In this case your bash scripts and machinery around that is your new
dependency. But you have less contributors and less developers for this
machinary vs taking something more wildly developed and tested from the
community, even if it does the same thing. This is pretty much how it went
with lago. But, at the same time you have full control of it and as soon as
there is a maintainer the path to a fix is quick.
It is the cathedral vs the bazaar kind of question. So, I personally do not
mind either way as soon as there are people maintaining it and we have
clear abstraction boundaries. E.g. if we agree that the end result is
rpm-packaged qcow2 images then I do not want to know how they are produced
as soon as they are. Until the dependent systems start to depend too much
on their specifics there should not be a problem and we are free to modify
and change the builder part.
Over the past five years watching different solutions evolve and die I
think the clear abstraction barriers are what really important rather
than which specific tool is used at each given moment.
On Tue, Apr 28, 2020 at 9:39 AM Michal Skrivanek <
michal.skrivanek(a)redhat.com> wrote:
> On 27 Apr 2020, at 18:37, Nir Soffer <nsoffer(a)redhat.com> wrote:
>
> On Mon, Apr 27, 2020 at 7:21 PM Barak Korren <bkorren(a)redhat.com> wrote:
>>
>>
>>
>> בתאריך יום ב׳, 27 באפר׳ 2020, 17:15, מאת Marcin Sobczyk <
msobczyk(a)redhat.com>:
>>>
>>> Hi,
>>>
>>> recently I've been working on a PoC for OST that replaces the usage
>>> of lago templates with pre-built, layered VM images packed in RPMs
[2][7].
>>>
>>>
>>> What's the motivation?
>>>
>>> There are two big pains around OST - first one is that it's slow
>>> and the second one is it uses lago, which is unmaintained.
>>>
>>>
>>> How is OST working currently?
>>>
>>> Lago launches VMs based on templates. It actually has its own
mechanism for VM
>>> templating - you can find the ones that we currently use here [1]. How
these
>>> templates are created? There is a multiple-page doc somewhere that
describes the process,
>>> but few are familiar with it. These templates are nothing special
really - just a xzipped
>>> qcow with some metadata attached. The proposition here is to replace
those templates with
>>> RPMs with qcows inside. The RPMs themselves would be built by a CI
pipeline. An example
>>> of a pipeline like this can be found here [2].
>>>
>>>
>>> Why RPMs?
>>>
>>> It ticks all the boxes really. RPMs provide:
>>> - tried and well known mechanisms for packaging, versioning, and
distribution instead
>>> of lago's custom ones
>>> - dependencies which permit to layer the VM images in a controllable
way
>>> - we already install RPMs when running OST, so using the new ones is a
matter of adding
>>> some dependencies
>>>
>>>
>>> How the image building pipeline works? [3]
>>>
>>> - we download a dvd iso for installation of the distro
>>> - we use 'virt-install' with the dvd iso + kickstart file to build
a
'base' layer
>>> qcow image
>>> - we create another qcow image that has the 'base' image as the
backing one. In this
>>> image we use 'virt-customize' to run 'dnf upgrade'. This
is our
'upgrade' layer.
>>> - we create two more qcow images that have the 'upgrade' image as
the
backing one. On one
>>> of them we install the 'ovirt-host' package and on the other the
'ovirt-engine'. These are
>>> our 'host-installed' and 'engine-installed' layers.
>>> - we create 4 RPMs for these qcows:
>>> * ost-images-base
>>> * ost-images-upgrade
>>> * ost-images-host-installed
>>> * ost-images-engine-installed
>>> - we publish the RPMs to
templates.ovirt.org/yum/ DNF repository (not
implemented yet)
>>>
>>> Each of those RPMs holds their respective qcow image. They also have
proper dependencies
>>> set up - since 'upgrade' layer requires 'base' layer to be
functional,
it has an RPM
>>> requirement to that package. Same thing happens for '*-installed'
packages which depend on
>>> 'upgrade' package.
>>>
>>> Since this is only a PoC there's still a lot of room for improvement
around the pipeline.
>>> The 'base' RPM would be actually built very rarely, since it's a
bare
distro, and the
>>> 'upgrade' and '*-installed' RPMs would be built nightly.
This would
allow us to simply
>>> type 'dnf upgrade' on any machine and have a fresh set of VMs ready
to
be used with OST.
