Question
Answer and Explanation
A linked server, in the context of a Data-Tier Application Package (dacpac), does not represent the actual configuration of a linked server on a SQL Server instance.
Instead, a dacpac stores the database schema and related objects required to deploy a database. Linked server definitions, which pertain to instance-level configurations and involve external data sources, are typically not included within the dacpac itself.
Here's a more detailed breakdown:
What is a Linked Server?
In SQL Server, a linked server allows you to execute queries against remote data sources, including other SQL Server instances, Oracle databases, or even data in flat files. It provides a mechanism for seamlessly accessing data spread across multiple servers.
Why Linked Servers Are Not in DACPACS:
1. Instance vs. Database Scope: Linked servers are SQL Server instance-level configurations. A dacpac, by definition, encapsulates database-specific objects like tables, stored procedures, views, and functions.
2. Environment-Specific Configurations: Linked server definitions often vary based on the environment (development, testing, production) and the specific network configurations. Including them directly into a dacpac would make deployments less portable and flexible.
3. Security Concerns: Linked server configurations involve credentials and security settings that should be handled separately and managed carefully. Embedding sensitive data like usernames and passwords directly within a dacpac is a security risk.
How to Handle Linked Servers in Deployment:
When deploying a database that relies on linked servers, the linked server configurations must be managed separately using other tools or scripts before or after the dacpac deployment. Common approaches include:
1. SQL Scripts: Use SQL scripts to create linked servers as part of your deployment process. These scripts can be parameterized to adapt to different environment settings.
2. PowerShell/SQL Server Management Objects (SMO): PowerShell scripts using SMO can be used to automate the creation and management of linked servers.
3. Configuration Management Tools: Tools like Ansible, Chef, or Puppet can be used to manage instance-level configurations, including linked server setups.
4. Manual Setup: For smaller or less frequent deployments, the linked server configuration can be set up manually using SQL Server Management Studio (SSMS).
Summary
While a dacpac encapsulates database schema, a linked server is an instance-level object that needs to be managed separately, often using scripts or external tools. Understanding the distinction is important for planning robust and maintainable database deployments.