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Apache with CGI intermittently unresponsive

Hello everybody,

I'm running Apache 2.4.18 as part of a publicly accessible database on a dedicated server,
i.e. it is mostly serving content by CGI and has some static webpages.

I had over the last two years the problem that the server every now and then stopped
to respond to any requests for an hour or so and then resumed to normal, without any
intervention. Now since the last two days the problem happens several times a day.
How can I avoid these hiccups, or at least: where can I find more information to figure
out the cause?

I have root permissions on the server and the developer of the executed database service,
thus I'm happy to run any diagnostics that may help. Looking into Apache's error log did
not show any relevant entries at all.

I can login during the no-response events by SSH on port 25. The commands top and iotop
show that the server is idling, i.e. almost no load on CPU, disk, or RAM. The backend
database is a mirror, i.e. it keeps synchronized with a upstream remote database, and
that works too during the hiccups, i.e. outbound HTTPS works, and the server itself works
as well.

I have setup a watchdog to restart Apache when it is unable to fetch a static page from
the localhost; it is called per cronjob once per minute:

#!/usr/bin/env bash

START_DATE="$(date '+%T')"
LOCK_FILE=/root/bin/restart_apache.lock
TEMP=$(mktemp)
wget --timeout=2 -nv -O $TEMP "http://localhost"
if [[ -s $TEMP ]]; then
echo "$(date '+%T'): all ok"
rm -f $LOCK_FILE
elif [[ -s $LOCK_FILE ]]; then
echo "$(date '+%T'): No response from Apache, restart already pending"
ps -ef | grep -E 'apache|wget'
else
echo "$(date '+%T'): No response from Apache, restarting"
ps -ef | grep -E 'apache|wget'
echo "$START_DATE" >$LOCK_FILE
apache2ctl restart
fi
rm -fR $TEMP

and the result is:

