The code seems to be quite stable as I had to fix only minor bugs during the last 10 month. For performance reasons I decided to kick the Basscss toolkit and replace with some own lines of CSS to reduce the overhead when loading the homepage.
In the graph you can see the Nginx requests per second from the last month. The API currently handles about 5-10 requests per second in average. That's about 600.000 requests per day. There's still room for more ;)
During peaks there are 250-500 requests per second. But I recognized that these peeks mostly request the same IP over and over again. This most probably happens when a site using the API get's brute-forced by a bot. To handle this the nginx configuration only allows 30req/sec from one IP.
So all in all the project runs very well. Let's see where it is going.