Move to an External Cron

[kingkool68]

Currently each machine runs a WP CLI script every minute to manage cron events (See b279d5c)

The problem with doing this in production is we have multiple servers running at a given time which means the cron events are triggered multiple times per minute. The best way to resolve this would be to use an external cron service that pings one URL so the cron job is only triggered once per minute regardless with how many machines are running in production.

Possible solutions:

• https://cron-job.org/: Free but we don't control it
• Using an AWS Lambda function + CloudWatch to replace cron: Costs would be minimal and we control it. See http://brianstempin.com/2016/02/29/replacing-the-cron-in-aws/

Either solution would also require us to set-up a PHP script that the external cron would hit so whenever we add a new site we don't need to manually update the external cron script. See https://tribulant.com/blog/wordpress/replace-wordpress-cron-with-real-cron-for-site-speed/