> ## Documentation Index
> Fetch the complete documentation index at: https://docs.microsandbox.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Create an ephemeral preview deploy

> Serve a built site from a time-limited microVM

<Tooltip tip="This workflow depends on publishing a guest service to a port on the computer running the CLI, which is not available on microsandbox cloud."><span className="msb-badge-local">Local-only <Icon icon="circle-info" size={11} /></span></Tooltip>

Copy a static build into a microVM, expose it on host loopback, and let the sandbox expire automatically. The preview cannot modify the host build or make outbound network requests.

## Run the preview

<Steps>
  <Step title="Start the preview">
    Run this after producing `dist`:

    <CodeGroup>
      ```sh macOS & Linux theme={null}
      msb run -d --name preview --replace \
        --memory 256M --max-duration 30m --copy-dir ./dist:/site \
        -p 127.0.0.1:4173:8080 \
        --net-default-egress deny --net-default-ingress allow \
        --security restricted --user 65534:65534 \
        python:3.13.14-alpine3.23 -- python -m http.server 8080 \
          --bind 0.0.0.0 --directory /site
      ```

      ```powershell Windows theme={null}
      msb run -d --name preview --replace `
        --memory 256M --max-duration 30m --copy-dir ./dist:/site `
        -p 127.0.0.1:4173:8080 `
        --net-default-egress deny --net-default-ingress allow `
        --security restricted --user 65534:65534 `
        python:3.13.14-alpine3.23 -- python -m http.server 8080 `
          --bind 0.0.0.0 --directory /site
      ```
    </CodeGroup>

    Detached runs return before the server is ready. Wait for it, then open the preview:

    <CodeGroup>
      ```sh macOS & Linux theme={null}
      until curl -fsS http://127.0.0.1:4173/ >/dev/null 2>&1; do sleep 1; done
      ```

      ```powershell Windows theme={null}
      do {
        curl.exe -fsS http://127.0.0.1:4173/ *> $null
        if ($LASTEXITCODE -ne 0) { Start-Sleep -Seconds 1 }
      } until ($LASTEXITCODE -eq 0)
      ```
    </CodeGroup>

    Open the preview after the readiness check succeeds:

    <CodeGroup>
      ```sh macOS & Linux theme={null}
      open http://127.0.0.1:4173
      ```

      ```powershell Windows theme={null}
      Start-Process http://127.0.0.1:4173
      ```
    </CodeGroup>

    On Linux, replace `open` with `xdg-open`, or visit the URL manually.

    `--copy-dir` gives the guest its own copy of `dist`. Use a unique sandbox name and host port for each concurrent pull request.

    <Warning>
      Loopback is not authentication: other processes on the host can reach the preview. Browser JavaScript is also outside the guest network policy, so review untrusted builds with a disposable browser profile.
    </Warning>
  </Step>

  <Step title="Clean up">
    ```sh theme={null}
    msb rm -f preview
    ```

    `--max-duration 30m` still removes an abandoned preview when explicit cleanup does not run.
  </Step>
</Steps>