Cron container runs out of memory

Preconditions

1. Use --with-cron to generate configs
2. I'm gonna assume a default Magento won't have this issue, but our installation has about 30 packages in the composer.json, so not a big store imo.

Steps to reproduce

1. Start the containers
2. Start the cron (make sure it's enabled in env.php - otherwise you'll be searching like me why it's not working since it's not mentioned in the docs...)
3. Observe the log file

Expected result

1. Happy cron jobs

Actual result

1. Sad cron jobs

What can be investigated is why the cron job thinks it only has 2MB of memory, when PHP was configured for 2GB.

Solution

1. Allocate more memory to the cron by changing the CRONTAB environment to:

CRONTAB: '* * * * * root cd /app && /usr/local/bin/php -d memory_limit=-1 bin/magento cron:run >> /app/var/log/cron.log'

Start with the --with-cron generated configuration, env.php, and the CRONTAB environment command; compare the memory limit used by the cron container with PHP's configured 2GB limit. Reproduce with an installation containing additional Composer packages and verify that cron no longer reports a 2MB limit, using the documented memory_limit=-1 command only as a reference workaround.