使用 docker 和卷安装的 crontab 文件不起作用

Question

I'm testing a cron container using docker, this is working at the moment but it's quite inflexible if I want to change the crontab file. I have to remove the container/image and then rebuild so it picks up the new crontab changes

I've been playing around with mounting the crontab file on my windows host but it doesn't get applied. If I open the docker cli and type "crontab /etc/cron.d/crontab then it works.

Any idea how to achieve this?

This is my dockerfile:

# installing cron package
RUN apt-get update && apt-get -y install cron dos2unix tzdata && \
    find /etc/cron.d -type f -print0 | xargs -0 dos2unix

# Set Timezone
ENV TZ="Europe/London"

# installing PHP mysqli extension to talk to MySQL
RUN docker-php-ext-install mysqli

# creating the log file that will be written to at each cron iteration
RUN touch /var/log/cron.log

# copy the crontab in a location where it will be parsed by the system
COPY /cron/crontab /etc/cron.d/crontab
# owner can read and write into the crontab, group and others can read it
RUN chmod 0644 /etc/cron.d/crontab

# Apply cron job
RUN crontab /etc/cron.d/crontab

docker-compose

    cron:
        build:
            context: .
            dockerfile: CRON.Dockerfile
        # run crond as main process of container
        entrypoint: [ "bash", "-c", "cron -f"]                    
        volumes:
            - ./app:/app

I would just add this to the docker-compose file to mount

- ./cron:/etc/cron.d

Then the dockerfile would look like this

FROM php:fpm

# installing cron package
RUN apt-get update && apt-get -y install cron dos2unix tzdata && \
    find /etc/cron.d -type f -print0 | xargs -0 dos2unix

# Set Timezone
ENV TZ="Europe/London"

# installing PHP mysqli extension to talk to MySQL
RUN docker-php-ext-install mysqli

# creating the log file that will be written to at each cron iteration
RUN touch /var/log/cron.log

Answer 1

You can try writing a script where you copy the file that you mounted outside the container to a file inside /etc/cron.d , give permissions to such file, then run the command crontab copied_file.crontab and finally run cron -f . Running this script would be your entrypoint. This is the solution which worked for me

If you want to modify the cron file, just run the same lines of that script but skip cron -f since cron is already running. This will register the new file and install the new crontab.