19:40:01: all ok
19:41:01: all ok
19:42:01: all ok
19:43:01: all ok
19:44:01: all ok
19:45:01: all ok
19:46:01: all ok
19:47:01: all ok
19:48:01: all ok
19:52:06: No response from Apache, restarting
root 1213 1 0 Oct04 ? 00:00:13 /usr/sbin/apache2 -k start
www-data 1216 1213 0 19:21 ? 00:00:16 /usr/sbin/apache2 -k start
root 1523 1521 0 19:49 ? 00:00:00 /bin/sh -c /root/bin/restart_apache.sh 2>&1 >>/root/bin/restart_apache.log
root 1525 1523 0 19:49 ? 00:00:00 bash /root/bin/restart_apache.sh
root 4666 4660 0 19:50 ? 00:00:00 /bin/sh -c /root/bin/restart_apache.sh 2>&1 >>/root/bin/restart_apache.log
root 4668 4666 0 19:50 ? 00:00:00 bash /root/bin/restart_apache.sh
root 4673 4668 0 19:50 ? 00:00:00 wget --timeout=2 -nv -O /tmp/tmp.TYXwpFWKsv <a href="http://localhost" title="http://localhost">http://localhost</a>
www-data 6506 1213 1 18:44 ? 00:00:49 /usr/sbin/apache2 -k start
root 8176 8174 0 19:51 ? 00:00:00 /bin/sh -c /root/bin/restart_apache.sh 2>&1 >>/root/bin/restart_apache.log
root 8178 8176 0 19:51 ? 00:00:00 bash /root/bin/restart_apache.sh
root 8187 8178 0 19:51 ? 00:00:00 wget --timeout=2 -nv -O /tmp/tmp.tRbLDKRb3N <a href="http://localhost" title="http://localhost">http://localhost</a>
www-data 10490 1213 0 19:24 ? 00:00:01 /usr/sbin/apache2 -k start
root 11195 11193 0 19:52 ? 00:00:00 /bin/sh -c /root/bin/restart_apache.sh 2>&1 >>/root/bin/restart_apache.log
root 11196 11195 0 19:52 ? 00:00:00 bash /root/bin/restart_apache.sh
root 11200 11196 0 19:52 ? 00:00:00 wget --timeout=2 -nv -O /tmp/tmp.OzlILk3qYF <a href="http://localhost" title="http://localhost">http://localhost</a>
root 11477 1525 0 19:52 ? 00:00:00 grep -E apache|wget
www-data 12228 1213 0 19:15 ? 00:00:16 /usr/sbin/apache2 -k start
www-data 13391 1213 1 18:37 ? 00:00:47 /usr/sbin/apache2 -k start
www-data 15160 1213 2 19:33 ? 00:00:24 /usr/sbin/apache2 -k start
root 16780 16685 0 19:43 pts/0 00:00:00 less bin/restart_apache.log
www-data 18921 1213 1 19:17 ? 00:00:40 /usr/sbin/apache2 -k start
www-data 20378 1213 1 18:13 ? 00:01:23 /usr/sbin/apache2 -k start
www-data 25668 1213 1 16:31 ? 00:02:53 /usr/sbin/apache2 -k start
www-data 28476 1213 1 11:05 ? 00:09:04 /usr/sbin/apache2 -k start
www-data 31152 1213 0 19:38 ? 00:00:02 /usr/sbin/apache2 -k start
www-data 31358 1213 1 19:20 ? 00:00:25 /usr/sbin/apache2 -k start
19:53:06: No response from Apache, restart already pending
root 1213 1 0 Oct04 ? 00:00:13 /usr/sbin/apache2 -k start
www-data 1216 1213 0 19:21 ? 00:00:16 /usr/sbin/apache2 -k start
root 4666 4660 0 19:50 ? 00:00:00 /bin/sh -c /root/bin/restart_apache.sh 2>&1 >>/root/bin/restart_apache.log
root 4668 4666 0 19:50 ? 00:00:00 bash /root/bin/restart_apache.sh
www-data 6506 1213 1 18:44 ? 00:00:49 /usr/sbin/apache2 -k start
root 8176 8174 0 19:51 ? 00:00:00 /bin/sh -c /root/bin/restart_apache.sh 2>&1 >>/root/bin/restart_apache.log
root 8178 8176 0 19:51 ? 00:00:00 bash /root/bin/restart_apache.sh
root 8187 8178 0 19:51 ? 00:00:00 wget --timeout=2 -nv -O /tmp/tmp.tRbLDKRb3N <a href="http://localhost" title="http://localhost">http://localhost</a>
www-data 10490 1213 0 19:24 ? 00:00:01 /usr/sbin/apache2 -k start
root 11195 11193 0 19:52 ? 00:00:00 /bin/sh -c /root/bin/restart_apache.sh 2>&1 >>/root/bin/restart_apache.log
root 11196 11195 0 19:52 ? 00:00:00 bash /root/bin/restart_apache.sh
root 11200 11196 0 19:52 ? 00:00:00 wget --timeout=2 -nv -O /tmp/tmp.OzlILk3qYF <a href="http://localhost" title="http://localhost">http://localhost</a>
www-data 12228 1213 0 19:15 ? 00:00:16 /usr/sbin/apache2 -k start
www-data 13391 1213 1 18:37 ? 00:00:47 /usr/sbin/apache2 -k start
root 14621 14618 0 19:53 ? 00:00:00 /bin/sh -c /root/bin/restart_apache.sh 2>&1 >>/root/bin/restart_apache.log
root 14622 14621 0 19:53 ? 00:00:00 bash /root/bin/restart_apache.sh
root 14631 14622 0 19:53 ? 00:00:00 wget --timeout=2 -nv -O /tmp/tmp.ak1ncMEZTk <a href="http://localhost" title="http://localhost">http://localhost</a>
root 14928 4668 0 19:53 ? 00:00:00 grep -E apache|wget
www-data 15160 1213 2 19:33 ? 00:00:25 /usr/sbin/apache2 -k start
root 16780 16685 0 19:43 pts/0 00:00:00 less bin/restart_apache.log
www-data 18921 1213 1 19:17 ? 00:00:41 /usr/sbin/apache2 -k start
www-data 20378 1213 1 18:13 ? 00:01:24 /usr/sbin/apache2 -k start
www-data 25668 1213 1 16:31 ? 00:02:53 /usr/sbin/apache2 -k start
www-data 28476 1213 1 11:05 ? 00:09:05 /usr/sbin/apache2 -k start
www-data 31152 1213 0 19:38 ? 00:00:02 /usr/sbin/apache2 -k start
www-data 31358 1213 1 19:20 ? 00:00:25 /usr/sbin/apache2 -k start
19:53:10: all ok
19:53:18: all ok
19:53:18: all ok
19:54:01: all ok
19:55:01: all ok
19:56:01: all ok
19:57:01: all ok
19:58:01: all ok
19:59:01: all ok
20:00:01: all ok

