AWS Cron Expressions

It's similar to Linux cron, but there's a ? involved.

They thought it would be too confusing to put * on both Day of Month (column 3) and Day of Week (column 5). So, one can be * but the other must be ?.

# e.g.
cron(0/5 * * * ? *)
     ^ every five minutes
         ^ every hour
           ^ every day of the month
             ^ every month
               ^ Day of week is unknown
                 ^ Every year

# e.g. once an hour, but only at 12-6 PM UTC
cron(0 8-17 * * ? *)

# e.g. once an hour, but only at 12-6 PM UTC and only on Tuesdays
cron(0 8-17 * * TUE *)

# e.g. once an hour, but only at 12-6 PM UTC and only on Work days
cron(0 8-17 * * MON-FRI *)

Other examples:

https://docs.aws.amazon.com/AmazonCloudWatch/latest/events/ScheduledEvents.html