Interview Questions

Internet Information Services is Microsoft’s web server for Windows. It receives HTTP(S) requests through the kernel driver HTTP.sys and serves static files or hands requests to applications such as ASP.NET Core (via the ASP.NET Core Module) or ASP.NET Framework running in worker processes.

An isolated container of one or more w3wp.exe worker processes with its own identity, .NET CLR setting, pipeline mode and recycling rules. Separate pools keep one crashing or slow app from affecting others.

The combination of protocol, IP address, port and host name that IIS uses to decide which site receives a request — for example https, All Unassigned, 443, shop.example.com with SNI.

Install the .NET Hosting Bundle, publish the app, create a site pointing at the publish folder, set its app pool to “No Managed Code”, and let the generated web.config load the ASP.NET Core Module (in-process by default). Grant the pool identity read access to the folder.

The default, least-privileged virtual account IIS creates per pool, named IIS AppPool\PoolName. You grant it file, folder or SQL permissions instead of using a shared domain account.

It starts a new worker process and gracefully shuts down the old one — by default every 1,740 minutes and after 20 minutes idle. In-memory sessions and caches are lost, and the first request after a recycle can be slow.

Copy the build output to the site folder, install the URL Rewrite module and add a rule that rewrites requests for non-existent files and folders to /index.html, while leaving /api and real files untouched.

500.19 means IIS cannot read web.config (bad XML or a missing module such as URL Rewrite). 500.30 is an in-process ASP.NET Core start-up failure; 502.5 is an out-of-process start failure. Check the Event Viewer, enable stdout logging in web.config and run the app from the command line to see the real exception.

A per-request diagnostic log (FREB) that records every module, event and timing for requests matching rules such as status code 500 or time taken over 5 seconds. It shows exactly where a request failed or slowed down.

Use Application Request Routing (ARR) with URL Rewrite on a front-end server to create a server farm with health checks, or use a hardware/cloud load balancer. Keep apps stateless or use a shared session store, and share Data Protection keys.