How to Fix Docker 404 Not Found on Kubernetes Pod

Troubleshooting: “Docker 404 Not Found” on Kubernetes Pod

When encountering a “Docker 404 Not Found” error within a Kubernetes Pod context, it’s crucial to understand that the HTTP 404 status code is almost invariably returned by the application inside your container, not by the Docker daemon itself. This issue commonly signals an application-level misconfiguration where the requested API endpoint or resource path does not exist, or the application is not listening on the expected port or path as defined by its internal configuration or external Kubernetes services.

1. The Root Cause

A “Docker 404 Not Found” error originating from a Kubernetes Pod signifies that the application running within the container is returning an HTTP 404 status code, not the Docker daemon itself. This typically indicates an incorrect API endpoint path requested, or the application’s internal routing is misconfigured and doesn’t expose the expected resource.

2. Quick Fix (CLI)

Begin by inspecting the pod’s state and accessing the application internally to pinpoint the issue.

  1. Inspect Pod Logs and Events: Check for application-specific errors related to routing or startup failures.

    kubectl logs <your-pod-name> -n <your-namespace>
kubectl describe pod <your-pod-name> -n <your-namespace>

  2. Test Application Endpoint Internally (if pod is running): Execute a shell inside the container and attempt to curl the application directly to confirm its internal responsiveness and exposed paths. Replace <application-port> with the port your application listens on (e.g., 8080) and <expected-path> with the path you expect to reach (e.g., /api/v1/health).

    kubectl exec -it <your-pod-name> -n <your-namespace> -- /bin/bash
# Once inside the container:
curl localhost:<application-port>/<expected-path>
# Example: curl localhost:8080/api/v1/users
# Exit the container: exit

    If curl also returns a 404 or fails, the issue is likely within the application’s internal routing or its startup process.

3. Configuration Check

Review your Kubernetes resource definitions and the application’s internal configuration.

  1. Deployment Configuration (Deployment.yaml):

    • Verify the containerPort matches the port your application actually listens on inside the container.
    # Example snippet in your Deployment.yaml
spec:
  template:
    spec:
      containers:
      - name: your-app-container
        image: your-image:latest
        ports:
        - containerPort: 8080 # Ensure this matches your application's listening port
        # ... other configurations like args, env, volumeMounts ...

  2. Service Configuration (Service.yaml):

    • Ensure the targetPort in your Service definition correctly maps to the containerPort defined in your Deployment. Also, confirm the selector matches your pod’s labels.
    # Example snippet in your Service.yaml
spec:
  ports:
  - protocol: TCP
    port: 80 # The port the Service exposes (often 80 or 443)
    targetPort: 8080 # This MUST match your containerPort from Deployment
  selector:
    app: your-app # Ensure this selector matches labels on your pods

  3. Ingress Configuration (Ingress.yaml) (if applicable):

    • If using an Ingress, confirm the path and service.port.number correctly route to your Service and its exposed path. Misconfigured Ingress paths are a common source of external 404s.
    # Example snippet in your Ingress.yaml
spec:
  rules:
  - host: your.domain.com
    http:
      paths:
      - path: /api(/.*)? # Ensure this regex/path matches your application's routes
        pathType: Prefix # Or ImplementationSpecific, Exact
        backend:
          service:
            name: your-service-name
            port:
              number: 80 # This MUST match your Service's 'port'

  4. Application Configuration:

    • If your application uses environment variables or a configuration file to define its base path, API endpoints, or routing, verify these are correctly set within the container. This often means checking env variables in your Deployment.yaml or inspecting the Dockerfile/image build process.

4. Verification

After applying any fixes, verify the application’s responsiveness.

  1. Test via Port Forwarding (for Services): Temporarily expose your service locally to test its direct response.

    kubectl port-forward service/<your-service-name> <local-port>:<service-port> -n <your-namespace>
# Example: kubectl port-forward service/my-app-service 8080:80 -n default
# Open a new terminal and run:
curl http://localhost:<local-port>/<expected-path>

  2. Test Ingress Endpoint (for Ingress):

    curl http://<your-ingress-host>/<expected-path>

    A successful 200 OK response indicates the issue has been resolved. If the 404 persists, re-evaluate application logs for deeper internal routing problems.

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