Web Service or DLL?

Question

I'm creating an app that needs to be accessed by both a web front end hosted on an internal network and also run as a scheduled task. Nothing will need to be accessed outside of our internal systems and once the app is up and running we don't envision anything changing for some time.

My initial thought is to create a DLL encapsulating the bulk of the necessary functionality and then call it via both a Web Forms interface for manual execution, and a console app running as an automated (daily) scheduled task.

Another suggestion has been to expose a Web Service for the core functionality instead, but as the app will never need to be called by an external resource I think the extra effort required in implementing a Web Service might not be worth the hassle. The DLL solution should also be substantially faster(?).

My question is which route would you choose? Are there any pros/cons that I haven't covered? Any glaring omissions?

Disclaimer: I'm new to .Net but due to one of our developers being involved in a serious accident I've been asked to step up to the plate.

Answer 1

Personally, I say go with the DLL. It will be fast and simple.

With a web service, you will need to think about your network, firewalls, performance, etc. It also makes it harder to debug since you won't be able to step into the web service from your clients, you will have to set breakpoints on both sides of the calls.

The other problem with web services for you is that you need to be much more robust handling failures. With a DLL, you know a call to a method is going to succeed, but with a web service, you will need to be prepared for that call to fail or time out whenever you make any call across.

Lastly, if you find a need for a web service at a later date, you should be able to fairly easily convert the DLL into a web service with minimal retrofitting.

Answer 2

Right now there is no need to create a webservice. You just would have to maintain an other IIS service on your server. If you later on create some interface that will need that DLL you can simply refer to it. So there is no need to do it preventative.

Answer 3

You're right, web services are a lot of hassle from experience and much slower. I suggest - do a PONO (plain old .net object), but use interfaces. Look into Spring.NET framework - it can export this object for you as whatever type of (web) service, so you don't need to do the plumming. On the client side, you can also use spring to do the dependency injection and decide if you want in-process DLL or web service implementation, just by changing value in the config file. Also Spring has Quartz scheduler integration, you might want to look into it too.