Rancher Desktop v1.13.1 - Port Forwarding not binding to ipv4 in MacOS

[dcardozo]

I'm using Rancher Desktop v1.13.1 in a MacBook Pro (m1) running MacOS 14.3.1. I've deployed a Java application in kubernetes and enabled port forwarding via the Rancher Desktop UI.

Trying to connect to the service from a Java client application in the localhost is met with a connection refused message; if I disable port forwarding via UI and enable it via kubectl, it works fine. The output of netstat shows that forwarding via the UI binds the port to ipv6 only, while forwarding via kubectl binds the port to both ipv4 and ipv6.

In version 1.11.1, port forwarding via the UI bound the port to ipv4 only.

Questions:

1. Is the change in behavior intentional? i.e. Rancher Desktop 1.11.1 binding to ipv4 only and 1.13.1 binding to ipv6 only.
2. Is there any available setting in Rancher Desktop that would allow binding ports to both ipv4 and ipv6 (same as kubectl port-forward)?
3. Alternatively, is there a setting to allow reverting back to version 1.11.1 behavior?

Thank you in advance for any guidance you may provide,

David

---

I've provided a simple Java Socket program to illustrate the issue:

SimpleServer.java:

import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class SimpleServer {
    public static void main(String[] args) {
        int port = 8000;

        try (ServerSocket serverSocket = new ServerSocket(port)) {
            System.out.println("Server is listening on port " + port);

            while (true) {
                try (Socket socket = serverSocket.accept()) {
                    System.out.println("New client connected");

                    OutputStream outputStream = socket.getOutputStream();
                    outputStream.write("success".getBytes());
                    outputStream.flush();
                } catch (Exception e) {
                    System.err.println("Error handling client connection: " + e.getMessage());
                }
            }
        } catch (Exception e) {
            System.err.println("Server error: " + e.getMessage());
        }
    }
}

SimpleClient.java

import java.io.InputStream;
import java.net.Socket;

public class SimpleClient {
    public static void main(String[] args) {
        String host = "localhost";
        int port = 8000;

        try (Socket socket = new Socket(host, port)) {
            InputStream inputStream = socket.getInputStream();
            byte[] buffer = new byte[7]; // "success" is 7 bytes long
            int read = inputStream.read(buffer);
            String message = new String(buffer, 0, read);

            System.out.println("Received message: " + message);
        } catch (Exception e) {
            System.err.println("Client error: " + e.getMessage());
        }
    }
}

Dockerfile

# Stage 1: Build the Java application
FROM openjdk:11-jdk-slim AS build

# Set the working directory inside the build container
WORKDIR /app

# Copy the Java source code to the build container
COPY SimpleServer.java /app

# Compile the Java source code
RUN javac SimpleServer.java

# Stage 2: Create the final runtime image
FROM openjdk:11-jre-slim

# Set the working directory inside the runtime container
WORKDIR /app

# Copy the compiled class file from the build container
COPY --from=build /app/SimpleServer.class /app

# Expose port 8000 for the application
EXPOSE 8000

# Run the SimpleServer application
CMD ["java", "SimpleServer"]

simple-server.yml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: simple-server-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: simple-server
  template:
    metadata:
      labels:
        app: simple-server
    spec:
      containers:
        - name: simple-server
          image: test/simple-server:1.0.0
          ports:
            - containerPort: 8000
---
apiVersion: v1
kind: Service
metadata:
  name: simple-server-service
spec:
  selector:
    app: simple-server
  ports:
    - protocol: TCP
      port: 8000
      targetPort: 8000
  type: ClusterIP

Here are the steps to reproduce and the output:

Build image: docker build -t test/simple-server:1.0.0 .
Compile client program: javac SimpleClient.java

Test 1

Run as a simple container: docker run --rm -p 8000:8000 test/simple-server:1.0.0
Run client: java SimpleClient
Output: Received message: success
netstat output:

❯ netstat -an | grep 8000
tcp4       0      0  *.8000                 *.*                    LISTEN
tcp4       0      0  127.0.0.1.8000         127.0.0.1.49605        TIME_WAIT

Test 2

Deploy in kubernetes: kubectl apply -f simple-server.yml
Enable port forwarding via Rancher Desktop UI
Run client: java SimpleClient
Output: Client error: Connection refused
netstat output:

❯ netstat -an | grep 8000
tcp6       0      0  ::1.8000               *.*                    LISTEN

Test 3

Stop port forwarding in the UI, enable port forwarding via kubectl: kubectl port-forward services/simple-server-service 8000:8000
kubectl output:

Forwarding from 127.0.0.1:8000 -> 8000
Forwarding from [::1]:8000 -> 8000

Run client: java SimpleClient
Output: Received message: success
netstat output:

❯ netstat -an | grep 8000
tcp6       0      0  ::1.8000               *.*                    LISTEN
tcp4       0      0  127.0.0.1.8000         *.*                    LISTEN
tcp4       0      0  127.0.0.1.49723        127.0.0.1.8000         TIME_WAIT

---

Downgrading to Rancher Desktop v1.11.1 allows me to enable port forwarding via the UI and connect successfully:

Test 1

Same behavior as in Rancher Desktop v1.13.1

Test 2

Deploy in kubernetes: kubectl apply -f simple-server.yml
Enable port forwarding via Rancher Desktop UI
Run client: java SimpleClient
Output: Received message: success
netstat output:

❯ netstat -an | grep 8000
tcp4       0      0  127.0.0.1.8000         *.*                    LISTEN
tcp4       0      0  127.0.0.1.49350        127.0.0.1.8000         TIME_WAIT

Test 3

Same behavior as in Rancher Desktop v1.13.1