Installation Guidelines for User-editable Configuration

Installation Guidelines for User-editable Configuration

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A common problem with installations is user-editable files and registry keys. Configuration of this nature is a problem for every installer technology, but here are some guidelines to help developers overcome problems like users' preferences being reset during repair.

Windows Installer is a data-driven installation technology. Installing a patch on a Windows Installer installation package, an .msi file, is just a repair operation with some new data transformed by the patch. When this occurs, any updated features, or features explicitly listed in the REINSTALL property, are reinstalled, along with their components and all their components' resources. For registry values, there is no versioning like there is for files, so if a reinstalled component includes registry values they will be overwritten.

For registry values, only defaults should be written – if at all – to a location appropriate for the installation. If the installation must be elevated already, writing these values to HKEY_LOCAL_MACHINE is appropriate. For per-user installations, you might have a separate registry key for defaults from which the application only reads. For per-machine installations, an application – as already detailed in several guidelines for Windows applications – should only ever read from HKLM unless it is some type of administration application. If your per-machine application supports global configuration data, use the same approach as for per-user installations of storing defaults in one key and overrides in another. One suggestion in this case is to use a key under HKEY_LOCAL_MACHINE\Software\Policies\[Manufacturer] for defaults to be overridden as policy dictates – the location where .adm and .admx files for system policies will typically write – and HKEY_LOCAL_MACHINE\Software\[Manufacturer] for defaults that should not be overwritten. The latter may not even be necessary if in code you specify defaults when reading registry values. You might install values in this location when configuring differences between installations or machines based on machine data at the time of installation.

For non-versioned configuration files, you should use custom actions that modify only sections of those files. Conflict resolution should be considered carefully, based on the importance of your update versus the users' preferences. The machine.config file in the Microsoft .NET Framework is an example of a file – an XML configuration file, to be exact – that should be modified and never replaced. When the mobile extensions for ASP.NET first became available, their installation merely modified that file appropriately. It's also advantageous in Windows Installer to keep such configuration changes data-driven, so that you can easily change key information in a patch transform without having to repackage an updated custom action binary, which can be difficult to manage with multiple active patches for a product. This is the behavior of the WiX custom actions and tables for XML files, and it's recommended you use these community-supported custom actions and tables if appropriate for your application installation needs.

If you do write your own custom action to update configuration files based on installation options, make sure that you update the creation and modification timestamps for these files so that they are the same. If your custom action does not do that, the modification timestamp would be newer than the creation timestamp and Windows Installer would not update, by default, that non-versioned file. Hash checks on non-versioned merely help Windows Installer determine if the file in the patch needs to be installed, comparing the hash values of both the file on disk and in the installation package.

Following these installation guidelines for user-editable configuration can benefit both you and your users by reasonably maintaining their preferences while affording you the opportunity to update configuration when necessary.

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  • Hi,

    We are now in a stage where we want to change all our installation to be Wix / Wise (and not Visual Studio deployment setups) and to take advantage of msp between versions.

    Indeed as you wrote above, we also have some files that are user / program editable:

    1. Web.Config - Few keys are veing changed by an outer program that the admin can run

    2. Resource files (whether compiled / not) - can be edited with an application that was created called Captino Editor that marely edit the values of different caption in the compiled / non compiled resources.

    3. Registry that can be written by the customer

    This as you wrote is a very tricky issue that although i read your article still facing a diffficult issue:

    During the life cycle of the application we update the configuration files mention above - so every MSI we create will surly contain the new files - thus creating a patch will not be an easy task because the diffrence between the two files will surly contain the files that the user can edit in between two versions and installing a patch will overwrite the file (if the user edited the values they will be overwriter by the patch).

    Today the deployment project simply copies the files to the MSI (visual studio setup project) and the developer does almost nothing to create a new version - simply get latest and compile.

    Do you have an example of a project that has all 3 file types that has some custom actions that cause the files to incremental updated between msi?

  • As for the web.config file, use the XML tables in WiX. For the RC files, if these are part of an example consider moving them to a separate MSI for just those samples that doesn't register itself as a project. Basically, you'd be created a sort of self-extracting ZIP. Don't schedule the Publish* actions to accomplish this. As far as the registry, leave that up to your application. Feel free to put defaults - if even necessary (basically, you only need things that are based on setup locations or other setup data) - but the user-editable portions should not be written, removed, or otherwise updated by your setup. That's a task for your application (or just expect users to do it manually).

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