API to find the number of instances run by hour - AWS

I am looking for API that can return number of insta开发者_如何学编程nces that run during the course of the day for each of the hour.

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If it was my task, I would create a php script that runs in cron job every hour and record EC2 instances information (Running number of instances a part of that) in the database.

Then just query the database to with the right parameters.