>>>
>>>
>>> Advantages:
>>>
>>> - we have CI for building OST images instead of current, obscure
template creating process
>>> - we get rid of lots of unnecessary preparations that are done during
each OST run
>>> by moving stuff from 'deploy scripts' [4] to image-building
pipeline
- this should
>>> speed up the runs a lot
>>> - if the nightly pipeline for building images is not successful, the
RPMs won't be
>>> published - OST will use the older ones. This makes a nice "early
error detection"
>>> mechanism and can partially mitigate situations where everything is
blocked because
>>> of some, i.e. dependency issues.
>>> - it's another step for removing responsibilities from lago
>>> - the pre-built VM images can be used for much more than OST -
functional testing of
>>> vdsm/engine on a VM? We have an image for that
>>> - we can build images for multiple distros, both u/s and d/s, easily
>>>
>>>
>>> Caveats:
>>>
>>> - we have to download the RPMs before running OST and that takes time,
since they're big.
>>> This can be handled by having them cached on the CI slaves though.
>>> - current limitations of CI and lago force us to make a copy of the
images after
>>> installation so they can be seen both by the processes in the chroot
and libvirt, which
>>> is running outside of chroot. Right now they're placed in
'/dev/shm'
(which would
>>> actually make some sense if they could be shared among all OST runs
on the slave, but
>>> that's another story). There are some possible workarounds around
that problem too (like
>>> running pipelines on bare metal machines with libvirt running inside
chroot)
>>> - multiple qcow layers can slow down the runs because there's a lot of
jumping around.
>>> This can be handled by i.e. introducing a meta package that squashes
all the layers into
>>> one.
>>> - we need a way to run OST with custom-built artifacts. There are
multiple ways we can
>>> approach it:
>>> * use 'upgrade' layer and not '*-installed' one
>>> * first build your artifacts, then build VM image RPMs that have your
artifacts
>>> installed and pass those RPMs to OST run
>>> * add 'ci build vms' that will do both ^^^ steps for you
>>> Even here we can still benefit from using pre-built images - we can
create
>>> a 'deps-installed' layer that sits between 'upgrade' and
'*-installed' and contains
>>> all vdsm's/engine's dependencies.
>>>
>>>
>>> Some numbers
>>>
>>> So let's take a look at two OST runs - first one that uses the old way
of working [5]
>>> and one that uses the new pre-built VM images [6]. The hacky change
that allows us to
>>> use the pre-built images is here [7]. Here are some running times:
>>>
>>> - chroot init: 00:34 for the old way vs 14:03 for pre-built images
>>>
>>> This happens because the slave didn't have the new RPMs and chroot
cached, so it took a lot
>>> of time to download them - the RPMs are ~2GB currently. When they will
be available
>>> in cache it will get much closer to the old-way timing.
>>>
>>> - deployment times:
>>> * engine 08:09 for the old way vs 03:31 for pre-built images
>>> * host-1 05:05 for the old way vs 02:00 for pre-built images
>>>
>>> Here we can clearly see the benefits. This is without any special fine
tuning really -
>>> even when using pre-built images there's still some deployment done,
which can be moved
>>> to image-creating pipeline.
>>>
>>>
>>> Further improvements
>>>
>>> We could probably get rid of all the funny custom repository stuff
that we're
>>> doing right now because we can put everything that's necessary to
pre-built VM images.
>>>
>>> We can ship the images with ssh key injected - currently lago injects
an ssh
>>> key for root user in each run, which requires selinux relabeling,
which takes a lot
>>> of time.
>>>
>>> We can try creating 'ovirt-deployed' images, where the whole ovirt
solution would
>>> be already deployed for some tests.
>>>
>>> WDYT?
>>
>>
>> We should not reinvent packer.io. It's bad enough we're reinventing
Vagrant with Lago.
>
> Yes, this looks promising:
>
https://www.packer.io/docs/builders/qemu.html
it’s not about reinventing but rather avoiding unnecessary
packages/dependencies
we considered that as well but other than added complexity on top of
virt-install it doesn’t really do anything more.
>
>>> Regards, Marcin
>>>
>>> [1]
https://templates.ovirt.org/repo/
>>> [2]
https://gerrit.ovirt.org/#/c/108430/
>>> [3]
https://gerrit.ovirt.org/#/c/108430/6/ost-images/Makefile.am
>>> [4]
https://github.com/oVirt/ovirt-system-tests/tree/master/common/deploy-scr...
>>> [5]
https://jenkins.ovirt.org/view/oVirt%20system%20tests/job/ovirt-system-te...
>>> [6]
https://jenkins.ovirt.org/job/ovirt-system-tests_standard-check-patch/902...
>>> [7]
https://gerrit.ovirt.org/#/c/108610/
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