What is a scalable way of creating cron jobs on Amazon Web Services?
There is no straight forward solution to your problem .You have to proceed step by step with some plumbing along the way .
Event management
1- Create a lambda function that creates a cloudwatch schedule.
2 - Create a lambda function that deletes a cloudwatch schedule.
3 - Persist any event created using dynamodb
4 - Create 2 API gateway  that will invoke the 2 lambda above.
5 - Create anohter lambda function (used by cloudwatch) that will invoke the API gateway below.
6 - Create API gateway that will invoke the website via http request.
When the user creates an event from the app, there will be a chaining calls as follow :
4 -> 1,3 -> 5-> 6
Now there are two other parameters to take into consideration :
Lambda concurrency: you can't run simultaneously more than 1000 lambda in same region.
Cloudwatch: You can not create more than 100 rules per region . Rule is where you define the schedule.
This is my first question so I appologize if it's not the best quality.
I have a use case: User creates a monitoring task which sends an http request to a website every X hours. User can have thousands of these tasks and can add/modify and delete them. When a user creates a task, django signals create a Celery periodic task which then is running periodically.
I'm searching for a more scalable solution using AWS. I've read about using Lambda + Cloudwatch Events. 
My question is: how do I approach this to let my users create tens of thousands of these tasks in the cheapest / most scalable way?
Thank you for reading my question!
Peter