Re: [pve-devel] [PATCH corosync] corosync.service: add patch to reduce log spam in broken network setups

[Maximiliano Sandoval <m.sandoval@proxmox.com>]

Friedrich Weber <f.weber@proxmox.com> writes:

> Since c761053 ("Check packets come from the correct interface
> https://github.com/corosync/corosync/issues/750") in kronosnet,
> corosync will produce log messages in certain broken network setups.
> See inner patch for details. Drawing attention to such setups is
> desirable because such setups may experience whole-cluster fences if
> the watchdog is active, see [1].
>
> However, the log volume in such broken setups can be inconveniently
> high. In such a setup, when running the following on node 1:
>
>   # for i in $(seq 100); do dd if=/dev/urandom bs=1M of=/etc/pve/test.bin count=1; done
>
> On node 2, bursts of ~1300 messages per second are observed:
>
>   # journalctl --since="1min ago" -u corosync.service \
>     | cut -d' ' -f 1-3 | uniq -c | sort -n | tail -n 10
>       8 Apr 04 09:51:20
>       8 Apr 04 09:51:24
>       8 Apr 04 09:51:30
>       8 Apr 04 09:51:34
>       8 Apr 04 09:51:40
>      12 Apr 04 09:51:00
>     196 Apr 04 09:51:46
>    1283 Apr 04 09:51:44
>    1329 Apr 04 09:51:43
>    1370 Apr 04 09:51:45
>
> To avoid cluttering the journal, rate-limit log messages to 200 per
> second. See inner patch for details.
>
> [1] https://github.com/corosync/corosync/issues/750
>
> Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
> ---
>
> Notes:
>     I'm a little confused about the rate limit, as with this patch I do
>     see that systemd suppresses messages:
>     
>     Apr 04 09:52:54 coro3 systemd-journald[303]: Suppressed 196 messages from corosync.service
>     
>     but I still see way more than 200 messages per second:
>     
>          11 Apr 04 09:52:00
>          11 Apr 04 09:52:45
>          13 Apr 04 09:52:13
>          14 Apr 04 09:52:12
>          19 Apr 04 09:52:07
>          67 Apr 04 09:52:08
>         400 Apr 04 09:52:54
>         695 Apr 04 09:52:52
>         715 Apr 04 09:52:53
>         835 Apr 04 09:52:51
>     
>     Any idea why?
>
>  ...-rate-limit-log-messages-to-200-per-.patch | 54 +++++++++++++++++++
>  debian/patches/series                         |  1 +
>  2 files changed, 55 insertions(+)
>  create mode 100644 debian/patches/0004-corosync.service-rate-limit-log-messages-to-200-per-.patch
>
> diff --git a/debian/patches/0004-corosync.service-rate-limit-log-messages-to-200-per-.patch b/debian/patches/0004-corosync.service-rate-limit-log-messages-to-200-per-.patch
> new file mode 100644
> index 0000000..0f91b42
> --- /dev/null
> +++ b/debian/patches/0004-corosync.service-rate-limit-log-messages-to-200-per-.patch
> @@ -0,0 +1,54 @@
> +From 5470f01296a3bd8f47fd4bd97939b3a68f00d309 Mon Sep 17 00:00:00 2001
> +From: Friedrich Weber <f.weber@proxmox.com>
> +Date: Fri, 4 Apr 2025 09:14:21 +0200
> +Subject: [PATCH] corosync.service: rate limit log messages to 200 per second
> +
> +Since c761053 ("Check packets come from the correct interface
> +https://github.com/corosync/corosync/issues/750") in kronosnet,
> +corosync will log a message like the following every time a packet is
> +received at the wrong interface, i.e., not the interface on which the
> +corresponding IP is configured:
> +
> +> [KNET  ] udp: Received packet from 10.8.1.1 to 10.8.1.3 on i/f ens20 when expected ens19
> +
> +This is to draw attention to broken network setups that
> +appear to work fine as long as all corosync links are online, but once
> +a link goes down, may go into a state of "asymmetric connectivity"
> +which is problematic for corosync. See [1] for more details.
> +
> +While it is desirable to draw attention to broken setups, the volume
> +of log messages in such clusters can get very high and clutter the
> +journal. In extreme scenarios, occasional bursts of more than 1000
> +messages per second were observed. If we approximate each message with
> +100 bytes, logging 1000 messages per second will produce ~8 GiB of raw
> +logs per day. While this should be a worst case scenario and the
> +logs probably compress well, the volume is still inconveniently high.
> +
> +Hence, use systemd log rate limiting to limit corosync log messages to
> +200 per second, which brings the logs in above scenario down to 1.6
> +GiB/day and should still provide enough headroom to avoid suppressing
> +benign log messages in non-broken setups.
> +
> +[1] https://github.com/corosync/corosync/issues/750
> +
> +Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
> +---
> + init/corosync.service.in | 2 ++

An option that might require lower maintenance would be to ship a
service file override, e.g. at
/lib/systemd/system/corosync.service.d/set-log-rate-limit.conf with
contents:

```
[Service]
LogRateLimitIntervalSec=1s
LogRateLimitBurst=200
```

No strong feelings, it is just a matter of taste.

> + 1 file changed, 2 insertions(+)
> +
> +diff --git a/init/corosync.service.in b/init/corosync.service.in
> +index bd2a48a9..3d7ea2db 100644
> +--- a/init/corosync.service.in
> ++++ b/init/corosync.service.in
> +@@ -10,6 +10,8 @@ EnvironmentFile=-@INITCONFIGDIR@/corosync
> + ExecStart=@SBINDIR@/corosync -f $COROSYNC_OPTIONS
> + ExecStop=@SBINDIR@/corosync-cfgtool -H --force
> + Type=notify
> ++LogRateLimitIntervalSec=1s
> ++LogRateLimitBurst=200

200 hundred messages per second might be a bit too many. Since we are
not sure how many messages a unlucky user might see, I would suggest to
lower it a bit for the time being, 100 is a good round number.

> + 
> + # In typical systemd deployments, both standard outputs are forwarded to
> + # journal (stderr is what's relevant in the pristine corosync configuration),
> +-- 
> +2.39.5
> +
> diff --git a/debian/patches/series b/debian/patches/series
> index 147e793..7a796c4 100644
> --- a/debian/patches/series
> +++ b/debian/patches/series
> @@ -1,3 +1,4 @@
>  0001-Enable-PrivateTmp-in-the-systemd-service-files.patch
>  0002-only-start-corosync.service-if-conf-exists.patch
>  0003-totemsrp-Check-size-of-orf_token-msg.patch
> +0004-corosync.service-rate-limit-log-messages-to-200-per-.patch



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