Pods, Deployments and Services

📘What it really is

• A Pod is the smallest unit: one or more containers that run together on one node and share a network address. Usually one app container per pod. Pods are disposable, like containers.

• A Deployment keeps a number of identical pods running (through a ReplicaSet it manages) and handles updates.

• A Service gives a stable name and address to a changing set of pods, and spreads traffic across them. Types:
• ClusterIP (default): reachable only inside the cluster, by its name (for example routerani-api);

• NodePort and LoadBalancer: reachable from outside (a LoadBalancer service asks the cloud for a load balancer).

• Labels and selectors link them: pods carry app: routerani-api, and the Service's selector picks every pod with that label.

• Namespaces group resources (routerani-staging, routerani-prod) so names don't collide and permissions can differ.
• RouteRani as YAML (not verified): ```yaml apiVersion: apps/v1 kind: Deployment metadata: name: routerani-api spec: replicas: 2 selector: matchLabels: { app: routerani-api } template: metadata: labels: { app: routerani-api } spec: containers: - name: api image: routerani:1.0.3 ports: [{ containerPort: 3000 }] env: - { name: APP_VERSION, value: "1.0.3" }

apiVersion: v1 kind: Service metadata: name: routerani-api spec: selector: { app: routerani-api } ports: [{ port: 80, targetPort: 3000 }] ```

• Commands: kubectl apply -f routerani.yaml creates or updates; kubectl get deploy,pods,svc; kubectl describe pod <name> explains problems; kubectl logs <pod>; kubectl port-forward svc/routerani-api 8080:80 lets you test from your computer.