018 Talk - https://sched.co/IrkE

Kubernetes is quickly becoming indispensable for managing and deploying workloads on distributed systems across both cloud and on-prem environments.

While most people are now familiar with how to use Kubernetes, few are aware of the “why” behind it? Why does the Kubernetes API look the way it does? Why do Kubernetes components only interact with each other through the Kubernetes API? Why is there a PersistentVolumeClaim object when you could easily reference a volume directly from a pod?

To answer these questions and help you develop a deeper understanding of Kubernetes, this talk exposes the principles underpinning the design of Kubernetes.

Transcript

1. Kubernetes Design Principles: Understand the Why
4. Node A Node B
5. Node A Node B Container A
6. Node A Node B Container A
7. Kubernetes APIs are declarative rather then imperative.
8. Before: You: System: You: After: You: System:
9. You: System: Master: API Server Node A Node B kubectl create -f replica.yaml
10. You: System: Master: API Server Node A Node B kubectl create -f replica.yaml apiVersion: apps/v1 kind: ReplicaSet metadata: name: frontend spec: replicas: 1 template: metadata: ... spec: ... containers: - name: nginx image: internal.mycorp.com:5000/mycontainer:1.7.9
11. You: System: Master: API Server Node A Node B Pod A definition
12. You: System: Master: API Server Node A Node B Pod A definition Pod A
14. Master: API Server Node A Node B Pod A definition Pod A
15. Master: API Server Node A Node B Pod A definition Pod A
16. kubectl create -f replica.yaml Master: API Server Node A Node B Pod A definition
17. Master: API Server Node A Node B Pod A definition
18. Master: API Server Node A Node B Pod A definition Pod A
19. Master: API Server Node A Node B Pod A definition Pod A
20. Master: API Server Node A Node B Pod A definition Pod A
21. The Kubernetes control plane is transparent. There are no hidden internal APIs.
22. Before: Master: Node: Master: After: Master: Node:
23. Master: API Server Node A Node B Master: Scheduler
24. Master: API Server Node A Node B Master: Scheduler kubectl create pod
25. Master: API Server Node A Node B Master: Scheduler Pod A definition
26. Master: API Server Node A Node B Master: Scheduler Pod A definition node: Node B
27. Master: API Server Node A Node B Master: Scheduler Pod A Pod A definition node: Node B
28. Master: API Server Node A Node B Master: Scheduler Pod A Pod A definition node: Node B kubectl delete pod A
29. Master: API Server Node A Node B Master: Scheduler Pod A
30. Master: API Server Node A Node B Master: Scheduler
34. Principle: Obvious solution: Master Node 1 API Server Scheduler Kubelet Watch for new Pods, scheduled to this node Docker Daemon Pod A node: Node1 Container for pod1 Fetch Secret Object Watch for new Pods
35. Meet the user where they are.
36. Before: After: Master Node 1 API Server Scheduler Kubelet Watch for new Pods, scheduled to this node Docker Daemon Pod A node: Node1 Container for pod1 Watch for new Pods Secret volume Fetch Secret file
38. Master Node 1 API Server Scheduler Kubelet Watch for new Pods, scheduled to this node Docker Daemon Pod A storage: gcePD1 Fetch Secret Object Watch for new Pods
39. Master Node 1 API Server Scheduler Kubelet Watch for new Pods, scheduled to this node Docker Daemon Pod A storage: gcePD1 node: Node1 Fetch Secret Object Watch for new Pods Schedule PodA to Node1
40. Master Node 1 API Server Kubelet Watch for new Pods, scheduled to this node Docker Daemon Pod A storage: gcePD1 node: Node1 Fetch Secret Object A/D Controller Watch for new Pods w/Volumes Storage Backend Attach gcePD1 to Node1
41. Master Node 1 API Server Kubelet Watch for new Pods, scheduled to this node Docker Daemon Pod A storage: gcePD1 node: Node1 Fetch Secret Object A/D Controller Watch for new Pods w/Volumes Storage Backend Attach gcePD1 to Node1 gcePD1
42. Master Node 1 API Server Kubelet Watch for new Pods, scheduled to this node Docker Daemon Pod A storage: gcePD1 node: Node1 Fetch Secret Object A/D Controller Watch for new Pods w/Volumes Storage Backend Attach gcePD1 to Node1 gcePD1 Container for pod1 Create container Mount volume
43. Master Node 1 API Server Kubelet Watch for new Pods, scheduled to this node Docker Daemon Pod A storage: gcePD1 node: Node1 Fetch Secret Object A/D Controller Watch for new Pods w/Volumes Storage Backend Attach gcePD1 to Node1 gcePD1 Container for pod1 Create container Mount volume
44. Workload portability
46. Master Node 1 API Server Kubelet Watch for new Pods, scheduled to this node Docker Daemon Pod A storage: pvc-a node: Node1 Container for pod1 gcePD1 A/D Controller Watch for new Pods w/Volumes Watch state of container pvc-a storage: pv-1 storageClass: storageClass1 pv-1 storage: gcePD1 StorageClass1 storage: gcePD Cluster admin facing API object User facing API object
47. Master Node 1 API Server Kubelet Watch for new Pods, scheduled to this node Docker Daemon Pod A storage: pvc-a node: Node1 Container for pod1 awsEBS1 A/D Controller Watch for new Pods w/Volumes Watch state of container pvc-a storage: pv-1 storageClass: storageClass1 pv-1 storage: awsEBS1 StorageClass1 storage: awsEBS Cluster admin facing API object User facing API object