i.e. Apache is really not serving any page, not even a static one, and not even via localhost. Both ports 80 and 443 are affected.
I'm confused that whatever is happening is able to keep wget as the client blocked as well despite the timeout.

The network is up and working (inbound SSH and outbound HTTP are productively used).

The backend services are up and running (the database can be queried locally and continues to perform updates from upstream).

I'm now logging error with level

LogLevel debug ssl:warn deflate:warn authz_core:warn

and I get

[Tue Oct 08 19:41:39.958773 2019] [reqtimeout:info] [pid 20378:tid 140538669868800] [client 2600:1004:b16e:33ee:edf5:39df:eedb:2415:55780] AH01382: Request header read timeout
[Tue Oct 08 19:42:17.590793 2019] [reqtimeout:info] [pid 20378:tid 140538787366656] [client 2.205.184.188:58061] AH01382: Request header read timeout
[Tue Oct 08 19:42:51.922775 2019] [reqtimeout:info] [pid 15160:tid 140538804152064] [client 2003:c7:270e:300:f7c4:e25c:38e5:b67b:36756] AH01382: Request header read timeout
[Tue Oct 08 19:43:35.378772 2019] [reqtimeout:info] [pid 20378:tid 140538804152064] [client 75.146.44.253:53241] AH01382: Request header read timeout
[Tue Oct 08 19:44:05.630783 2019] [reqtimeout:info] [pid 15160:tid 140538846115584] [client 173.62.82.134:54143] AH01382: Request header read timeout
[Tue Oct 08 19:44:06.194973 2019] [core:info] [pid 15160:tid 140538745403136] [client 196.229.217.165:60880] AH00128: File does not exist: /var/www/favicon.ico, referer: <a href="https://overpass-api.de/api/convert" title="https://overpass-api.de/api/convert">https://overpass-api.de/api/convert</a>
[Tue Oct 08 19:44:31.221836 2019] [core:info] [pid 15160:tid 140538820937472] [client 80.131.127.90:57848] AH00128: File does not exist: /var/www/favicon.ico
[Tue Oct 08 19:45:06.168750 2019] [core:info] [pid 12228:tid 140538695046912] [client 80.131.127.90:57877] AH00128: File does not exist: /var/www/favicon.ico
[Tue Oct 08 19:45:38.528606 2019] [core:info] [pid 15160:tid 140538745403136] [client 80.131.127.90:57896] AH00128: File does not exist: /var/www/favicon.ico
[Tue Oct 08 19:46:00.518764 2019] [reqtimeout:info] [pid 15160:tid 140538728617728] [client 196.229.217.165:60895] AH01382: Request header read timeout
[Tue Oct 08 19:46:11.900794 2019] [reqtimeout:info] [pid 20378:tid 140538644690688] [client 45.4.216.53:50224] AH01382: Request header read timeout
[Tue Oct 08 19:46:32.750177 2019] [mpm_event:debug] [pid 20378:tid 140538737010432] event.c(1123): (104)Connection reset by peer: [client 82.132.239.56:35811] AH00470: network write failure in core output filter
[Tue Oct 08 19:47:05.970785 2019] [reqtimeout:info] [pid 13391:tid 140538787366656] [client 158.106.118.12:53203] AH01382: Request header read timeout
[Tue Oct 08 19:47:47.178782 2019] [reqtimeout:info] [pid 18921:tid 140538653083392] [client 173.62.82.134:54168] AH01382: Request header read timeout
[Tue Oct 08 19:47:53.372715 2019] [mpm_event:debug] [pid 28476:tid 140538770581248] event.c(1123): (104)Connection reset by peer: [client 2607:fb90:17d1:645c:4c90:5573:7466:6982:49928] AH00470: network write failure in core output filter
