[Bug 1743249] Re: Failed Deployment after timeout trying to retrieve grub cfg

[Andres Rodriguez]

@Jason,

I'm comparing pb in #79 vs pb in #90

#79 (non-patched): https://paste.ubuntu.com/26530737/
#90 (patched with lru_cache): https://paste.ubuntu.com/26531873/

Examples I see in #79:

14:02:ec:42:38:dc # makes 9 requests. on line 160+
14:02:ec:42:28:70 # 8 requests on line 72
14:02:ec:41:d7:38 # 7 on line 92.

In #90 i see:

14:02:ec:41:d7:44 # makes 6 requests on line 7
14:02:ec:42:38:dc # makes 5 requests on line 19


So it is interesting to see that in #79 more machines make more requests than those in #90. Obviously we need more data over time to really tell the difference in both scenarios, but based on the current logs, it does /apparently/ show an improvement.

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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:
  Fix Released

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.

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