I’m new to Kubernetes (K8S) and trying to learn how to achieve zero downtime during deployments. I have two services: currency-exchange and currency-conversion, where currency-conversion depends on currency-exchange.

When I deploy a new version of currency-exchange, the old pod stops immediately, causing an internal server error since the new pod isn’t ready yet. To prevent this, I added Readiness and Liveness probes to the deployment YAML so that Kubernetes checks the pod’s health before terminating the old one. My understanding is that this should help maintain zero downtime.

The Issue: When I add both the Liveness and Readiness probes, the new pod fails to start correctly and enters a CrashLoopBackOff state after multiple restarts.

this is my deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  annotations:
    deployment.kubernetes.io/revision: "1"
  labels:
    app: currency-exchange
  name: currency-exchange
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: currency-exchange
  strategy:
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25%
    type: RollingUpdate
  template:
    metadata:
      labels:
        app: currency-exchange
    spec:
      containers:
        - image: username_24/currency-exchange-service:0.0.11-SNAPSHOT
          imagePullPolicy: IfNotPresent
          name: mmv2-currency-exchange-service
          readinessProbe:
            httpGet:
              port: 8000
              path: /actuator/health/readiness
          livenessProbe:
            httpGet:
              port: 8000
              path: /actuator/health/liveness
          resources:
            limits:
              cpu: 500m
              ephemeral-storage: 1Gi
              memory: 2Gi
            requests:
              cpu: 500m
              ephemeral-storage: 1Gi
              memory: 2Gi
      restartPolicy: Always
---
apiVersion: v1
kind: Service
metadata:
  labels:
    app: currency-exchange
  name: currency-exchange
  namespace: default
spec:
  ports:
    - port: 8000
      protocol: TCP
      targetPort: 8000
  selector:
    app: currency-exchange
  sessionAffinity: None
  type: LoadBalancer

this is the related props in the application.properties

## Activate the health probes (liveness and readiness) to avoid downtime
management.endpoint.health.probes.enabled=true
management.health.livenessState.enabled=true
management.health.readinessState.enabled=true

What I’ve Tried: I tried removing the Liveness probe and using only the Readiness probe. This seems to work fine, and there is no downtime during deployment. However, I need to understand why the pod fails and enters CrashLoopBackOff when the Liveness probe is enabled.

Any insights into what might be going wrong or how to properly configure these probes to avoid downtime would be greatly appreciated!