Hi folks,
Thank you for additional explanation, it does clarify things a bit. I'd
like to note, however, that you talk a lot about how _different_ Fuel
Agent is from what Ironic does now. I'd like actually to know how well
it's going to fit into what Ironic does (in additional to your specific
use cases). Hence my comments inline:
On 12/09/2014 01:01 PM, Vladimir Kozhukalov wrote:
Just a short explanation of Fuel use case.
Fuel use case is not a cloud. Fuel is a deployment tool. We install OS
on bare metal servers and on VMs
and then configure this OS using Puppet. We have been using Cobbler as
our OS provisioning tool since the beginning of Fuel.
However, Cobbler assumes using native OS installers (Anaconda and
Debian-installer). For some reasons we decided to
switch to image based approach for installing OS.
One of Fuel features is the ability to provide advanced partitioning
schemes (including software RAIDs, LVM).
Native installers are quite difficult to customize in the field of
partitioning
(that was one of the reasons to switch to image based approach).
Moreover, we'd like to implement even more
flexible user experience. We'd like to allow user to choose which hard
drives to use for root FS, for
allocating DB. We'd like user to be able to put root FS over LV or MD
device (including stripe, mirror, multipath).
We'd like user to be able to choose which hard drives are bootable (if
any), which options to use for mounting file systems.
Many many various cases are possible. If you ask why we'd like to
support all those cases, the answer is simple:
because our users want us to support all those cases.
Obviously, many of those cases can not be implemented as image
internals, some cases can not be also implemented on
configuration stage (placing root fs on lvm device).
As far as those use cases were rejected to be implemented in term of
IPA, we implemented so called Fuel Agent.
Important Fuel Agent features are:
* It does not have REST API
I would not call it a feature :-P
Speaking seriously, if you agent is a long-running thing and it gets
it's configuration from e.g. JSON file, how can Ironic notify it of any
changes?
* it has executable entry point[s]
* It uses local json file as it's input
* It is planned to implement ability to download input data via HTTP
(kind of metadata service)
* It is designed to be agnostic to input data format, not only Fuel
format (data drivers)
* It is designed to be agnostic to image format (tar images, file system
images, disk images, currently fs images)
* It is designed to be agnostic to image compression algorithm
(currently gzip)
* It is designed to be agnostic to image downloading protocol (currently
local file and HTTP link)
Does it support Glance? I understand it's HTTP, but it requires
authentication.
So, it is clear that being motivated by Fuel, Fuel Agent is quite
independent and generic. And we are open for
new use cases.
My favorite use case is hardware introspection (aka getting data
required for scheduling from a node automatically). Any ideas on this?
(It's not a priority for this discussion, just curious).
According Fuel itself, our nearest plan is to get rid of Cobbler because
in the case of image based approach it is huge overhead. The question is
which tool we can use instead of Cobbler. We need power management,
we need TFTP management, we need DHCP management. That is
exactly what Ironic is able to do. Frankly, we can implement power/TFTP/DHCP
management tool independently, but as Devananda said, we're all working
on the same problems,
so let's do it together. Power/TFTP/DHCP management is where we are
working on the same problems,
but IPA and Fuel Agent are about different use cases. This case is not
just Fuel, any mature
deployment case require advanced partition/fs management.
Taking into consideration that you're doing a generic OS installation
tool... yeah, it starts to make some sense. For cloud advanced partition
is definitely a "pet" case.
However, for
me it is OK, if it is easily possible
to use Ironic with external drivers (not merged to Ironic and not tested
on Ironic CI).
AFAIU, this spec https://review.openstack.org/#/c/138115/ does not
assume changing Ironic API and core.
Jim asked about how Fuel Agent will know about advanced disk
partitioning scheme if API is not
changed. The answer is simple: Ironic is supposed to send a link to
metadata service (http or local file)
where Fuel Agent can download input json data.
That's not about not changing Ironic. Changing Ironic is ok for
reasonable use cases - we do a huge change right now to accommodate
zapping, hardware introspection and RAID configuration.
I actually have problems with this particular statement. It does not
sound like Fuel Agent will integrate enough with Ironic. This JSON file:
who is going to generate it? In the most popular use case we're driven
by Nova. Will Nova generate this file?
