Crontab-as-code

There are various tools that either wrap crontab, or offer alternatives to it. All I wanted though, was a simple solution to have my scheduled tasks defined as code (checked into a git repo) so that the tasks are reproducible and idempotent, just as Terraform is for IaaS.

All of my scheduled tasks are linked to services (running in docker containers), and I wanted my tasks defined alongside the service which they worked upon. Therefore, I have a directory structure as below:

cwd
 | - app1
 |    | - docker-compose.yml
 |    | - crontab
 | - app2
 |    | - docker-compose.yml
 |    | - crontab 

I then have a small script at the top-level which combines all of the individual crontab files and applies the resultant set to the system crontab:

#!/bin/bash

export CRONTAB_FILES="$(find . | grep "crontab")"

# Re-create all Crontab
echo "# Do not edit this file, it is autogenerated" > tmp_crontab
for CRONTAB_FILE in $CRONTAB_FILES
do
    echo "# From $CRONTAB_FILE:" >> tmp_crontab
    cat $CRONTAB_FILE >> tmp_crontab
    printf "\n" >> tmp_crontab
done

crontab tmp_crontab
rm tmp_crontab
crontab -l

Running this script means that the crontab on my server is now defined as code and checked into my git repo allowing the tasks to be reproducible.