[Tue Oct 08 19:47:57.704105 2019] [mpm_event:debug] [pid 18921:tid 140538669868800] event.c(1123): (104)Connection reset by peer: [client 2607:fb90:17d1:645c:4c90:5573:7466:6982:49929] AH00470: network write failure in core output filter
[Tue Oct 08 19:48:02.472628 2019] [mpm_event:debug] [pid 20378:tid 140538820937472] event.c(1123): (104)Connection reset by peer: [client 2607:fb90:17d1:645c:4c90:5573:7466:6982:49930] AH00470: network write failure in core output filter
[Tue Oct 08 19:48:32.548604 2019] [mpm_event:debug] [pid 25668:tid 140538737010432] event.c(1123): (32)Broken pipe: [client 81.19.92.168:2342] AH00470: network write failure in core output filter
[Tue Oct 08 19:48:58.631533 2019] [mpm_event:debug] [pid 25668:tid 140538795759360] event.c(1123): (104)Connection reset by peer: [client 174.255.7.174:7655] AH00470: network write failure in core output filter
[Tue Oct 08 19:49:04.139602 2019] [mpm_event:debug] [pid 20378:tid 140538737010432] event.c(1123): (32)Broken pipe: [client 81.19.92.170:5344] AH00470: network write failure in core output filter
[Tue Oct 08 19:49:04.551057 2019] [mpm_event:debug] [pid 20378:tid 140538770581248] event.c(1123): (32)Broken pipe: [client 81.19.92.171:5686] AH00470: network write failure in core output filter
[Tue Oct 08 19:49:06.143003 2019] [mpm_event:debug] [pid 20378:tid 140538644690688] event.c(1123): (104)Connection reset by peer: [client 2600:387:5:802::63:23802] AH00470: network write failure in core output filter
[Tue Oct 08 19:49:27.396581 2019] [mpm_event:debug] [pid 25668:tid 140538804152064] event.c(1123): (104)Connection reset by peer: [client 2600:1700:ce60:10c0:6d01:4b51:312f:c9d:50693] AH00470: network write failure in core output filter
[Tue Oct 08 19:49:41.444772 2019] [mpm_event:debug] [pid 6506:tid 140538770581248] event.c(1123): (104)Connection reset by peer: [client 2600:1:b30e:289c:4171:88c5:37d0:4b3f:61129] AH00470: network write failure in core output filter
[Tue Oct 08 19:49:44.596890 2019] [mpm_event:debug] [pid 13391:tid 140538678261504] event.c(1123): (104)Connection reset by peer: [client 107.72.178.81:9186] AH00470: network write failure in core output filter
[Tue Oct 08 19:49:51.377113 2019] [mpm_event:debug] [pid 18921:tid 140538795759360] event.c(1123): (104)Connection reset by peer: [client 31.4.226.154:41180] AH00470: network write failure in core output filter
[Tue Oct 08 19:50:04.884051 2019] [mpm_event:debug] [pid 15160:tid 140538686654208] event.c(1123): (104)Connection reset by peer: [client 2600:387:9:5::8a:31659] AH00470: network write failure in core output filter
[Tue Oct 08 19:50:33.845588 2019] [mpm_event:debug] [pid 12228:tid 140538753795840] event.c(1123): (32)Broken pipe: [client 81.19.92.168:14784] AH00470: network write failure in core output filter
[Tue Oct 08 19:51:07.906793 2019] [reqtimeout:info] [pid 20378:tid 140538812544768] [client 196.229.217.165:60911] AH01382: Request header read timeout
[Tue Oct 08 19:51:09.587342 2019] [reqtimeout:info] [pid 28476:tid 140538711832320] [client 107.77.203.190:22323] AH01382: Request header read timeout
