Incident Report: 20200304
| Incident Report | |
|---|---|
| Dante is hard, mmkay? | |
| Summary | |
| Severity | High |
| Impact | High (Approx 15mins of dead air during a live show, also server reboot) |
| Event Start | 04/03/2020 21:17 |
| Event End | 04/03/2020 21:58 |
| Recurrence Mitigation | See body |
| Contacts | |
| Recovery Leader | Marks Polakovs (MP) |
| Other Attendees | Matthew Stratford (MS), Isaac Lowe (IL), Michael Grace (MG), Jacob Dicker (JD), Jess Schofield (JS) |
Summary
While comp team were investigating CPU load issues on Dolby, the Stores RedNet 3, for seemingly unrelated reasons, drops off the network. This has been seen before. What hasn't been seen before is what happened next: after humming along perfectly happy for 9 minutes, the Dante network started re-electing clock master every 15 seconds, which lead to drop-outs. While trying to fix that, the clock input is switched from BNC to ADAT, which really upsets the Scarlett 18i20, eventually requiring a full reboot of Dolby to get back on air.
What Went Well
- Given the scale of the hardware issues experienced, the fact that we had a total of 15 minutes of dead air is not ideal but could be a lot worse.
- However, a lot of that was off-air-loop, sine-wave, or Flagship News Sosij, which, while technically not dead air, isn't exactly broadcasting. TODO exact numbers, but somewhere around 10m of that.
What Did Not Go So Well
- Took us a while to realise that the RedNet had failed (especially since the error is layer 7 it wouldn't trigger monitoring as that does layer 4)
- Switching clock input to ADAT was a mistake and delayed recovery quite substantially
- Little insight into what happened with the Scarlett, we saw some Jack errors, diagnosed probably hardware/driver error, and made call to reboot system in order to get back on air
- journald is not set to persistent, so the only post-hoc logs we have are from after the reboot
How We Got Lucky
- Almost all current experienced computing team members were in the station and ready to respond quickly
Analysis
A number of related and unrelated issues all happened at the same time:
- Dolby CPU issues - potentially related, potentially not
- Caused by
- Bug in MyRadio causing the sso_session to grow quite a bit with lots of empty sessions
- Bug in Campus Playout putting it into a loop
- Other things?
- Initial dead air - UNKNOWN CAUSE, thonking in progress (probably rednet)
- RedNet 3 failure
- Known hardware/firmware issue, has happened before
- About 9 minutes later, the grandmaster starts cycling - for, as far as we know so far, no good reason
- Scarlett go fucky
- Probably caused by ADAT clock switch and double-clocking
- Caused by human error - mis-understanding of clocking
- Hot coax
- Potential short or other electrical fault in the RedNet or Scarlett
- Full recovery delayed due to issues with SelectorListener
Actions
- MP to remove song that caused Campus Playout bug and high Dolby CPU usage from rotation - Done
- MP to set up emergency back-up audio player on BSOD - Done
- JS and BA to contact Focusrite Support about RedNet issues
- BA to replace clock coax with high-quality SDI cable
- MP to set up Journald persistence on Dolby (and ideally all Debian boxen)
- Purchase alternative Dante<->ADAT interface
- Sort out SelectorListener startup
Timeline
19:00-21:00 MS and MP investigating CPU issues on Dolby.
21:00-21:10 sporadic bits of dead air on AM & online (some presenter error, some potentially Dante related)
21:17:00 MG reports “big issue” in Slack
21:18:35 Dante Controller reports “Device 001DC10208C1 (device name not known) is now a grandmaster” - the RedNet 3 has dropped off
21:18:36 MP screams “DANTE!”
21:19-21:20 MP turns the RedNet 3 off and on again
21:20 Dante starts flapping clock, but seemingly stabilises
21:28 The AM feed becomes noticeably sosig, slowly degrades quality
21:29-21:32 The AM goes to silence with occasional bursts of techno. At the same time, Dante Controller reports various clock switches and devices muting (which is Dante-speak for “oman i am no good with audio pls to halp”). The clock master cycles between Phil, Office, and Studio Red several times. MP says in Slack at 21:31 “[Dante] is not in a good place right now.”
Relevant log entry: 2020-03-04 21:30:53 GMT 1583357453638 Information "uryStores" "Timed out 3 times sending message 'UpdateRxChannels' to uryStores, giving up."
21:33:34 MP, MS, BA set Studio Blue to clock master. Dante sort-of stabilises except not really
21:36:21 IL reports that the clock coax between uryStores and Scarlett is hot to the touch.
Around this time (exact timing TBC) IL attempts switching out the coax, but fails when he realises that the replacement cable is a piece of shit.
21:38:25 we go to DEAD AIR, and at 21:39:14 Dearie-Me triggers.
Around 21:37-39 MP uses RedNet Control to switch the RedNet 3’s clock input to ADAT, believing this will help things, and at 21:38:49 Dante Controller reports that uryStores is clock master. This does not make the Scarlett happy.
21:39:56 Studio Blue is switched to Clock Master, confirmed by MP in Slack at 21:40:07. Still dead air.
21:42 MP tries an audio pipeline restart (aka startAudio.sh). This does not help.
21:44 MP makes the call to reboot Dolby.
21:46:42 Dolby boots to Linux.
21:47:04 MP SSHes into Dolby and tries starting audio, failing.
21:49:41 DEAD AIR ENDS - goes to horrible sosig Flagship News (from the TX OB)
21:50:17 MP runs startAudio.sh
21:50:50 uryStores becomes clock master, at 21:51:09 Dante finishes re-synchronising
21:52:00 horrible sosig Flagship News ends and AM has off-air loop
21:54-21:56 MP realises that SelectorListener isn’t running, and runs some commands to try and start it.
21:58:59 MP declares the incident over