FluxDeployDocs
Topics: Boot Images

Boot Images

Boot images are WinPE-based ISOs (or WIM files) that contain the FluxDeploy agent. They are the mechanism by which target machines boot into the deployment environment, either via PXE network boot or USB media.

Building an Image

Navigate to Boot Images and click Build New Image. The dialog asks for two things:

  • Name - required
  • Locale - the bcdboot /l parameter for boot manager language (e.g. en-US)

A summary line underneath says what the build will pick up: how many WinPE drivers (all active ones are embedded automatically), which WinPE packages, and which size optimizations. Those defaults live in Settings > Deployment > Boot Image. Server URL and TLS thumbprint are not asked for either - they are set per deployment target (Core and each relay) at build time.

The build job is processed by the BootImageBuildService background service, which invokes the IsoBuilder CLI. The list above the table shows the WinPE driver count and the PXE-active image, and links to the WinPE drivers page.

A boot image's detail page has a Build Log tab. While the image is still building, that tab refreshes itself every 5 seconds and says so, so watching a build no longer means pressing Refresh. The ISO and WIM output paths are listed with the rest of the build configuration rather than in a panel of their own.

Build Process

The IsoBuilder performs these steps:

  1. Copy WinPE base files from the Windows ADK staging directory
  2. Mount boot.wim via DISM
  3. Inject default WinPE packages: WMI, NetFx, Scripting, PowerShell
  4. Inject the .NET 10 agent (self-contained, trimmed) to X:\Deploy\
  5. Embed selected WinPE drivers to X:\WinPEDrivers\
  6. Write startnet.cmd (wpeinit + agent launch)
  7. Embed agent.config.json with server URL, TLS thumbprint, and the shared agent bearer token (see Authentication - the token is the same in every boot image and readable by anyone who can pull the image over TFTP)
  8. Unmount and commit the WIM
  9. Create the ISO via oscdimg.exe

PXE Activation

Each boot image has an IsPxeActive flag. Only one image can be active for PXE at a time. When activated:

  • The boot WIM is copied to the PXE boot files directory
  • PXE BCD is generated referencing the new boot WIM
  • Relay boot image builds are automatically enqueued for all online relay sites

Manual Boot (testing without PXE)

Every completed boot image can be downloaded as bootable media from Boot Images > Actions > Manual Boot ISO - one entry per server, including each relay site, because the server address and certificate thumbprint are written into the boot image at build time and an ISO reaches only the server it was built for. A site's ISO is generated by that relay as you download it and stored nowhere. See Manual Boot ISOs for the whole story: which entry to pick, what the filename tells you, why a site might not be able to produce one, the 4 GiB limit, and who may download them.

Relay Auto-Sync

When a boot image is activated on Core, RelayBootImageService creates RelayBootImage build jobs for each relay site. These use the --wim-only flag (faster, smaller output). Each relay build embeds the relay's own URL and TLS certificate thumbprint so agents at that site connect to their local relay.

Relay heartbeats compare the boot WIM hash. When a mismatch is detected, the relay downloads the updated WIM automatically.

Once a site holds its WIM it can also serve a Manual Boot ISO - built by the relay while you download it, from that same WIM, and stored nowhere.

Driver Coverage

Every active WinPE driver is embedded in every build, so coverage is a count rather than a comparison: the line above the boot image list shows how many drivers that is and which image is PXE-active. After adding a WinPE driver pack, rebuild the image to pick it up.