I would like to begin defining and documenting the API for the backend code as
people are actively working on developing new modules. I have begun some pages
on the Confluence site and would like to start discussing this.
API development is somewhat related to the image capture and modularization
issues discussed at the meeting on 2/5. Solving the issues requires the
modularization architecture to be modified and the API should be
specified/updated along the way.
The main problem is that xCAT.pm expects the OS to reboot when the OS capture
tasks are done and vmware.pm needs the OS to shut down. xCAT.pm is currently
the only provisioning module which has had the OS-specific code removed and is
fully modularized. vmware.pm still contains OS code. It will be difficult to
modularize vmware.pm and the ESX.pm module that Brian and Andrew are working on
because of this.
I have given it some thought and would like to propose the numbered changes
below. These changes probably sound bigger than they really are. Minor changes
would need to be made to xCAT.pm and image.pm. This will be easier to
understand if you look at the diagram on the following page:
http://cwiki.apache.org/confluence/display/VCL/Image+Capture+Sequence
1. The name of the OS module's capture_prepare subroutine will be changed to
pre_capture(). The reason for this is to align the name of the main OS capture
subroutine with the main OS load subroutine - pre_capture() and post_load().
2. image.pm will no longer call the OS::pre_capture() subroutine. It will be
the provisioning module's responsibility to do this. This allows the
provisioning module to have greater control over the capture sequence. image.pm
will only call the provisioning module's capture() subroutine. This makes
better sense to me because provisioning engines can be quite varied and the
sequence should really be driven by the provisioning module.
3. OS::pre_capture() will accept an optional argument named 'end_state' with
possible values 'on', 'off', 'reboot'. This instructs OS::pre_capture() what to
do after completing its image capture steps. Because pre_capture() will be
called by the provisioning module, the provisioning module will be able to have
the computer left in the state it requires. The default value will be off,
meaning the OS will shut the computer down after its pre_capture() tasks are done.
4. OS::capture_start() will be eliminated. All OS capture steps will be handled
by a single subroutine - pre_capture() including the final steps of calling
sysprep.exe if Windows and leaving the computer in the state described in #3. I
don't see a need to separate pre_capture() and capture_start().
5. Provisioning::capture_monitor() will be eliminated. Control is passed from
image.pm to the provisioning module's capture() subroutine. If capture() needs
to monitor the image being saved, it can either do so directly in capture() or
call another subroutine within the provisioning module.
There are some other pages I started on the Confluence site. They are somewhat
messy at the moment. Feel free to add to them:
General documentation for modularization:
http://cwiki.apache.org/confluence/display/VCL/Modularized+Architecture
OS module API specification:
http://cwiki.apache.org/confluence/display/VCL/Operating+System+Module+Interface+Specification
Provisioning module API specification:
http://cwiki.apache.org/confluence/display/VCL/Provisioning+Engine+Module+Interface+Specification
Thanks,
Andy
