RFC: Disable 'Build' button if host is on and provision method is bootdisk

Bernhard_Suttner · February 12, 2026, 10:52am

Problem Statement

Rebuilding a host is not always possible when the host is powered on, particularly when using the bootdisk provisioning method.

A concrete example is VMware vSphere:

When a VM is running, the bootdisk ISO cannot be attached.
This limitation prevents the rebuild process from completing successfully.

Currently, foreman_bootdisk attempts to work around this by automatically restarting the host during ISO attachment. However:

This restart happens without explicit user warning.
This behavior differs from image-based or network-based provisioning, where no implicit reboot is triggered.
The resulting experience is inconsistent and potentially disruptive.
Sometimes, it still fails because of timing when the “Build” button is pressed.

Proposal

Disable the “Build” button in the UI when:

The host is powered on, and
The selected provisioning method is bootdisk.

This would:

Prevent users from initiating a rebuild that is likely to fail.
Avoid unexpected automatic restarts.
Make the system’s constraints more transparent and predictable.

Motivation

The goal is not to restrict functionality, but to improve usability and consistency. By preventing an invalid or disruptive workflow at the UI level, we can:

Reduce user confusion.
Avoid unintended downtime.

PRs:

github.com/theforeman/foreman

Fixes #39067 - rebuild only if host powered off

develop ← ATIX-AG:rebuild_requires_poweroff

opened 09:41PM - 06 Feb 26 UTC

sbernhard

+26 -8

Rebuild a host is sometimes not possibe if the host is powered on. e.g. there… are 2 issues for bootdisk: 1. on vsphere, if the host is running, the bootdisk can not be attached. To fix this in a user friendly manner, its not possible to fix this only in foreman_bootdisk 2. the current mechanism for vsphere in foreman_bootdisk is, that it restarts the host during attaching the iso image - without a warning that this happens. this isn't user friendly as it is not done for image/network based deployment. Requires https://github.com/theforeman/foreman_bootdisk/pull/180 This is how it currently look like: <img width="406" height="409" alt="image" src="https://github.com/user-attachments/assets/0e93cadf-f584-47a0-832f-b938b762212f" />

Dirk · February 12, 2026, 1:49pm

In the old UI when rebuilding a host on a compute resource a checkbox was shown asking for a reboot. I would personally prefer such a behavior if possible as the user will get a concrete warning when trying to use the functionality and can still use it if wanted by checking the box for the additional action. Otherwise he would need to understand why it is not enabled and in which cases it is possible to do a rebuild which gets even more confusing if in a bigger environment you have different ways of provisioning with different restrictions.

Bernhard_Suttner · February 12, 2026, 2:19pm

This doesn’t solve the issue, unfortunately. Attaching the ISO image often did not work because the request was blocked on vmware.

So, the request to start the “Build” did already fail. Some time ago, a change in foreman_bootdisk tried to solve the issue by stopping the host first and then attach the iso and then start the host again. From UX this would mean, that the host is suddenly gone.

My proposal is, to disable the “Build” button on the Host Details page and add a description that the host needs to be turned off first to set the host in “Build” mode.

Bernhard_Suttner · February 13, 2026, 12:02pm

Just an impression, how it may look like:

This host is running (= powered on) and was provisioned with bootdisk.

Bernhard_Suttner · February 16, 2026, 9:08pm

Other thoughts?

ekohl · February 24, 2026, 10:21am

Like @Dirk said, Foreman has an option to reboot the host when entering build mode:

github.com/theforeman/foreman

app/controllers/hosts_controller.rb

c20ee46e0


      
              end
              format.json do
                render :json => @build.to_json
              end
            end
          end
          
          def setBuild
            forward_url_options
            if @host.setBuild
              if (params[:host] && params[:host][:build] == '1')
                begin
                  if @host.power.reset
                    message = _("Enabled %s for reboot and rebuild")
                  else
                    message = _("Enabled %s for rebuild on next boot, but failed to power cycle the host")
                  end
                  respond_to do |format|
                    format.html do
                      process_success :success_msg => message % @host, :success_redirect => :back
                    end

It may be that the new UI hasn’t ported this over, but it should be possible for the user to show the intent to act now. Though I’m quite sure the orchestration probably never sees this.

IMHO we’re running into limitations of our current orchestration model which is using ActiveRecord hooks instead of proper tasks.

What about the API? I’d like to see the API respond with a clear error first. For example, return HTTP 422 when the above conditions are met and inhibit the whole save.

IIRC the new UI uses the API to perform that action so that should help when the UI is out of sync with the real power status. For example, when the user turned off the VM and someone/something else turned it on without refreshing the Foreman UI page.

That doesn’t block your proposal though it lessens the need for it.

Bernhard_Suttner · February 24, 2026, 8:04pm

Thanks @ekohl for your suggestion.

API-first make sense. I added it to Fixes #39067 - rebuild only if host powered off by sbernhard · Pull Request #10860 · theforeman/foreman · GitHub (including 2 tests)