We don't mount the docker executable , but only the docker.sock file.
The image installs the latest docker-engine to be used as a client through the docker.sock socket.
the image creation always installs the latest docker-engine version to be used as client so normally when the host's docker-engine server is older version it might show an error about API mismatch.
The good news is that docker has this nice env variable DOCKER_API_VERSION which allows newer clients to talk to older servers.
we use supervisor as the cron requires rsyslog so we need to run rsyslog prior the cron daemon so that is uses the rsyslog to send the logs to /var/log/syslog
if you don't need emails for the output from the cron jobs than you don't need the smtpContainer and the MAILTO env # DOMAINNAME is used for the email FROM and TO fields when cron sends the email
all envarionment variables set with the -e or in docker compose will also be set in the crontab file. This solve some weird command failures when we don't have the correct env vars. If you need to set some env vars in the container used to run the cron command you can use something like: CRONTASK_1="* * * * * root docker run debian bash -c "export CUSTOM_ENV=cron && echo '$CUSTOM_ENV 1 run from docker container'"
MANUAL RUN (copy and paster)
the default bridge network doesn't allow communication between containers without using the legacy --link switch so we creat a user defined network docker network create cronApp docker run -d \ --name=smtpContainer \ --net cronApp \ -e DOMAINNAME=domain.com \ -e SMTP_INTERVAL=1m \ -e SMTP_PROCESSING=queue_only_load_latch \ -e SMTP_remote_max_parallel=2 \ -e SMTP_queue_run_max=3 \ -e SMTP_timeout_frozen_after=3h \ vipconsult/smtp docker run -d \ --name=cronContainer \ --net cronApp \ -v /var/run/docker.sock:/var/run/docker.sock:ro \ -e DOMAINNAME=domain.com \ -e DOCKER_API_VERSION=1.23 \ -e SMTP_SERVER=smtpContainer \ -e MAILTOfirstname.lastname@example.org \ -e CRONTASK_1="* * * * * root docker run debian echo 'Cron 1 run from docker container'" \ -e CRONTASK_2="* * * * * root docker run debian echo 'Cron 2 run from docker container'" \ vipconsult/cron
version: '2' services: cron: image: vipconsult/cron container_name: cronContainer volumes: - /var/run/docker.sock:/var/run/docker.sock:ro environment: - DOCKER_API_VERSION=1.23 - SMTP_SERVER=smtpContainer - DOMAINNAME=domain.com - MAILTOemail@example.com - CRONTASK_1=* * * * * root docker run debian echo 'Cron 1 run from docker container' - CRONTASK_2=* * * * * root docker run debian echo 'Cron 2 run from docker container' smtp: image: vipconsult/smtp container_name: smtpContainer environment: - DOMAINNAME=domain.com - SMTP_INTERVAL=1m - SMTP_PROCESSING=queue_only_load_latch - SMTP_remote_max_parallel=2 - SMTP_queue_run_max=3 - SMTP_timeout_frozen_after=3h
docker logs cronContainer docker logs smtpContainer