Refactoring multiple instances of ecommerce software into single code base

Disclaimer, I am technical support and sysadmin for my开发者_开发技巧 company, not a developer. I'm not after the specifics, simply an idea if what I'd like to acheive is possible or not.

We host hundreds of instances of our in-house classic ASP legacy ecommerce software application and due to countless customisations by clients and ourselves, version management is nightmarish, custom code can't be managed and we've given up releasing new features and mass deploying bug fixes due to the inability to track who needs what patches where.

Parellel to this question I am making management scripts to better automate this though.

What however I'd really like to do is using the miniumum possible effort, port the application code (not the database) to a single code base. Questions I have:

• Can ASP relatively effeciently handle connecting to different databases depending on the host header being called? I plan some basic extension to the routine, get hostheader lookup up db credentials in metadb, set application connection string accordingly logic.

• The application writes a few files to the webserver from the database for caching purposes, I'd like to handle this by emulating this behaviour by writing it to something like /masterapp/customer1/specificfile.htm then changing the references to /specificfile.htm in the code to more like /masterapp/shop name/specificfile.htm. Obviously the routines that write specificfile.htm would write to the new location accordingly. Does this seem reasonable?

• Other webserver-bound store specific contents like images and csv files I need to keep working without URLs changing ideally, can ASP employ logic to redirect get requests for /images/example.jpg to either /masterapp/shop name/images/example.jpg or /shopname/images/example.jpg depending again on host header? Or could that be done via isapirewrite? (which we already use)

I think these are the biggest challenges. I don't need a complete project plan of how to implement each of these things, I just want to know if it's possible. If the answer is 'yes' I should be able to sell my bosses on the development due to saving support time and our in-house developers could hopefully manage this.

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This should be possible and I have achieved similar outcomes with code developed that way from the start. As you are retrofitting this in it's going to be a lot harder, but that's separate to your actual question.

To answer your actual points:

• Presumably your DB connection string is already in a application variable or settings file? If so, you just need some logic in your global.asa Session_OnStart that reads the host header and selects the appropriate DB string. This could be hard coded or you could have a "control" DB that stores sites, their DB strings file paths etc and pulls the details into the session object.

• This is related to the above, pull your cache storage locations from the DB, or have a "directory name friendly" base name for each site, so you can have "/masterapp/" & Session("strSiteBaseName") & "/cache/somefile.htm"

• If you're on IIS7 then you can use the URL rewrite module to handle this, if you're on IIS6 there are 3rd party tools you can get to do URL rewriting for you. Again I have done this so can vouch for it working. If you want to get really clever, you can have your master app create the rewrite files for you and "touch" web.config to get them loaded into IIS.

One "gotcha" you'll have with host headers is remember to handle www and no-www records!

You mentioned custom code as well for each site, I haven't done this in production but have tested outside an app and you can rewrite functions after they've already been declared. You can't have includes with variable names, but you can load in a text file and execute it, so there is a way to have custom functions, or changed core functions specific to an individual instance of your over-arching app.