Free APM Software

I have a few Web Apis that I have written for a side project, and I am noticing there is a lag in performance when I deploy them to Azure. They are running a low version of the App Service because I want to not spend as much, but I want the optimal performance of the app given the environment it will exist in. At my work, we do a lot of things with App Dynamics and I was wondering if there are any open source or free tools that offer similar things. I would like to be able to run a few tests, and see some metrics about different stack trace calls and want are the pain points of the app so I can come to a resolution. Do such tools that aren't insanely expensive exist? Are there some things I can do with Visual Studio online or within Azure itself?