Hi Wadapao,
Shared Configuration can ease the management of sites and applications in Hosting scenarios. It however has its challenges, especially when it comes to updating the machines that are joined in Shared Configuration.
The problem you have reported is not specific to the Database Manager and applies to all modules that IIS ships.
If we allowed you to install Database Manager when in Shared Config, the installer will lay some binaries and schema on one of the machines in your farm. It will also write some configuration into your Shared Config. Since the other machines in your farm don't have the same binaries and schema, it will break your farm. That's why the installation blocks by default when it detects Shared Configuration.
Here are steps you can take to workaround this problem without breaking your deployment:
Step 1: Disable Shared Configuration on each of the machines you wish to update.
Step 2: Install Database Manager (or any other extension) on each of the machines within the web farm.
Step 3: On your master machine, export your configuration.
Step 4: Re-enable shared configuration on all of the machines in your web farm.
The above process can be performed in a cascading fashion:
1. Disable Shared Configuration on machine A
2. Uninstall/install Database Manager on machine A
3. Export the new configuration of machine A to a new shared configuration UNC share (don’t overwrite the existing one)
4. Enable shared configuration on machine A to point to the new shared configuration share
5. Disable shared configuration on machine B
6. Uninstall/install Database Manager on machine B
7. Enable shared configuration on machine B to point to the new shared configuration share
8. Repeat steps 5 through 7 for the rest of the machines in your web farm
Let me know if you need more assistance.