Is switching app.config at runtime possible?

Question

Is there a way at runtime to switch out an applications app.config (current.config to new.config, file for file). I have a backup/restore process which needs to replace its own application.exe.config file. I have seen this post but it does not answer how to do this at runtime.

Answer 1

Are you able to restart the application when you detect that you need to switch files? If so, it's just a matter of switching the files and restarting. Now, the tricky bit is if .NET keeps the app.config file open while the program is running. I suspect it doesn't, but if the most obviously approach fails, I suggest you have a second application (cfgswitcher.exe) which waits for the process with a PID specified on the command line to terminate, then switches config files and relaunches the original process. Then your app would just need to launch cfgswitcher.exe (passing in its own PID as a command line argument) and terminate.

As I say though, it's worth trying the more obvious approach first.

EDIT: If you can't restart the application (or even part of it in a new AppDomain) then various aspects of app.config (assembly bindings etc) can't be changed. If you're only interested in your own configuration sections changing, then I suggest you store them in a separate config file and reload them whenever you want to.

Answer 2

Look at the events available to you on the ApplicationSettingsBase class. There are PropertyChanged & SettingChanging that may give you what you need.

You could also watch the file and if it has changed call the reload method to get the new settings.

Answer 3

I don't think it is possible at all to switch the configuration at runtime without restarting, so if you can't apply Jon's approach, you should try to come up with an other approach.

Anyway, maybe it's just me not having enough information about your scenario, but this kind of feels fishy.

Are you sure that swapping the configuration file is the best way to achieve whatever requirement you need to meet? I mean, this is quite an uncommon thing. If I were you, I would try to come up with some other approach.

Answer 4

Turns out I can swap the .config file for the new one and do a ConfigurationManager.RefreshSection(...) for each section. It will update from the new .config file.

Answer 5

Microsoft .NET's app.config is not designed for your scenario, as well as many others. I often encounter a similar need, so I have spent a lot of effort designing a solution.

1. Redesign to use app.config only as a configuration bootstrap: specify where to find the rest of the real configuration data. This information should almost never change, so there is no need to handle file watching or application restarts.

2. Pick an alternate location for the real configuration data: a file, a database, perhaps even a web service. I prefer a database most of the time, so I create a configuration table with a simple structure that allows me to store my data.

3. Implement a simple library to wrap your configuration access so that you have a simple API for the rest of your application (via dependency injection). Hide the usage of app.config as well as your real configuration storage location(s). Since .NET is strongly-typed, make the configuration settings so--convert each string retrieved into the most-specific type available (URL, Int32, FileInfo, etc.).

4. Determine which configuration settings can be safely changed at runtime versus those that can't. Typically, some settings need to change along with others, or it simply makes no sense to allow them to change at all. If all your configuration data can safely change at runtime, then that makes things easy, but I HIGHLY doubt such a scenario. Hide the changeability and interdependencies of the configuration settings to the extent possible.

5. Design the response to the unavailability of your real configuration data. I prefer to treat the absence of any configuration setting as a fatal error that aborts the application, unless I can identify a usable default. Likewise, I abort in the absence of the configuration storage container (file, database table, etc.).

Enjoy, and best wishes.