Possible error in docs regarding log output using supervisor

1

I have been experimenting with running multiple processes in-app and have got it working using supervisord.

I then started looking where to send logs (rather than to local files).

I notice your example conf on Running Multiple Processes Inside A Fly.io App · Fly Docs has …

[supervisord]
logfile=/dev/stdout
...

… however in my experiments, that does not work. It crashes supervisor.

Using /dev/stdout for a process log output works fine. But not for supervisor itself. So it may be worth changing that example to use /dev/null as you say underneath that you don’t want it to generate a log file. Else a file path like /var/log/supervisor.log if you do.

Unless you have got it to work using /dev/stdout. Maybe it’s down to the OS. I’m playing with Alpine linux. And it seems confirmed by others on stackoverflow e.g

2

:thinking: that should not crash. Are there any errors in the logs?

3

Yes, it’s not happy. Even as root. If I switch to using /dev/stdout …

[supervisord]
user=root
nodaemon=true
loglevel=info
;logfile=/dev/null
logfile=/dev/stdout
pidfile=/var/run/supervisord.pid

… the image still builds and deploys, naturally. But when Fly runs the entrypoint (which is supervisor), it crashes:

2022-03-18T20:08:26Z   [info]Preparing to run: `supervisord -c /etc/supervisord.conf` as root
2022-03-18T20:08:26Z   [info]2022/03/18 20:08:26 listening on [fdaa:0:5d9:a7b:23c2:c09d:8057:2]:22 (DNS: [fdaa::3]:53)
2022-03-18T20:08:26Z   [info]2022-03-18 20:08:26,651 INFO Set uid to user 0 succeeded
2022-03-18T20:08:26Z   [info]2022-03-18 20:08:26,651 INFO Set uid to user 0 succeeded
2022-03-18T20:08:26Z   [info]Traceback (most recent call last):
2022-03-18T20:08:26Z   [info]  File "/usr/bin/supervisord", line 33, in <module>
2022-03-18T20:08:26Z   [info]    sys.exit(load_entry_point('supervisor==4.2.2', 'console_scripts', 'supervisord')())
2022-03-18T20:08:26Z   [info]  File "/usr/lib/python3.10/site-packages/supervisor/supervisord.py", line 359, in main
2022-03-18T20:08:26Z   [info]    go(options)
2022-03-18T20:08:26Z   [info]  File "/usr/lib/python3.10/site-packages/supervisor/supervisord.py", line 369, in go
2022-03-18T20:08:26Z   [info]    d.main()
2022-03-18T20:08:26Z   [info]  File "/usr/lib/python3.10/site-packages/supervisor/supervisord.py", line 72, in main
2022-03-18T20:08:26Z   [info]    self.options.make_logger()
2022-03-18T20:08:26Z   [info]  File "/usr/lib/python3.10/site-packages/supervisor/options.py", line 1507, in make_logger
2022-03-18T20:08:26Z   [info]    self.logger.info(msg)
2022-03-18T20:08:26Z   [info]  File "/usr/lib/python3.10/site-packages/supervisor/loggers.py", line 327, in info
2022-03-18T20:08:26Z   [info]  File "/usr/lib/python3.10/site-packages/
2022-03-18T20:08:26Z   [info]  File "/usr/lib/python3.10/site-packages/
upervisor/loggers.py", line 345, in log
2022-03-18T20:08:26Z   [info]    handler.emit(record)
2022-03-18T20:08:26Z   [info]  File "/usr/lib/python3.10/site-packages/supervisor/loggers.py", line 227, in emit
2022-03-18T20:08:26Z   [info]  File "/usr/lib/pyth
2022-03-18T20:08:26Z   [info]  File "/usr/lib/pyth
n3.10/site-packages/supervisor/loggers.py", line 264, in doRollover
2022-03-18T20:08:26Z   [info]    if not (self.stream.tell() >= self.maxBytes):
2022-03-18T20:08:26Z   [info]OSError: [Errno 29] Invalid seek
2022-03-18T20:08:27Z   [info]Main child exited normally with code: 1
2022-03-18T20:08:27Z   [info]Starting clean up.
--> v39 failed - Failed due to unhealthy allocations - rolling back to job version 38 and deploying as v40 

--> Troubleshooting guide at https://fly.io/docs/getting-started/troubleshooting/
Error abort

Seems from that it’s because it’s trying to seek: Invalid seek. So that’s ok with a real file, but not with stdout.

4

Interesting! Check this out: Invalid seek when using logfile = /dev/stdout · Issue #1078 · Supervisor/supervisor · GitHub

1 Like
5

Ah … yes! That’s it. Adding that line then does let it seek and it doesn’t crash.

All good then. Thanks.

1 Like
6

Sounds like we need to update our docs. Can you show us your supervisord config?

7

Ah, well no, the weird thing is I’ve checked your conf in your docs and it does have that line in there :thinking:

Well that’s weird! Maybe I was hacking around with the lines in there (like I’ve just checked the stackoverflow answer also has that logfile_maxbytes=0 and despite that it also says /dev/null) to get it to work. So maybe I removed it.

But with that line and /dev/stdout, it is now working.

My fault it seems.

1 Like