If the answer is "generate it manually for every node", it's too much a
"pet" case for me personally.
As Roman said, we try to be pragmatic and suggest something which does
not break anything. All changes
are supposed to be encapsulated into a driver. No API and core changes.
We have resources to support, test
and improve this driver. This spec is just a zero step. Further steps
are supposed to improve driver
so as to make it closer to Ironic abstractions.
Honestly I think you should at least write a roadmap for it - see my
comments above.
About testing and support: are you providing a 3rdparty CI for it? It
would be a big plus as to me: we already have troubles with drivers
broken accidentally.
For Ironic that means widening use cases and user community. But, as I
already said,
we are OK if Ironic does not need this feature.
I don't think we should through away your hardware provision use case,
but I personally would like to see how well Fuel Agent is going to play
with how Ironic and Nova operate.
Vladimir Kozhukalov
On Tue, Dec 9, 2014 at 1:09 PM, Roman Prykhodchenko
<rprikhodche...@mirantis.com <mailto:rprikhodche...@mirantis.com>> wrote:
It is true that IPA and FuelAgent share a lot of functionality in
common. However there is a major difference between them which is
that they are intended to be used to solve a different problem.
IPA is a solution for provision-use-destroy-use_by_different_user
use-case and is really great for using it for providing BM nodes for
other OS services or in services like Rackspace OnMetal. FuelAgent
itself serves for provision-use-use-…-use use-case like Fuel or
TripleO have.
Those two use-cases require concentration on different details in
first place. For instance for IPA proper decommissioning is more
important than advanced disk management, but for FuelAgent
priorities are opposite because of obvious reasons.
Putting all functionality to a single driver and a single agent may
cause conflicts in priorities and make a lot of mess inside both the
driver and the agent. Actually previously changes to IPA were
blocked right because of this conflict of priorities. Therefore
replacing FuelAgent by IPA in where FuelAgent is used currently does
not seem like a good option because come people (and I’m not talking
about Mirantis) might loose required features because of different
priorities.
Having two separate drivers along with two separate agents for those
different use-cases will allow to have two independent teams that
are concentrated on what’s really important for a specific use-case.
I don’t see any problem in overlapping functionality if it’s used
differently.
P. S.
I realise that people may be also confused by the fact that
FuelAgent is actually called like that and is used only in Fuel atm.
Our point is to make it a simple, powerful and what’s more important
a generic tool for provisioning. It is not bound to Fuel or Mirantis
and if it will cause confusion in the future we will even be happy
to give it a different and less confusing name.
P. P. S.
Some of the points of this integration do not look generic enough or
nice enough. We look pragmatic on the stuff and are trying to
implement what’s possible to implement as the first step. For sure
this is going to have a lot more steps to make it better and more
generic.
On 09 Dec 2014, at 01:46, Jim Rollenhagen <j...@jimrollenhagen.com
<mailto:j...@jimrollenhagen.com>> wrote:
On December 8, 2014 2:23:58 PM PST, Devananda van der Veen
<devananda....@gmail.com <mailto:devananda....@gmail.com>> wrote:
I'd like to raise this topic for a wider discussion outside of the
hallway
track and code reviews, where it has thus far mostly remained.
In previous discussions, my understanding has been that the Fuel team
sought to use Ironic to manage "pets" rather than "cattle" - and
doing
so
required extending the API and the project's functionality in
ways that
no
one else on the core team agreed with. Perhaps that understanding was
wrong
(or perhaps not), but in any case, there is now a proposal to add a
FuelAgent driver to Ironic. The proposal claims this would meet that
teams'
needs without requiring changes to the core of Ironic.
https://review.openstack.org/#/c/138115/
I think it's clear from the review that I share the opinions
expressed in this email.
That said (and hopefully without derailing the thread too much),
I'm curious how this driver could do software RAID or LVM without
modifying Ironic's API or data model. How would the agent know how
these should be built? How would an operator or user tell Ironic
what the disk/partition/volume layout would look like?
And before it's said - no, I don't think vendor passthru API calls
are an appropriate answer here.
