Web SITE publishing, dynamic compilation, smoke & mirrors
- by tbehunin
When you publish a web SITE in Visual Studio, in the dialog box that follows, you are given an option to "Allow this precompiled site to be updatable". According to MSDN, checking this option "specifies that all program code is compiled into assemblies, but that .aspx files (including single-file ASP.NET Web pages) are copied as-is to the target folder".
With this option checked, you can update existing .aspx files as well as add new ones without any issue. When a page, that has either been updated or newly created, is requested, the page gets dynamically compiled at run-time and is then processed and returned to the user.
If, on the other hand, you didn't check that checkbox during the publish phase, the .aspx files get compiled, along with the code-behind and App_Code files in separate assemblies. The .aspx files are then completely overwritten with a line of text that says: This is a marker file generated by the precompilation tool, and should not be deleted! You obviously can't edit an existing page in this scenario. If you were to ADD a new .aspx file to this site, you would get a .Net run-time error saying that the file hasn't been precompiled.
With that background, my questions are these:
Something must be able to determine that this website was published to be updatable (allow dynamic compilation) or not. If it was published as updatable, it must also be able to determine whether a file was changed or added, so it can do a dynamic compile.
Who makes those determinations? IIS? ASP.NET worker process?
HOW does it make those determinations? If I had the same website published in both of those scenarios, could I make a visual determination that one is updatable and the other is not? Is there some bit I can look at in the assemblies using Reflector to make that determination myself?
In addition to answering those questions, what also might be helpful would be information on the process flow from when a resource is requested to when it starts being processed, not necessarily the ASP.NET Page Lifecycle, but what happens BEFORE ASP.Net worker process starts processing the page and firing off events. The dynamic compilation appears to be smoke and mirrors. Can someone demystify this for me?
