Add Windows service registration support to azure-cns

[Copilot]

Overview

This PR adds Windows service registration support to azure-cns, enabling it to self-register as a Windows service for automatic startup and recovery. This addresses the requirements from the Azure Batch team who need azure-cns to automatically restart on crashes and start automatically when VMs reboot.

Changes

Core Implementation

• Windows Service Handler (cns/service/service_windows.go): Implements Windows service functionality using golang.org/x/sys/windows/svc package

  • Service installation with automatic startup configuration
  • Service uninstallation with graceful shutdown
  • Windows Service Control Manager integration
  • Event log integration for service lifecycle events
  • Auto-recovery configuration (5-second restart delays, 3 attempts, 24-hour reset)

• Platform Stub (cns/service/service_other.go): Non-Windows platforms return appropriate errors when service operations are attempted

• Service Integration (cns/service/main.go):

  • Added --service command-line flag with install, uninstall, and run actions
  • Automatic detection when started by Windows Service Manager
  • Graceful handling of service stop/shutdown requests

• Configuration (common/config.go): Added service-related command-line option constants

Testing

• Unit Tests (cns/service/service_test.go): Tests for service functions on non-Windows platforms
• All existing tests pass
• Binary builds successfully on Linux

Documentation

• CNS README (cns/README.md): General documentation with Windows service overview
• Windows Service Guide (cns/doc/windows-service.md): Comprehensive guide including:
  • Installation and configuration instructions
  • Service management using PowerShell and Windows tools
  • Troubleshooting section
  • Event log monitoring examples
  • Command reference

Usage

Install and Start Service

# Install as Windows service (requires Administrator privileges)
azure-cns.exe --service install

# Start the service
net start azure-cns

# Verify status
Get-Service azure-cns

View Service Logs

Get-EventLog -LogName Application -Source azure-cns -Newest 20

Uninstall Service

net stop azure-cns
azure-cns.exe --service uninstall

Service Configuration

The service is registered with the following settings:

• Service Name: azure-cns
• Display Name: Azure Container Networking Service
• Start Type: Automatic
• Service Account: LocalSystem
• Recovery Actions: Restart after 5 seconds on failure (3 attempts)

Benefits

1. Automatic Startup: Service starts automatically on system boot
2. Self-Recovery: Automatic restart when the process crashes
3. Standard Management: Works with native Windows service tools (services.msc, net.exe, PowerShell)
4. Event Logging: Lifecycle events logged to Windows Event Log
5. No External Dependencies: Self-registration without requiring NSSM or other tools

Platform Compatibility

• Windows: Full service registration and management support
• Linux: Service operations return appropriate errors (use systemd or other init systems)

Testing Notes

• ✅ Builds successfully on Linux
• ✅ All existing tests pass
• ✅ New unit tests pass
• ✅ No breaking changes
• ⏳ Manual Windows testing recommended before deployment

Fixes #[issue_number]

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Azure CNS] Register azure-cns as windows service</issue_title>
<issue_description>Azure Batch team uses Azure-CNS for ADF works. We run azure-cns.exe (only windows) as standalone executable at individual VM.

However, we need register azure-cns.exe as windows service so it will restart when it crashes or start automatically when VM reboot.

We would like the feature for azure-cns to add a new flag which can register itself as windows service.</issue_description>

<agent_instructions>Learn about best practices related to apps registering as a Windows service and how that could be implemented in CNS. If apps typically don't register themselves and that is an orchestrator's responsibility, take no action.
</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@rbtr @xingwu1 I'm not familiar with Windows services. Is it typical for the executable to register _itself_ as a Windows service? That seems like something that an orchestrator would manage. If this is the standard, feel free to open a PR to add this support.

Fixes #4046

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