// jim
The Problem Description section calls out four things, which have all
been
discussed previously (some are here [0]). I would like to address
each
one,
invite discussion on whether or not these are, in fact, problems
facing
Ironic (not whether they are problems for someone, somewhere),
and then
ask
why these necessitate a new driver be added to the project.
They are, for reference:
1. limited partition support
2. no software RAID support
3. no LVM support
4. no support for hardware that lacks a BMC
#1.
When deploying a partition image (eg, QCOW format), Ironic's PXE
deploy
driver performs only the minimal partitioning necessary to
fulfill its
mission as an OpenStack service: respect the user's request for root,
swap,
and ephemeral partition sizes. When deploying a whole-disk image,
Ironic
does not perform any partitioning -- such is left up to the operator
who
created the disk image.
Support for arbitrarily complex partition layouts is not required by,
nor
does it facilitate, the goal of provisioning physical servers via a
common
cloud API. Additionally, as with #3 below, nothing prevents a
user from
creating more partitions in unallocated disk space once they have
access to
their instance. Therefor, I don't see how Ironic's minimal
support for
partitioning is a problem for the project.
#2.
There is no support for defining a RAID in Ironic today, at all,
whether
software or hardware. Several proposals were floated last cycle;
one is
under review right now for DRAC support [1], and there are multiple
call
outs for RAID building in the state machine mega-spec [2]. Any such
support
for hardware RAID will necessarily be abstract enough to support
multiple
hardware vendor's driver implementations and both in-band
creation (via
IPA) and out-of-band creation (via vendor tools).
Given the above, it may become possible to add software RAID
support to
IPA
in the future, under the same abstraction. This would closely tie the
deploy agent to the images it deploys (the latter image's kernel
would
be
dependent upon a software RAID built by the former), but this would
necessarily be true for the proposed FuelAgent as well.
I don't see this as a compelling reason to add a new driver to the
project.
Instead, we should (plan to) add support for software RAID to the
deploy
agent which is already part of the project.
#3.
LVM volumes can easily be added by a user (after provisioning) within
unallocated disk space for non-root partitions. I have not yet seen a
compelling argument for doing this within the provisioning phase.
#4.
There are already in-tree drivers [3] [4] [5] which do not require a
BMC.
One of these uses SSH to connect and run pre-determined commands.
Like
the
spec proposal, which states at line 122, "Control via SSH access
feature
intended only for experiments in non-production environment," the
current
SSHPowerDriver is only meant for testing environments. We could
probably
extend this driver to do what the FuelAgent spec proposes, as far as
remote
power control for cheap always-on hardware in testing
environments with
a
pre-shared key.
(And if anyone wonders about a use case for Ironic without external
power
control ... I can only think of one situation where I would
rationally
ever
want to have a control-plane agent running inside a
user-instance: I am
both the operator and the only user of the cloud.)
----------------
In summary, as far as I can tell, all of the problem statements upon
which
the FuelAgent proposal are based are solvable through incremental
changes
in existing drivers, or out of scope for the project entirely. As
another
software-based deploy agent, FuelAgent would duplicate the
majority of
the
functionality which ironic-python-agent has today.
Ironic's driver ecosystem benefits from a diversity of
hardware-enablement
drivers. Today, we have two divergent software deployment drivers
which
approach image deployment differently: "agent" drivers use a local
agent to
prepare a system and download the image; "pxe" drivers use a remote
agent
and copy the image over iSCSI. I don't understand how a second driver
which
duplicates the functionality we already have, and shares the same
goals
as
the drivers we already have, is beneficial to the project.
Doing the same thing twice just increases the burden on the team;
we're
all
working on the same problems, so let's do it together.
-Devananda
[0]
https://blueprints.launchpad.net/ironic/+spec/ironic-python-agent-partition
[1] https://review.openstack.org/#/c/107981/
[2]
https://review.openstack.org/#/c/133828/11/specs/kilo/new-ironic-state-machine.rst
[3]
http://git.openstack.org/cgit/openstack/ironic/tree/ironic/drivers/modules/snmp.py
[4]
http://git.openstack.org/cgit/openstack/ironic/tree/ironic/drivers/modules/iboot.py
[5]
http://git.openstack.org/cgit/openstack/ironic/tree/ironic/drivers/modules/ssh.py
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