Hello All,

This is about adding vendor drivers in Ironic.

In Kilo, we have many vendor drivers getting added in Ironic which is a
very good thing.  But something I noticed is that, most of these reviews
have lots of hardware-specific code in them.  This is something most of the
other Ironic folks cannot understand unless they go and read the hardware
manuals of the vendor hardware about what is being done.  Otherwise we just
need to blindly mark the file as reviewed.

Now let me pitch in with our story about this.  We added a vendor driver
for HP Proliant hardware (the *ilo drivers in Ironic).  Initially we
proposed this same thing in Ironic that we will add all the hardware
specific code in Ironic itself under the directory drivers/modules/ilo.
But few of the Ironic folks didn't agree on this (Devananda especially who
is from my company :)). So we created a new module proliantutils, hosted in
our own github and recently moved it to stackforge.  We gave a limited set
of APIs for Ironic to use - like get_host_power_status(), set_host_power(),
get_one_time_boot(), set_one_time_boot(), etc. (Entire list is here
https://github.com/stackforge/proliantutils/blob/master/proliantutils/ilo/operations.py
).

We have only seen benefits in doing it.  Let me bring in some examples:

1) We tried to add support for some lower version of servers.  We could do
this without making any changes in Ironic (Review in proliantutils
https://review.openstack.org/#/c/153945/)
2) We are adding support for newer models of servers (earlier we use to
talk to servers in protocol called RIBCL, newer servers we will use a
protocol called RIS) - We could do this with just 14 lines of actual code
change in Ironic (this was needed mainly because we didn't think we will
have to use a new protocol itself when we started) -
https://review.openstack.org/#/c/154403/

Now talking about the advantages of putting hardware-specific code in
Ironic:

*1) It's reviewed by Openstack community and tested:*
No. I doubt if I throw in 600 lines of new iLO specific code that is here (
https://github.com/stackforge/proliantutils/blob/master/proliantutils/ilo/ris.py)
for Ironic folks, they will hardly take a look at it.  And regarding
testing, it's not tested in the gate unless we have a 3rd party CI for it.
 [We (iLO drivers) also don't have 3rd party CI right now, but we are
working on it.]

*2) Everything gets packaged into distributions automatically:*
Now the hardware-specific code that we add in Ironic under
drivers/modules/<vendor>/ will get packaged into distributions, but this
code in turn will have dependencies  which needs to be installed manually
by the operator (I assume vendor specific dependencies are not considered
by Linux distributions while packaging Openstack Ironic). Anyone installing
Ironic and wanting to manage my company's servers will again need to
install these dependencies manually.  Why not install the wrapper if there
is one too.

I assume we only get these advantages by moving all of hardware-specific
code to a wrapper module in stackforge and just exposing some APIs for
Ironic to use:
* Ironic code would be much cleaner and easier to maintain
* Any changes related to your hardware - support for newer hardware, bug
fixes in particular models of hardware, would be very easy. You don't need
to change Ironic code for that. You could just fix the bug in your module,
release a new version and ask your users to install a newer version of the
module.
* python-fooclient could be used outside Ironic to easily manage foo
servers.
* Openstack CI for free if you are in stackforge - unit tests, flake tests,
doc generation, merge, pypi release everything handled automatically.

I don't see any disadvantages.

Now regarding the time taken to do this, if you have all the code ready now
in Ironic (which assume you will already have), perhaps it will take a day
to do this - half a day for putting into a separate module in python/github
and half a day for stackforge. The request to add stackforge should get
approved in the same day (if everything is all-right).

Let me know all of your thoughts on this.  If we agree, I feel we should
have some documentation on it in our Ironic docs directory.

Thanks for reading :)

Regards,
Ramesh
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