We are working on an ASP.NET 5 Web API project that is in production now but we are experiencing an issue where it becomes unresponsive intermittently throughout the day.
A few notes about the application architecture. It is an ASP.NET Web API project using a MariaDB database on a separate EC2 instance within the same private network. The connection string uses the private IP of the database server to avoid any name resolution issues. The site is hosted via IIS 10.
The application itself has been developed carefully following the best practices provided by Microsoft. Heavy focus on async operations, minimizing query response times and offloading more expensive operations into background services.
The app is extremely responsive. It performs with sub 100ms responses on almost all requests, even the more complicated requests, and all the way up until it becomes unresponsive this high level of performance remains the same. We tend to see between 10-30 requests per second and 300-500 select queries per second at peak usage so not too extreme. However, randomly (2-3 times over a 24 hour period) it will begin hanging on requests and simply not respond to the request. During this time, the database is still extremely responsive and we are never over 300 connections out of our 512 connection limit.
The resources on the application server itself are never really taxed much at all. The CPU never gets above ~20% and the memory usage sits around 20-30%.
If I were to stop the site in IIS and start it again while this is happening, it will quickly come back online. If I don't it will be down for a few minutes until IIS finally kills it due to a failed health check. There are no real errors generated as a response to the issue other than typical errors caused by the hanging of the process such as connection terminated errors. The only thing I have seen before that gave me pause was the fact that there a few connection timeouts when getting the connection from the pool, but like I said, the connections to the server are never close to the limit.
Also, this app and version has been in production for months and it wasn't until the traffic volume started to grow that we started seeing these issues. At this point, I am at a loss for next steps of troubleshooting and I'm seeking suggestions.