[Tue Oct 08 19:51:28.104114 2019] [mpm_event:debug] [pid 20378:tid 140538846115584] event.c(1123): (32)Broken pipe: [client 200.32.120.219:54968] AH00470: network write failure in core output filter
[Tue Oct 08 19:51:42.330885 2019] [cgi:error] [pid 15160:tid 140538745403136] [client 78.220.13.56:38905] AH02811: script not found or unable to stat: /usr/lib/cgi-bin/ViewLog.asp
[Tue Oct 08 19:51:46.870776 2019] [reqtimeout:info] [pid 6506:tid 140538837722880] [client 2a02:c7d:8e93:cb00:d103:48fb:1fbe:f9ba:51228] AH01382: Request header read timeout
[Tue Oct 08 19:51:48.807704 2019] [mpm_event:debug] [pid 18921:tid 140538737010432] event.c(1123): (104)Connection reset by peer: [client 75.118.59.50:62595] AH00470: network write failure in core output filter
[Tue Oct 08 19:51:50.391271 2019] [mpm_event:debug] [pid 25668:tid 140538770581248] event.c(1123): (104)Connection reset by peer: [client 75.118.59.50:62601] AH00470: network write failure in core output filter
[Tue Oct 08 19:51:53.631047 2019] [cgi:error] [pid 13391:tid 140538770581248] [client 89.155.38.229:5242] AH01215: /opt/128k_osm3s/cgi-bin/interpreter: line 18: 8967 Done echo "$REQUEST": /opt/128k_osm3s/cgi-bin/interpreter, referer: <a href="https://overpass-turbo.eu/" title="https://overpass-turbo.eu/">https://overpass-turbo.eu/</a>
[Tue Oct 08 19:51:53.631100 2019] [cgi:error] [pid 13391:tid 140538770581248] [client 89.155.38.229:5242] AH01215: 8968 Killed | ./interpreter_bin: /opt/128k_osm3s/cgi-bin/interpreter, referer: <a href="https://overpass-turbo.eu/" title="https://overpass-turbo.eu/">https://overpass-turbo.eu/</a>
[Tue Oct 08 19:51:53.631113 2019] [cgi:error] [pid 13391:tid 140538770581248] [client 89.155.38.229:5242] End of script output before headers: interpreter, referer: <a href="https://overpass-turbo.eu/" title="https://overpass-turbo.eu/">https://overpass-turbo.eu/</a>
[Tue Oct 08 19:51:53.631629 2019] [cgi:error] [pid 12228:tid 140538762188544] [client 89.155.38.229:5250] AH01215: /opt/128k_osm3s/cgi-bin/kill_my_queries: line 43: kill: (8968) - No such process: /opt/128k_osm3s/cgi-bin/kill_my_queries, referer: <a href="https://overpass-turbo.eu/" title="https://overpass-turbo.eu/">https://overpass-turbo.eu/</a>
[Tue Oct 08 19:52:05.688009 2019] [reqtimeout:info] [pid 12228:tid 140538653083392] [client 86.155.20.233:48710] AH01382: Request header read timeout
[Tue Oct 08 19:52:20.854771 2019] [reqtimeout:info] [pid 28476:tid 140538837722880] [client 2a02:c7d:9b70:df00:1837:e9f4:21b9:f6e0:51230] AH01382: Request header read timeout
[Tue Oct 08 19:52:23.419712 2019] [mpm_event:debug] [pid 18921:tid 140538653083392] event.c(1123): (104)Connection reset by peer: [client 2600:387:2:804::33:16047] AH00470: network write failure in core output filter
[Tue Oct 08 19:52:39.358102 2019] [mpm_event:debug] [pid 25668:tid 140538804152064] event.c(1123): (32)Broken pipe: [client 81.19.92.170:27899] AH00470: network write failure in core output filter
[Tue Oct 08 19:52:50.675555 2019] [mpm_event:debug] [pid 6506:tid 140538737010432] event.c(1123): (32)Broken pipe: [client 2a02:c7f:763c:2200:50cf:4d34:2a71:eed6:59668] AH00470: network write failure in core output filter
