Most of the problems you run into occur during the early configuration stages while you test your server before production. These problems are usually easier to deal with, because you are mentally prepared for the challenge, and more importantly, because Nginx points out syntax or configuration errors on startup. It is, on the other hand, much more difficult to identify the cause of malfunctions while your websites are actually in production stages. But once again, Nginx saves the day: if you properly configure log files (both access and error logs) and take the habit of reading them regularly, you will find that problem solving is made easy.
This concludes our journey with Nginx, during which we have been through a large number of subjects, from basic mechanisms of the HTTP server to web application deployment and troubleshooting. If you are interested in becoming a true Nginx expert, we recommend further reading: Mastering Nginx by Dimitri Aivaliotis, and NGINX High Performance...