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

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.

> 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...