[ovirt-devel] Re: PoC - using pre-built VM images in OST

On 27 Apr 2020, at 18:37, Nir Soffer <nsoffer(a)redhat.com&gt; wrote: On Mon, Apr 27, 2020 at 7:21 PM Barak Korren <bkorren(a)redhat.com&gt; wrote: > > > > בתאריך יום ב׳, 27 באפר׳ 2020, 17:15, מאת Marcin Sobczyk ‏&lt;msobczyk(a)redhat.com&gt;: >> >> 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

>> 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/ >> _______________________________________________ >> Devel mailing list -- devel(a)ovirt.org >> To unsubscribe send an email to devel-leave(a)ovirt.org >> Privacy Statement: https://www.ovirt.org/privacy-policy.html >> oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ >> List Archives: https://lists.ovirt.org/archives/list/devel@ovirt.org/message/YUXDBHPGQ6E... > > _______________________________________________ > Devel mailing list -- devel(a)ovirt.org > To unsubscribe send an email to devel-leave(a)ovirt.org > Privacy Statement: https://www.ovirt.org/privacy-policy.html > oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ > List Archives: https://lists.ovirt.org/archives/list/devel@ovirt.org/message/EM3HHMSSTUD... _______________________________________________ Devel mailing list -- devel(a)ovirt.org To unsubscribe send an email to devel-leave(a)ovirt.org Privacy Statement: https://www.ovirt.org/privacy-policy.html oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ List Archives: https://lists.ovirt.org/archives/list/devel@ovirt.org/message/KMB35NCSIRE...