Aportación realizada por Howard Miller

Imagen de Core developers Imagen de Documentation writers Imagen de Particularly helpful Moodlers Imagen de Peer reviewers Imagen de Plugin developers
Firstly, I have moved the discussion to the Hardware and Performance forum. We get asked this type of question a LOT, so you may want to have a look through the forum discussions and see what the answer was previouly.

I would note that "3,000 concurrent users" is a big number. You need to be very clear about what you understand by "concurrent users", what they will be doing and that this number is somewhere near correct. If you get this an order of magnitude wrong then it either won't work or cost you a lot of money (or both). 

My best advice is that if you are asking this sort of question then the best answer is for you to run a much smaller pilot to start with and gain some real-world experience.
Imagen de Core developers Imagen de Documentation writers Imagen de Particularly helpful Moodlers Imagen de Peer reviewers Imagen de Plugin developers
Unless I missunderstand you... you only see a message about the cron if it is NOT working.

Anyway, to be sure, go to Site administration > Server > Scheduled tasks and check the last run times. They should be "recent".
Imagen de Core developers Imagen de Documentation writers Imagen de Particularly helpful Moodlers Imagen de Peer reviewers Imagen de Plugin developers
That doesn't really matter as it may not be in any way comparible. Moodle - and especially some activities - can impose quite a lot of load. So I wouldn't discount it.

Other than that, *something* is different. Even if you have discounted it as the cause. What's that Sherlock Holmes quote....