[Tue Oct 08 19:53:01.759878 2019] [mpm_event:debug] [pid 28476:tid 140538804152064] event.c(1123): (104)Connection reset by peer: [client 2a02:c7f:763c:2200:50cf:4d34:2a71:eed6:59669] AH00470: network write failure in core output filter
[Tue Oct 08 19:53:18.386778 2019] [reqtimeout:info] [pid 6506:tid 140538762188544] [client 94.197.121.47:25307] AH01382: Request header read timeout
[Tue Oct 08 19:53:30.652849 2019] [mpm_event:debug] [pid 28476:tid 140538804152064] event.c(1123): (104)Connection reset by peer: [client 99.203.24.76:33578] AH00470: network write failure in core output filter
[Tue Oct 08 19:53:36.589687 2019] [core:info] [pid 13391:tid 140538753795840] [client 188.148.246.187:49409] AH00128: File does not exist: /var/www/favicon.ico, referer: <a href="http://www.overpass-api.de/public_transport.html" title="http://www.overpass-api.de/public_transport.html">http://www.overpass-api.de/public_transport.html</a>
[Tue Oct 08 19:54:32.555797 2019] [core:info] [pid 20378:tid 140538804152064] [client 8.20.51.223:8052] AH00128: File does not exist: /var/www/favicon.ico, referer: <a href="https://overpass-api.de/api/map?bbox=-275.6,-79.8,86.5,83.1" title="https://overpass-api.de/api/map?bbox=-275.6,-79.8,86.5,83.1">https://overpass-api.de/api/map?bbox=-275.6,-79.8,86.5,83.1</a>
[Tue Oct 08 19:55:01.461985 2019] [mpm_event:debug] [pid 12228:tid 140538753795840] event.c(1123): (104)Connection reset by peer: [client 178.197.228.79:9042] AH00470: network write failure in core output filter
[Tue Oct 08 19:55:15.094770 2019] [reqtimeout:info] [pid 6506:tid 140538829330176] [client 41.176.251.166:58813] AH01382: Request header read timeout
[Tue Oct 08 19:55:15.478810 2019] [reqtimeout:info] [pid 12228:tid 140538787366656] [client 41.176.251.166:58810] AH01382: Request header read timeout
[Tue Oct 08 19:55:31.517919 2019] [mpm_event:debug] [pid 18921:tid 140538762188544] event.c(1123): (32)Broken pipe: [client 111.225.148.25:53638] AH00470: network write failure in core output filter
[Tue Oct 08 19:55:58.028131 2019] [mpm_event:debug] [pid 6506:tid 140538778973952] event.c(1123): (104)Connection reset by peer: [client 2600:387:5:802::63:25658] AH00470: network write failure in core output filter
[Tue Oct 08 19:56:05.834773 2019] [reqtimeout:info] [pid 20378:tid 140538745403136] [client 143.167.254.166:59307] AH01382: Request header read timeout
[Tue Oct 08 19:56:16.558155 2019] [mpm_event:debug] [pid 6506:tid 140538829330176] event.c(1123): (104)Connection reset by peer: [client 166.182.82.205:55282] AH00470: network write failure in core output filter
[Tue Oct 08 19:56:21.602301 2019] [mpm_event:debug] [pid 15160:tid 140538778973952] event.c(1123): (104)Connection reset by peer: [client 166.182.82.205:55283] AH00470: network write failure in core output filter
[Tue Oct 08 19:56:57.344369 2019] [mpm_event:debug] [pid 25668:tid 140538753795840] event.c(1123): (104)Connection reset by peer: [client 188.140.144.123:8080] AH00470: network write failure in core output filter
