I have a web.config file that references a rewrites.config file that is used by the inbuilt IIS Rewrite module. However my rewrites.config file is larger than 250kb, so i have followed the advise on this post. However it appears that in IIS 8.5 (Windows Server 2012) these keys are ignored. I've search the interwebs and haven't been able to find much on IIS 8.5, anyone got any advice on how to increased the maximum.config size? Or alternatively split rewrites.config into smaller files?
You can just create the key.
Right click on the parent node in REGEDIT - add a new Key called Configuration. Then add a new DWORD for MaxWebConfigFileSizeInKB (you'll probably want to switch to the decimal view) and set the value in KB.
I've just tested this on a rewritemap.config file 753kb in size on a server running IIS8.0 on Windows Server 2012 (I'm making an assumption here that this won't be terribly different from IIS 8.5). You'll need to set the appropriate key depending on whether this is 64bit or 32bit (see here). If in doubt set both. I can confirm that this value is being used since turning the value down to (for example) 10 triggers the error again.
Don't forget to restart the app pool.
来源：https://stackoverflow.com/questions/24489866/setting-maxwebconfigfilesizeinkb-in-iis8-5