Dockerfile 例子：
FROM alpine
# Copy script which should be run
COPY ./myawesomescript /usr/local/bin/myawesomescript
# Run the cron every minute
RUN echo '* * * * * /usr/local/bin/myawesomescript' > /etc/crontabs/root
CMD ['crond', '-l 2', '-f']
如果只关心周期性运行，可以使用重启机制来实现
docker-compose.yml 例子：
version: '3.3'
services:
letsencrypt:
image: czerasz/letsencrypt-companion
deploy:
restart_policy:
condition: any
# Run every day
delay: 1d
...
