Spring Boot: Resolving Config Server Connection Timeout Due to Service Port Mismatch in Kubernetes

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I have two Spring Boot applications running in the same Kubernetes namespace (kubernetes-learning): one is the config-server and the other is the business-logic-app that consumes data from the config-server. The config-server container listens on port 8888, but its Service is exposing port 80. Meanwhile, the business-logic-app is configured to connect using port 8888 (SPRING_CLOUD_CONFIG_URI=http://kubernetes-learning-config-server:8888), leading to a connection timeout which causes livenessProbe and readinessProbe failures.

Below are the relevant configurations:

config-server.yaml

YAML
# Config server
apiVersion: apps/v1
kind: Deployment
metadata:
  name: kubernetes-learning-config-server
  namespace: kubernetes-learning
  labels:
    app: kubernetes-learning-config-server
spec:
  replicas: 2
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 1
  selector:
    matchLabels:
      app: kubernetes-learning-config-server
  template:
    metadata:
      name: kubernetes-learning-config-server
      labels:
        app: kubernetes-learning-config-server
    spec:
      containers:
        - name: kubernetes-learning-config-server
          image: ghcr.io/kubernetes/learning.config-server
          imagePullPolicy: Always
          ports:
            - containerPort: 8888
              protocol: TCP
            - containerPort: 48888
              protocol: TCP
          env:
            - name: BPL_JVM_THREAD_COUNT
              value: "50"
            - name: BPL_DEBUG_ENABLED
              value: "true"
            - name: BPL_DEBUG_PORT
              value: "48888"
            - name: GITHUB_CONFIG_DATA_URL
              value: https://github.com/kubernetes/config-data
            - name: GITHUB_CONFIG_DATA_USERNAME
              value: github_user
            - name: GITHUB_CONFIG_DATA_PERSONAL_ACCESS_TOKEN
              value: github_sampletoken  
          livenessProbe:
            httpGet:
              path: /alpha-app/local
              port: 8888
            initialDelaySeconds: 30
            periodSeconds: 20
            timeoutSeconds: 10
            successThreshold: 1
            failureThreshold: 3
          readinessProbe:
            httpGet:
              path: /alpha-app/local
              port: 8888
            initialDelaySeconds: 30
            periodSeconds: 20
            timeoutSeconds: 10
            successThreshold: 1
            failureThreshold: 3

      restartPolicy: Always

# Expose Config server
---
apiVersion: v1
kind: Service
metadata:
  name: kubernetes-learning-config-server
  labels:
    app: kubernetes-learning-config-server
spec:
  type: ClusterIP
  selector:
    app: kubernetes-learning-config-server
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8888

alpha-app.yaml

YAML
# app applications
apiVersion: apps/v1
kind: Deployment
metadata:
  name: kubernetes-learning-app
  namespace: kubernetes-learning
  labels:
    app: kubernetes-learning-app
spec:
  replicas: 1
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 1
  selector:
    matchLabels:
      app: kubernetes-learning-app
  template:
    metadata:
      name: kubernetes-learning-app
      labels:
        app: kubernetes-learning-app
    spec:
      containers:
        - name: kubernetes-learning-alpha-app
          image: ghcr.io/kubernetes/learning.alpha-app
          imagePullPolicy: Always
          ports:
            - containerPort: 8441
              protocol: TCP
            - containerPort: 48441
              protocol: TCP
          env:
            - name: BPL_JVM_THREAD_COUNT
              value: "50"
            - name: BPL_DEBUG_ENABLED
              value: "true"
            - name: BPL_DEBUG_PORT
              value: "48441"
            - name: SPRING_PROFILES_ACTIVE
              value: kube
            - name: SPRING_CLOUD_CONFIG_FAIL_FAST
              value: "true"
            - name: SPRING_CLOUD_CONFIG_RETRY_INITIAL_INTERVAL
              value: "1000"
            - name: SPRING_CLOUD_CONFIG_RETRY_MAX_INTERVAL
              value: "10000"
            - name: SPRING_CLOUD_CONFIG_RETRY_MULTIPLIER
              value: "2"
            - name: SPRING_CLOUD_CONFIG_RETRY_MAX_ATTEMPTS
              value: "5"
            - name: SPRING_CLOUD_CONFIG_URI
              value: http://kubernetes-learning-config-server:8888
          livenessProbe:
            httpGet:
              path: /info
              port: 8441
            initialDelaySeconds: 60
            timeoutSeconds: 15
            periodSeconds: 30
            successThreshold: 1
            failureThreshold: 3
          readinessProbe:
            httpGet:
              path: /info
              port: 8441
            initialDelaySeconds: 60
            timeoutSeconds: 15
            periodSeconds: 30
            successThreshold: 1
            failureThreshold: 3

