Earlier this year, I built a .Net Core Web Application and deployed it on IIS 7.5. I noticed right away that it was extremely slow on initial load. This was confusing because I tested deployment to Azure and the performance was great. I struggled to figure out why it loaded so slowly but all of my .Net Framework sites ran quickly.

I struggled to find an answer for a long time, but while reading through documentation while setting up another application I came across this bit of information:

http://cdn.rssbus.com/help/ARC/mft/pg_serveriis7dot5.htm

Preloading Applications

You can make use of the preloading feature to have applications running before users connect. In your ApplicationHost.config, add the preloadEnabled attribute to the <application> element associated with the application. The application node is a child element of the sites node:

<sites>
<site name="Default Web Site" id="1">
  <application path="/rssbus" applicationPool="DefaultAppPool"  preloadEnabled="true">
  
  ...

When PreloadEnabled is set to true, IIS will simulate a user request to the default page of the website or virtual directory so that the application initializes.

While it technically is a bit of a workaround since it doesn’t solve the root problem I experience with preloading, it has kept my application loading quickly since I enabled it.