Dockerize 'at' scheduler - docker

Question

I want to put at daemon (atd) in separate docker container for running as external environment independent scheduler service.
I can run atd with following Dockerfile and docker-compose.yml:
$ cat Dockerfile
FROM alpine
RUN apk add --update at ssmtp mailx
CMD [ "atd", "-f" ]
$ cat docker-compose.yml
version: '2'
services:
scheduler:
build: .
working_dir: /mnt/scripts
volumes:
- "${PWD}/scripts:/mnt/scripts"
But problems are:
1) There is no built-in option to reditect atd logs to /proc/self/fd/1 for showing them via docker logs command. at just have -m option, which sends mail to user.
Is it possible to redirect at from user mail to /proc/self/fd/1 (maybe some compile flags) ?
2) Now I add new task via command like docker-compose exec scheduler at -f test.sh now + 1 minute. Is it a good way ? I think a better way is to find a file where at stores a queue, add this file as volume, update it externally and just send docker restart after file change.
But I can't find where at stores its data on alpine linux ( I just found /var/spool/atd/.SEQ where at stores id of last job ). Anyone knows where at stores its data ?
Also will be glad to hear any advices regarding at dockerization.
UPD. I found where at stores its data on alpine, it's /var/spool/atd folder. When I create a task via at command it creates here executable file with name like a000040190a2ff and content like
#!/bin/sh
# atrun uid=0 gid=0
# mail root 1
umask 22
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin; export PATH
HOSTNAME=e605e8017167; export HOSTNAME
HOME=/root; export HOME
cd /mnt/scripts || {
echo 'Execution directory inaccessible' >&2
exit 1
}
#!/usr/bin/env sh
echo "Hello world"
UPD2: the difference between running at with and without -m option is third string of generated script
with -m option:
#!/bin/sh
# atrun uid=0 gid=0
# mail root 1
...
without -m :
#!/bin/sh
# atrun uid=0 gid=0
# mail root 0
...
According official man
The user will be mailed standard error and standard output from his
commands, if any. Mail will be sent using the command
/usr/sbin/sendmail
and
-m
Send mail to the user when the job has completed even if there was no
output.
I tried to run schedule simple Hello World script and found that no mail was sent:
# mail -u root
No mail for root