On Mon, Feb 5, 2018 at 4:07 PM, Andres Rodriguez <andres...@ubuntu-pe.org> wrote: > I think there's a misunderstanding on how the network boot process happens: > Let's look at pxe linux first. Pxe linux does this: > > 1. tries UUID first # if no answer, it moves on > 2. Tries mac # if no answer, it moves on > 3. tries full IP address # if no answer, it moves on > 4. tries partial IP address # if no answer, it moves on > 5. does 4 > 6. does 4 > [...] > 7. boots default. > > This can be seen in here: > > /mybootdir/pxelinux.cfg/b8945908-d6a6-41a9-611d-74a6ab80b83d > /mybootdir/pxelinux.cfg/01-88-99-aa-bb-cc-dd > /mybootdir/pxelinux.cfg/C0A8025B > /mybootdir/pxelinux.cfg/C0A8025 > /mybootdir/pxelinux.cfg/C0A802 > /mybootdir/pxelinux.cfg/C0A80 > /mybootdir/pxelinux.cfg/C0A8 > /mybootdir/pxelinux.cfg/C0A > /mybootdir/pxelinux.cfg/C0 > /mybootdir/pxelinux.cfg/C > /mybootdir/pxelinux.cfg/default > > > That said, in the case of grub, this behavior is similar. You have > described this behavior in comment #16. So what is it that's happening: > > 1. grub is trying grub.cfg-<mac> address multiple times, but since it > doesn't get a response, it gives it. > 2. Once it gives up, grub.cfg-default-amd64 is tried instead. > > That said, the requests are handled completely different. The -<mac> > requests actually accesses the *node* object in the database by searching > it with the mac address where the request is made. With this node object, > we generate the config file. > > In comparison, the -default-amd64 does *not* access the node object. It > just access two config settings and the db query is *much* cheaper. Also, > we have to keep in mind that after grub has done many retries, this returns > rather fast in comparison because it is not only cheaper, but at that point > MAAS may be with way less load of queued DB requests. Either way, grub > giving up means that it wont expect for the initial request, but it will > expect a new response for the new file it asked for. > > That said, this is working *exactly* as expected, because this effectively > tells grub "if config for your MAC address was not returned, you can safely > assume you are an unknown machine to MAAS", hence grub requests a different > config file to start the enlistment process.
Except it's not an unknown machine, and MAAS treating it like one is bad behavior and a bug. This is not "working exactly as expected". "Working exactly as expected" would be my machine being deployed when I asked for it to be. > So this is *not* a race condition in MAAS. This is working as designed and > is expected. The problem here is that MAAS takes too long to answer the > initial request, which causes grub to timeout and move on to request a > different config file. Yes, because there is a race condition in the design - the MAC specific file has to be generated before grub times out. It could instead be generated before the node ever starts booting, allowing it to be served just as fast as the -default-amd64 file is, eliminating that race condition. Jason > On Mon, Feb 5, 2018 at 4:30 PM, Jason Hobbs <jason.ho...@canonical.com> > wrote: > >> The packetdump (comment #35) of MAAS not responding to grub's request >> for the mac specific grub.cfg before grub times out, and then responding >> immediately to the generic-amd64 grub cfg, clearly shows a race >> condition in MAAS. >> >> MAAS's design of dynamically generating the interface specific grub >> config only after it receives the tftp request for it is susceptible to >> a race condition where grub times out before MAAS can respond. >> >> That design is not the only possible design. All the information >> required for the interface specific grub.cfg is available before the >> machine ever powers on, and could be made available on the rack >> controllers at that time too. >> >> Doing so would eliminate that race condition, or at least reduce the >> opportunity greatly, as we see MAAS has no problems immediately >> responding and serving files that it doesn't need to dynamically >> generate at request time. >> >> There is still some question around what in the environment is >> contributing to MAAS not responding faster, and what MAAS is doing while >> it takes 60+ seconds to respond to the request, but that doesn't change >> the fact that the current MAAS design is racy (and that's a bug). >> >> Whatever we change in the environment to reduce the likelihood of >> hitting this issue there doesn't solve the underlying race condition in >> MAAS, and leaves open the possibility of hitting the issue other places >> too. >> >> -- >> You received this bug notification because you are subscribed to MAAS. >> https://bugs.launchpad.net/bugs/1743249 >> >> Title: >> Failed Deployment after timeout trying to retrieve grub cfg >> >> To manage notifications about this bug go to: >> https://bugs.launchpad.net/maas/+bug/1743249/+subscriptions >> >> Launchpad-Notification-Type: bug >> Launchpad-Bug: product=maas; milestone=2.4.x; status=New; >> importance=Undecided; assignee=None; >> Launchpad-Bug: distribution=ubuntu; sourcepackage=grub2; component=main; >> status=In Progress; importance=Medium; assignee=mathieu...@gmail.com; >> Launchpad-Bug-Tags: cdo-qa cdo-qa-blocker foundations-engine patch >> Launchpad-Bug-Information-Type: Public >> Launchpad-Bug-Private: no >> Launchpad-Bug-Security-Vulnerability: no >> Launchpad-Bug-Commenters: andreserl blake-rouse cgregan jason-hobbs vorlon >> Launchpad-Bug-Reporter: Jason Hobbs (jason-hobbs) >> Launchpad-Bug-Modifier: Jason Hobbs (jason-hobbs) >> Launchpad-Message-Rationale: Subscriber (MAAS) >> Launchpad-Message-For: andreserl >> > > > -- > Andres Rodriguez (RoAkSoAx) > Ubuntu Server Developer > MSc. Telecom & Networking > Systems Engineer > > -- > You received this bug notification because you are subscribed to the bug > report. > https://bugs.launchpad.net/bugs/1743249 > > Title: > Failed Deployment after timeout trying to retrieve grub cfg > > Status in MAAS: > New > Status in grub2 package in Ubuntu: > In Progress > > Bug description: > A node failed to deploy after it failed to retrieve a grub.cfg from > MAAS due to a timeout. In the logs, it's clear that the server tried > to retrieve the grub cfg many times, over about 30 seconds: > > http://paste.ubuntu.com/26387256/ > > We see the same thing for other hosts around the same time: > > http://paste.ubuntu.com/26387262/ > > It seems like MAAS is taking way too long to respond to these > requests. > > This is very similar to bug 1724677, which was happening pre- > metldown/spectre. The only difference is we don't see "[critical] TFTP > back-end failed" in the logs anymore. > > I connected to the console on this system and it had errors about > timing out retrieving the grub-cfg, then it had an error message along > the lines of "error not an ip" and then "double free". After I > connected but before I could get a screenshot the system rebooted and > was directed by maas to power off, which it did successfully after > booting to linux. > > Full logs are available here: > https://10.245.162.101/artifacts/14a34b5a-9321-4d1a-b2fa- > ed277a020e7c/cpe_cloud_395/infra-logs.tar > > This is with 2.3.0-6434-gd354690-0ubuntu1~16.04.1. > > To manage notifications about this bug go to: > https://bugs.launchpad.net/maas/+bug/1743249/+subscriptions -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1743249 Title: Failed Deployment after timeout trying to retrieve grub cfg To manage notifications about this bug go to: https://bugs.launchpad.net/maas/+bug/1743249/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
