Create one big web project or split some features into web services?

At what point (if at any) does it make sense to take some of the features of a .NET web application and split them into separate web services?

For example, we have a very large web application that also calls a series of long running operations (our core business logic). We also have a dll with client-specific custom features that is called directly from the web project. Sometimes we need to move very quickly to change these client functions, often in hours.

However, if we make开发者_StackOverflow中文版 a change to the client-specific features (or an emergency change to the core features) and publish a new project, then it would kick all the users out the system as the app restarts. It would seem like there's a better way ... but I'm not sure what it might be ...

First of all, it makes sense to remove everything from the web project that is not involved with the UI. Put that in separate class libraries.

Do not create web services unless some other application will be calling them. Simply placing the code into separate projects will be enough. Web services should only be created if they are a requirement.

I think it makes sense to create service app (not like Web Service, but more like Windows Service). You could communicate between your webapp and service app using Message Queue.