[Tue Oct 08 19:56:59.451537 2019] [mpm_event:debug] [pid 12228:tid 140538820937472] event.c(1123): (104)Connection reset by peer: [client 188.140.144.123:8488] AH00470: network write failure in core output filter
[Tue Oct 08 19:57:02.878156 2019] [mpm_event:debug] [pid 6506:tid 140538703439616] event.c(1123): (104)Connection reset by peer: [client 188.140.144.123:7926] AH00470: network write failure in core output filter
[Tue Oct 08 19:57:07.591984 2019] [mpm_event:debug] [pid 12228:tid 140538745403136] event.c(1123): (104)Connection reset by peer: [client 2a02:a448:77dd:1:b018:aa19:82e6:4ff5:51061] AH00470: network write failure in core output filter
[Tue Oct 08 19:57:38.661691 2019] [reqtimeout:info] [pid 12228:tid 140538653083392] [client 63.143.132.62:60468] AH01382: Request header read timeout
[Tue Oct 08 19:57:43.386803 2019] [reqtimeout:info] [pid 28476:tid 140538653083392] [client 41.141.119.171:59888] AH01382: Request header read timeout
[Tue Oct 08 19:57:45.194773 2019] [reqtimeout:info] [pid 6506:tid 140538795759360] [client 2003:c7:270e:300:f7c4:e25c:38e5:b67b:36890] AH01382: Request header read timeout
[Tue Oct 08 19:58:04.350948 2019] [core:info] [pid 12228:tid 140538846115584] [client 91.114.215.27:49631] AH00128: File does not exist: /var/www/apple-touch-icon-precomposed.png
[Tue Oct 08 19:58:04.562940 2019] [core:info] [pid 25668:tid 140538720225024] [client 91.114.215.27:49633] AH00128: File does not exist: /var/www/apple-touch-icon.png
[Tue Oct 08 19:58:09.670780 2019] [reqtimeout:info] [pid 6506:tid 140538644690688] [client 2a02:c7d:de57:4500:4dd:7bb0:c147:b2ee:51114] AH01382: Request header read timeout
[Tue Oct 08 19:58:09.678774 2019] [reqtimeout:info] [pid 6506:tid 140538737010432] [client 2a02:c7d:de57:4500:4dd:7bb0:c147:b2ee:51115] AH01382: Request header read timeout
[Tue Oct 08 19:58:09.682773 2019] [reqtimeout:info] [pid 6506:tid 140538829330176] [client 2a02:c7d:de57:4500:4dd:7bb0:c147:b2ee:51116] AH01382: Request header read timeout
[Tue Oct 08 19:58:09.682896 2019] [reqtimeout:info] [pid 6506:tid 140538787366656] [client 2a02:c7d:de57:4500:4dd:7bb0:c147:b2ee:51117] AH01382: Request header read timeout
[Tue Oct 08 19:58:19.559173 2019] [mpm_event:debug] [pid 13391:tid 140538644690688] event.c(1123): (104)Connection reset by peer: [client 151.255.53.97:1555] AH00470: network write failure in core output filter
[Tue Oct 08 19:58:20.002771 2019] [reqtimeout:info] [pid 15160:tid 140538644690688] [client 2003:e2:5bc3:2208:adb6:baa2:51b9:1736:56900] AH01382: Request header read timeout
[Tue Oct 08 19:58:42.208150 2019] [reqtimeout:info] [pid 6506:tid 140538737010432] [client 2600:1005:b053:214d:5108:92de:a27f:4eae:60976] AH01382: Request header read timeout
[Tue Oct 08 19:59:15.835428 2019] [mpm_event:debug] [pid 20378:tid 140538686654208] event.c(1123): (32)Broken pipe: [client 111.225.148.112:14290] AH00470: network write failure in core output filter

i.e. nothing but AH00470, and that message appears as well (in fact to higher numbers) during normal operation.

I'm grateful both for ideas how to solve the problem and ideas how to track back the problem to its origin.

Best regards,

Roland