Shared configuration in IIS allows multiple servers to use a centralized applicationHost.config file, ensuring consistency across a web farm. 1. It enables all servers to point to a shared configuration location. 2. Setup involves using a UNC path, enabling the feature in IIS Manager, and importing encryption keys. 3. Common issues include permission errors, config conflicts, and key mismatches. 4. Avoid it when using complex DevOps pipelines or role-specific servers where alternative tools like Ansible or PowerShell are more suitable. Proper setup with attention to permissions and encryption is crucial for success.

When you're managing multiple IIS servers in a web farm, keeping configuration consistent across all servers is key to smooth operation. Doing this manually isn’t just time-consuming — it’s error-prone. That’s where shared configuration comes in handy.

What Is Shared Configuration in IIS?

Shared configuration allows multiple IIS servers to use the same applicationHost.config file and other related files. Instead of maintaining separate configurations on each server, they all point to a central location for these settings.

This feature is especially useful in environments with load-balanced websites or when you're scaling out horizontally. It ensures that any changes made to the configuration are instantly reflected across all servers using that shared setup.

Note: This doesn’t replace centralized management tools like Web Farm Framework or PowerShell Desired State Configuration — but it’s a lightweight option for smaller setups or specific needs.

Setting Up Shared Configuration

To enable shared configuration, follow these steps:

• Make sure all servers are running the same version of IIS and Windows.
• Choose a central file share (like a UNC path) where the shared config files will live.
• On each server, open IIS Manager → Click the server node → Double-click "Shared Configuration".
• Use the wizard to import the configuration from the central location.
• Check the box for “Enable shared configuration” once imported.

During setup, you’ll be prompted to provide credentials that IIS will use to access the shared folder. It's best to create a dedicated account with read permissions for this purpose.

Also, encryption keys must be exported from the first server and imported into others. Without matching keys, encrypted sections in the config file won’t work properly across servers.

Common Issues and How to Handle Them

Even with a solid setup, a few common issues can pop up:

• Permissions: If IIS can’t access the shared folder, the site might fail to start. Double-check the account used for accessing the share has proper read rights.
• Configuration Conflicts: If there are local settings conflicting with shared ones, unexpected behavior may occur. Always test configuration changes in a controlled environment before pushing them live.
• Encryption Key Mismatch: If keys aren't correctly exported and imported, sensitive settings like connection strings won’t decrypt properly on other servers.
• File Locking or Sync Delays: When making real-time edits, ensure the shared config file isn’t locked by another process. Also, if you’re using sync tools like DFS or Robocopy, make sure they're not introducing delays.

One thing people often miss is ensuring that the administration.config file is also included if custom IIS manager settings or delegation rules are in place.

When Not to Use Shared Configuration

While shared configuration works well in many scenarios, it’s not always the best fit.

For example, if your environment uses complex deployment pipelines or infrastructure-as-code practices, you might prefer syncing configs via tools like Ansible, Puppet, or CI/CD scripts. Those methods offer more control and traceability.

Also, if you have different roles assigned to different servers (e.g., some handle APIs, others serve static content), applying a one-size-fits-all config might introduce unnecessary complexity or security risks.

In such cases, consider alternatives like centralized management through Web Deploy or scripting with PowerShell.

Basically, shared configuration in IIS helps keep things consistent across a web farm without needing third-party tools. It’s straightforward once set up, but don’t skip the small details like key export or permissions — those are easy to overlook but critical for it to work right.

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