osd shutdown may flood the cluster log with 'osd.X reported immediately failed by osd.Y'

[Mauricio Faria de Oliveira]

[Impact]

The `osd_fast_shutdown` option (available in Nautilus and enabled
by default) may cause the cluster log to receive too many entries
of `osd.X reported immediately failed by osd.Y` on large clusters.

This happens as the monitor no longer receives the OSD message to
notify that the OSD is shutting down and now relies on other OSDs
telling it about the failed OSD (not really 'failed' but shutdown.)

This might be an issue for LMA stacks/tools that check ceph logs
for failed lines, and then require additional logic to filter on
an intended OSD (fast) shutdown; might not be an option/possible,
and require an admin to analyze.

[Fix]

The `osd_fast_shutdown_notify_mon` option for OSDs (disabled by
default) can tell the monitor it is shutting down (done in slow/
non-fast shutdown) under `osd_fast_shutdown`.

This introduces minimal delay (the ack from the mon is required
to prevent the messages), and addresses the cluster log issue.
PS: the `osd_mon_shutdown_timeout` option can be used to control
the maximum amount of time waiting for the monitor ack to arrive.

The new option should be available in the following Ceph releases:
- Pacific 16.2.0 [1] [Hirsute+]
- Octopus 15.2.13 [2] [Focal/Groovy; Ussuri+]
- Nautilus 14.2.22) [3] [Eoan is EOL; Train]

This bug tracks the release of this patch in Ubuntu/Cloud Archive.

[Test Case]

- Stop an OSD and watch the OSD and MON logs.

- Before / or with `osd_fast_shutdown_notify_mon = false`:

```
osd log:

2021-01-09T18:59:52.448+0000 7f937fcdc700 -1 received signal: Terminated from -bash (PID: 408) UID: 1000
2021-01-09T18:59:52.448+0000 7f937fcdc700 -1 osd.2 22 *** Got signal Terminated ***
2021-01-09T18:59:52.448+0000 7f937fcdc700 -1 osd.2 22 *** Immediate shutdown (osd_fast_shutdown=true) ***

mon log:

$ cat out/mon.a.log | grep '^2021-01-09T18:59:' | grep 'osd.0 reported immediately failed by osd.' | rev | cut -d: -f1 | rev | sort | uniq -c
      4 osd.0 reported immediately failed by osd.1
      4 osd.0 reported immediately failed by osd.2
      4 osd.0 reported immediately failed by osd.3
      4 osd.0 reported immediately failed by osd.4
      4 osd.0 reported immediately failed by osd.5
      4 osd.0 reported immediately failed by osd.6
      4 osd.0 reported immediately failed by osd.7
      4 osd.0 reported immediately failed by osd.8
      4 osd.0 reported immediately failed by osd.9
```

- After / with `osd_fast_shutdown_notify_mon = true`:

```
osd log:

2021-01-14T17:21:10.825+0000 7feceded1700 -1 received signal: Terminated from -bash (PID: 1750) UID: 1000
2021-01-14T17:21:10.825+0000 7feceded1700 -1 osd.0 80 *** Got signal Terminated ***
2021-01-14T17:21:10.825+0000 7feceded1700 -1 osd.0 80 *** Immediate shutdown (osd_fast_shutdown=true) ***
2021-01-14T17:21:10.825+0000 7feceded1700 0 osd.0 80 prepare_to_stop telling mon we are shutting down
...
2021-01-14T17:21:11.021+0000 7fecdac0c700 0 osd.0 80 got_stop_ack starting shutdown
2021-01-14T17:21:11.021+0000 7feceded1700 0 osd.0 80 prepare_to_stop starting shutdown

mon log:

2021-01-14T17:21:10.829+0000 7f62fce61700 0 log_channel(cluster) log [INF] : osd.0 marked itself down
2021-01-14T17:21:10.885+0000 7f62ff666700 1 mon.a@0(leader).osd e80 do_prune osdmap full prune enabled
2021-01-14T17:21:10.889+0000 7f62ff666700 0 log_channel(cluster) log [WRN] : Health check failed: 1 osds down (OSD_DOWN)
2021-01-14T17:21:10.957+0000 7f62fb65e700 1 mon.a@0(leader).osd e81 e81: 10 total, 9 up, 10 in
2021-01-14T17:21:11.013+0000 7f62fb65e700 0 log_channel(cluster) log [DBG] : osdmap e81: 10 total, 9 up, 10 in
```

[Where problems could occur]

Any regression from this patch should manifest in OSD shutdown, but only when the option is enabled.

The patch is quite small and contained to the OSD shutdown path.

It is effectively a nop when the option is disabled (by default).

It is a small change from the newly introduced default behavior,
but it just re-introduces a message in the shutdown path, which
is how it used to be done on previous releases and even earlier
stable releases in Nautilus.

[1] https://tracker.ceph.com/issues/49683
[2] https://tracker.ceph.com/issues/49681
[3] https://tracker.ceph.com/issues/49682

[Mauricio Faria de Oliveira (mfo)]

Adding target Ubuntu/Cloud Archive releases.

(note: Victoria and Wallaby have no ceph packages yet, thus marking as Invalid.)

```
The new option should be available in the following Ceph releases:
- Pacific 16.2.0 [Hirsute+]
- Octopus 15.2.11 [Focal/Groovy; Ussuri+]
- Nautilus TBD (at least 14.2.20) [Eoan is EOL; Train]

This bug tracks the release of this patch in Ubuntu/Cloud Archive.
```

[Mauricio Faria de Oliveira (mfo)]

New ceph bugfix releases for Nautilus (v14.2.20) and Octopus (v15.2.11) have pushed this another release further.

Also marking Hirsute as Fix Released (v16.2.0+.)

[Mauricio Faria de Oliveira (mfo)]

New ceph hotfix releases for Nautilus (v14.2.21) and Octopus (v15.2.12) have pushed this another release further.

[Mauricio Faria de Oliveira (mfo)]

The option is available on Octopus v15.2.13 [0].
It should not be available in Nautilus anymore, as it's EOL since June 1st, 2021 per [1].

Now waiting on SRU of 15.2.13 in Ubuntu.

[0] https://docs.ceph.com/en/latest/releases/octopus/#v15-2-13-octopus
[1] https://docs.ceph.com/en/latest/releases/

[Mauricio Faria de Oliveira (mfo)]

Groovy is ~1 month to EOL, thus marking it as Invalid.

[Mauricio Faria de Oliveira (mfo)]

Fix already availble in focal & bionic/ussuri.

 ceph | 15.2.14-0ubuntu0.20.04.1 | focal-updates | source

 ceph | 15.2.14-0ubuntu0.20.04.1~cloud0 | ussuri | bionic-updates | source