Send stdout logs from running Docker containers by email.

docker-logtail.sh

#!/bin/sh
# Written by Tomasz Klim, 2019-07-05
#
# This is a simplified, open source version. It relies on $MAILTO variable
# defined in /etc/crontab file for all cron tasks. A better approach would
# be to send emails in dedicated format, to dedicated list of recipients.
#
# Add this to /etc/crontab:
# * * * * * root /etc/local/docker-logtail.sh

if [ ! -x /usr/bin/docker ] || [ ! -x /usr/sbin/logtail ]; then exit 0; fi

for ID in `/usr/bin/docker ps -q --no-trunc`; do
    infile=/var/lib/docker/containers/$ID/$ID-json.log
    offsetfile=/var/lib/docker/tmp/$ID.offset
    /usr/sbin/logtail -f$infile -o$offsetfile
done