Cannot access ShinyProxy from remote workstation

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Summary

Accessing ShinyProxy from remote workstations fails despite correct Docker/WSL configurations and open ports? This occurs when Windows firewall rules block traffic between external devices and WSL-hosted ports. Unlike native ports, WSL requires explicit firewall allowances for remote access. This guide will resolve connectivity hurdles for Dockerized ShinyProxy deployments on Windows.

Root Cause

The issue stems from default Windows firewall rules that prohibit inbound connections to WSL-hosted applications. Key factors:

  • WSL operates as a virtualized network layer on Windows, isolated from host firewall exemptions.
  • Docker Desktop’s default rules apply to the DockerDesktop profile only, not WSL.
  • Explicitly allowing port 8080 via ufw in Ubuntu addresses Linux-side restrictions but ignores Windows network policies.

The critical gap: Ports forwarded by WSL aren’t automatically exposed to remote devices – Windows intercepts and blocks traffic unless specifically permitted.

Why This Happens in Real Systems

System complexity creates blind spots:

  1. Hybrid environments: WSL bridges Linux services to a Windows host, creating two network layers to configure.
  2. Default-insecure design: Consumer Windows installations default to blocking inbound connections unless explicitly allowed.
  3. Assumption gaps: Engineers often assume containerized apps behave identically across platforms, neglecting host OS policies.
  4. Silent failures: Firewalls drop packets without logging, masking the root cause during debugging.

Real-World Impact

Unaddressed, this issue causes:

  • Failure in demos/training: Team members can’t access locally hosted tools, disrupting workflows.
  • Delayed deployments: Engineers waste hours debugging networking instead of building features.
  • False blame cycles: Misattributing the problem to Docker/ShinyProxy rather than host policies.
  • Security risks: Workarounds like disabling firewalls expose systems to internal threats.

Example or Code

Symptomatic Configuration

This typical application.yml binds ShinyProxy globally but fails remotely due to Windows firewall: 

server:
  address: 0.0.0.0  # Binds to all interfaces (in WSL context)
  port: 8080
proxy:
  port: 8080
specs:
  - id: demo-app
    container-image: shiny-app:latest

Validation Steps:

  1. Confirm local host access works: 
    curl http://localhost:8080  # From WSL/PowerShell→ Success
  2. Test remote access (replace USER_IP): 
    curl http://192.168.1.100:8080  # Fails with timeout

How Senior Engineers Fix It

Step 1: Create a Windows Firewall Rule

Open PowerShell as Administrator and run: 

New-NetFirewallRule `
  -DisplayName "Allow WSL Port 8080" `
  -Direction Inbound `
  -Action Allow `
  -Protocol TCP `
  -LocalPort 8080

Step 2: Verify WSL Port Binding

In WSL (Ubuntu), check ShinyProxy binds externally: 

sudo netstat -tuln | grep 8080
# Should show: tcp6 0 0 :::8080 :::* LISTEN

Step 3: Disable Conflicting Rules

Ensure no other tools block access (e.g. VPNs, third-party firewalls).

Why This Works

The rule explicitly permits external devices to connect to port 8080 on the Windows host, bypassing default restrictions against WSL-sourced ports.

Why Juniors Miss It

Common oversights:

  1. Assumption bias: Belief that configuring Docker/WSL (e.g., address: 0.0.0.0) automatically covers host-level security.
  2. Toolchain focus: Over-reliance on Linux debugging tools (ufw, netstat) without checking Windows policies.
  3. Network misunderstanding: Treating WSL ports as equivalent to natively hosted Windows ports for firewall purposes.
  4. Documentation gaps: Most tutorials assume Linux hosts, neglecting Windows-specific layers.

Key Insight: Modern Windows acts as a hypervisor for WSL – remote traffic traverses two firewalls (Windows host + WSL guest), requiring layered configurations. Solve this by treating WSL-hosted services as VM workloads demanding host OS policy adjustments.

🔍 Troubleshooting Pro Tip: Test firewall impact by temporarily disabling Windows Defender Firewall. If connections succeed, firewall rules are the culprit.

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