      restartPolicy: Always


# Expose Config server
---
apiVersion: v1
kind: Service
metadata:
  name: kubernetes-learning-app
  labels:
    app: kubernetes-learning-app
spec:
  type: ClusterIP
  selector:
    app: kubernetes-learning-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8441

The exception indicates a timeout when accessing:

JAVA
Caused by: org.springframework.web.client.ResourceAccessException: I/O error on GET request for "http://kubernetes-learning-config-server:8888/alpha-app/kube": Connect timed out
    at ...

I've already tried redeploying both apps. What adjustments should I make to resolve this connectivity issue?

Comments 0

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Answers 2

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2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

The problem is that the business-logic-app is trying to connect to your config-server on port 8888, while the Service exposing the config-server is configured on port 80. In Kubernetes, when a Service maps traffic, the port you need to use when contacting the Service is the Service’s port—not the container’s targetPort.

What’s Happening

In your config-server deployment, the container listens on port 8888.
Your Service for the config-server maps port 80 to container port 8888.
The business-logic-app’s environment variable SPRING_CLOUD_CONFIG_URI is set to use port 8888 (http://kubernetes-learning-config-server:8888), so the connection request never reaches the Service correctly, resulting in a timeout.

How to Fix It

You have two options:

Update the Business-Logic-App Configuration:
Change the SPRING_CLOUD_CONFIG_URI to point to the Service’s port 80. For example:
```
YAML
- name: SPRING_CLOUD_CONFIG_URI
  value: http://kubernetes-learning-config-server:80
```

Update the Config-Server Service:
Change the Service definition so that it exposes port 8888 instead of 80. For example:

YAML
apiVersion: v1
kind: Service
metadata:
  name: kubernetes-learning-config-server
  labels:
    app: kubernetes-learning-config-server
spec:
  type: ClusterIP
  selector:
    app: kubernetes-learning-config-server
  ports:
    - protocol: TCP
      port: 8888         # Expose port 8888
      targetPort: 8888   # Target container’s port 8888

Additional Considerations

Ensure that both the deployments and services are in the same namespace. You already confirm they are in kubernetes-learning, so that's correct.
The failing liveness and readiness probes are likely a consequence of the application failing to retrieve configuration at startup, causing cascading failures.

Choose one of the options above to ensure that your business-logic-app connects to the correct port exposed by the Service.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

No comments yet.

Answer by JovianRanger540 • 1 month ago

That is because the service is listening on port 80 that will be routed to port 8888 on the target pods.

YAML
ports:
  - protocol: TCP
    port: 80
    targetPort: 8888

Therefore, you need to point kubernetes-learning-app to http://kubernetes-learning-config-server:80/alpha-app/kube.

N.B. as mentioned by a comment to the question, http://kubernetes-learning-config-server works too because an http:// URL without port number will default to port 80 which coincidentally what you have set as the service port, not because the service decides the port. Should you use another port like 8080, the URL without a port number would not work.

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Spring Boot: Resolving Config Server Connection Timeout Due to Service Port Mismatch in Kubernetes

2 Answers

What’s Happening

How to Fix It

Additional Considerations

Discussion

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