Backing up and restoring IIS 7.0 shared configuration

I blogged a long time back about using AppCmd to back up and restore IIS 7.0 server configuration.

Bill also just posted about backing up and restoring configuration, where he does a great job of telling you why you need to make backups and the options you got between manual AppCmd backups and leveraging automatic Configuration History service backups.

This reminded me of a question I often get about backing up and restoring configuration when IIS 7.0 is being used in the Shared Configuration mode.  In this mode, the applicationHost.config file is stored on a UNC share to allow multiple IIS 7.0 servers to share a single configuration file.

Let me answer this question by way of illustrating what happens when you run "AppCmd Add Backup" when the IIS 7.0 server is using local configuration (default), vs shared configuration.

In the local configuration case, the tool will back-up the following files in the %windir%\system32\inetsrv directory:

1. config\applicationHost.config
2. config\administration.config
3. config\redirection.config
4. config\metabase.xml
5. config\mbschema.xml
6. All custom schema files under the config\schema directory

In the shared configuration case, the tool does the same thing.

So, what’s my point? It’s simply that AppCmd backup commands always work with backups of the local server configuration.

This means that in the shared configuration case, the tool WILL NOT back up or restore the configuration located on the UNC share. However, it will back up and restore the local redirection.config file, which contains the details about where the shared configuration file is located.

So, if you were using local configuration at the time of backup, then moved to shared configuration, and then restored the backup, you’ll be back to your local configuration. If you were using shared configuration at the time of backup, then moved to local, then restored, you’d be back to using shared configuration (whatever it may be at this time), and your local applicationHost.config will be reset to the one saved at time of backup.

There is a specific reason for this design.  Imagine this scenario – you have a web farm with multiple servers using a single shared configuration file.  At some point, someone starts having trouble with one of the servers, and restores a prior configuration backup – all of a sudden, all other servers are falling over because their configuration has been reset to a configuration state that is local to the one server. Besides the fact that this could be unexpected and undesired, it could also cause all kinds of serious issues, including encryption key mismatches and configuration for features that are not installed on other web farm servers.

In addition to this, be aware that the Configuration History service will not back up configuration when in shared configuration mode.

So, moral of the story is, when using shared configuration, it is your responsibility to manage the backups of the shared configuration files.

With that in mind:

* DO perform manual backups with AppCmd (or use scheduled tasks, etc) to back up the local state even when using shared configuration. This way, you can restore the redirection.config details later if needed.

* DO perform manual backups of the shared configuration each time you make changes (or on a regular schedule), and perform manual copy of those files to the share to restore the web farm’s configuration.

* DO NOT expect to restore the web farm’s configuration by using AppCmd restore backup commands.

You can still depend on the local backup facilities to restore your server to its original local state, or restore the shared configuration settings as needed.

The only caveat to this is that if you are directly sharing configuration of one of the servers to other servers (so it’s effectively local for the “master” server), then backup/restore operations on that server will affect the entire web farm. However, I do not generally recommend doing this has its own set of limitations out of the scope of this post.

Hopefully this clarifies things a bit.

Thanks,

Mike