Kubernetes

https://kubernetes.io/

Production-grade container orchestration.

---

Components

Control plane

• etcd: distributed persistent storage (key/value)
• api server
• scheduler: in charge of placing different resources on different servers
• controller manager: manage controllers
• cloud controller manager: ensure the interactions with the cloud provider APIs

Worker nodes

• kubelet: in charge of creating and managing pods
• kubernetes proxy: redirection management
• container runtime: containers management

Architecture

Liveness vs Readiness

• a liveness will provoke a container reboot
• checks performed by the liveness probe: memory issue, dead lock, …
• checks performed by the readiness probe: check db connection, check external service connection, …

---
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: whoami
spec:
  replicas: 2
  selector:
    matchLabels:
      app: whoami
      level: expert
  template:
    metadata:
      labels:
        app: whoami
        level: expert
    spec:
      containers:
        - name: whoami
          image: containous/whoami:latest
          ports:
            - name: main-port
              containerPort: 80
          readinessProbe:
            httpGet:
              path: /health
              port: 80

Best practices

• use kubernetes deployment
• configure probes Startup, Readiness and Liveness
• use Init containers
• think twice before having kubernetes pods with multiple containers
• always set the ImagePullPolicy
• always set the Requests and Limits
• use labels and annotations
• use kubernetes as soon as possible
• version your descriptors

References

• training: https://github.com/l-lin/study/tree/master/kubernetes
• Introduction to Kubernetes Workshop | PPT
• DevJam 2019 - Introduction to Kubernetes | PPT
• Tutorials | Kubernetes
• Get Started with Kubernetes Ultimate Hands-on Labs and Tutorials | kubelabs
• 70 Best Kubernetes Tutorials
• Deploying a Spring Boot microservice in Kubernetes using Helm charts | by José Rodríguez | Medium