I have an application developed in PHP + MYSQL using CodeIgniter. Currently we have about 3000 active users using the application daily, we have around 130,000 pageviews per day. The system does not use many resources, which is most commonly used is HTTP and reading / writing in MYSQL. My question is: What is the best instance to be hired at Amazon? What setting do you suggest me? An important we are to the brand alcaçar 50,000 users in the next six months.
The best instance is the one you can afford that isn't overloaded when busy. You should be monitoring CPU load and memory usage using a tool like Munin to be sure you're not running out of headroom.
If you're using Amazon RDS to handle your database, you can add multiple front-end web servers to handle the load.
There's no magical size that works "best", but the c1.medium is pretty good value.