How to Configure Windows Sandbox Custom Host Resolution via Hosts File in Windows 11

When developing and testing web applications, microservices, or API integrations, software engineers frequently need to override domain name resolution to point production or staging hostnames (such as api.example.com or auth.corp.local) to local development servers or isolated test containers. Altering the primary hosts file on the Windows 11 host operating system is error-prone, risks unintended traffic redirection, and requires administrative privileges that are easily forgotten. Windows Sandbox configuration (.wsb) XML profiles allow developers to inject custom domain mappings into the sandbox’s disposable hosts file automatically without touching the host operating system.

Understanding Windows Sandbox Filesystem Isolation

Windows Sandbox boots from a pristine, dynamically generated Windows 11 base image. Key operating system files—including the TCP/IP hosts file at C:WindowsSystem32driversetchosts—are instantiated afresh upon each sandbox launch:

• C:WindowsSystem32driversetchosts: Maps IP addresses to hostnames prior to DNS resolver queries. Modifying this file inside the container redirects all browser, command-line, and application network traffic.
• <MappedFolder>: Safely shares host directories containing configuration assets into the sandbox as read-only volumes.
• <LogonCommand>: Executes automated PowerShell commands with elevated container privileges upon user session initialization.

Authoring the Windows Sandbox WSB Profile

Create a sandbox profile named Custom_Hosts_Sandbox.wsb on your Windows 11 host machine. This XML profile maps a local directory containing your custom domain mappings and launches the injection script upon startup:

<Configuration>
  <VGpu>Enable</VGpu>
  <Networking>Default</Networking>
  <MemoryInMB>6144</MemoryInMB>
  <MappedFolders>
    <MappedFolder>
      <HostFolder>C:SandboxAssetsHostsConfig</HostFolder>
      <SandboxFolder>C:HostsConfig</SandboxFolder>
      <ReadOnly>true</ReadOnly>
    </MappedFolder>
  </MappedFolders>
  <LogonCommand>
    <Command>powershell.exe -ExecutionPolicy Bypass -NoExit -File C:HostsConfigInject-Hosts.ps1</Command>
  </LogonCommand>
</Configuration>

Authoring the Hosts Injection PowerShell Script

In directory C:SandboxAssetsHostsConfig on your host, create custom_hosts.txt containing the desired IP-to-hostname mappings:

# Staging and Mock Environment Mappings
10.0.1.15       api.example.com
10.0.1.16       auth.corp.local
127.0.0.1       mock-payment.internal

In the same folder, create the automation bootstrap script named Inject-Hosts.ps1:

Write-Host "Configuring Windows Sandbox Custom Domain Resolution..." -ForegroundColor Cyan

$SourceHosts = "C:HostsConfigcustom_hosts.txt"
$TargetHosts = "C:WindowsSystem32driversetchosts"

if (Test-Path $SourceHosts) {
    Write-Host "Appending custom domain mappings to container hosts file..." -ForegroundColor Green
    
    # Read custom entries and append to the container hosts file
    $Entries = Get-Content -Path $SourceHosts -Raw
    Add-Content -Path $TargetHosts -Value ""
    Add-Content -Path $TargetHosts -Value "# --- Windows Sandbox Custom Mappings ---"
    Add-Content -Path $TargetHosts -Value $Entries
    
    # Flush Windows DNS Resolver Cache
    Write-Host "Flushing DNS resolver cache..." -ForegroundColor Yellow
    Clear-DnsClientCache
    
    Write-Host "Custom hosts injected successfully!" -ForegroundColor Green
} else {
    Write-Error "Custom hosts template file not found at $SourceHosts"
}

# Display active hosts file contents for verification
Write-Host "Current Sandbox Hosts File Contents:" -ForegroundColor Cyan
Get-Content -Path $TargetHosts | Write-Host

# Test resolution with Resolve-DnsName
Write-Host "Testing hostname resolution for api.example.com:" -ForegroundColor Yellow
ping.exe -n 1 api.example.com | Write-Host

Launching and Testing Domain Redirection

1. Double-click Custom_Hosts_Sandbox.wsb on your Windows 11 host.
2. Windows Sandbox spins up in a disposable desktop window within seconds.
3. The PowerShell window opens automatically upon logon, appends the custom records to C:WindowsSystem32driversetchosts, flushes the DNS cache, and executes a ping test confirming that api.example.com resolves to 10.0.1.15.
4. Launch Microsoft Edge inside the sandbox and navigate to http://api.example.com to interact with your testing endpoint.
5. Close Windows Sandbox when testing is complete. The container is destroyed, leaving your host machine’s network stack and hosts file entirely untouched.