Understanding Contained Databases in SQL Server
As businesses grow and technology evolves, the ability to streamline moves and upgrades becomes increasingly important for maintaining efficiency and minimizing downtime. One of the key strategies database administrators can employ to achieve this is through the implementation of contained databases in SQL Server.
Contained databases are an innovative feature first introduced in SQL Server 2012 and refined in subsequent versions. They offer a method to isolate the database from certain SQL Server instance-level details, simplifying the process of moving a database from one server to another. In this blog entry, we’ll dive deep into the concept of contained databases, their benefits, potential drawbacks, and how to effectively use them to streamline database-related operations.
What is a Contained Database in SQL Server?
The term ‘contained database’ refers to a database that is isolated in such a way that it does not depend on the environment in which it resides for its configuration. In other words, a contained database includes all the settings and metadata required to define the database without relying heavily on server-level objects or configuration settings in the SQL Server environment.
Contained databases facilitate the movement of databases across different SQL Server instances because it minimizes issues related to SQL Server logins, linked servers, and other instance-level dependencies that typically hinder database portability. With the advent of cloud solutions and the growing need for robust database systems, contained databases have become a significant asset for rapid scalability and flexibility.
Benefits of Using Contained Databases
There are several advantages to using contained databases that promote better manageability and elasticity. These benefits include:
- Ease of Move and Upgrade: Contained databases can be detached and attached to another SQL Server instance with relative ease since they hold all necessary configurations within them. This significantly streamlines operations during moves or upgrades.
- Reduced Configuration Complexity: By encapsulating most of the configurations needed to persist the database, there is less risk of overlooking critical settings and thereby reduces the room for errors when configuring a new SQL Server instance.
- Improved Security: With user authentication being contained within the database itself, there are fewer security loopholes associated with server-level authentications and dependencies.
- Portability: The portable nature of a contained database makes it easier to transfer databases between development, testing, and production environments or even between on-premises and cloud-based infrastructures.
In addition to these core benefits, using contained databases can lead to simpler disaster recovery processes, improved multi-tenancy for hosting providers, and a generally more agile infrastructure.
Potential Drawbacks of Contained Databases
While contained databases boast several benefits, there are also implications to consider that might pose challenges in some scenarios. These include:
- Feature Limitations: Some of the SQL Server features are not currently supported with contained databases. It’s essential to verify whether all your required features will work in a contained environment.
- Comprehensive Testing Requirement: Due to the change in dependencies and behavior, extensive testing is required to ensure compatibility and that no functionality is lost during migration to contained databases.
- Potential for Orphaned Users: Although-contained databases aim to encapsulate users and permissions, careful management is needed to avoid orphaned users when databases are moved.
- Version Compatibility: Not all versions of SQL Server support contained databases, which could limit your ability to use this feature depending on your environment.
Understanding these potential drawbacks allows SQL Server professionals to make informed decisions about whether and how to implement contained database features in their systems.
Implementing Contained Databases in SQL Server
To create and use contained databases, you must follow certain steps to ensure a successful setup. Below is an overview of the implementation process:
Enabling Contained Databases
The first step to using a contained database is to enable the feature on the SQL Server instance. This can be done using the SQL Server Management Studio (SSMS) or running a simple SQL command as shown below:
EXEC sp_configure 'show advanced options', 1;
GO
RECONFIGURE;
GO
EXEC sp_configure 'contained database authentication', 1;
GO
RECONFIGURE;
GO
Once the feature is enabled, you’re set to create a new contained database or convert an existing one into a contained database format.
Creating a New Contained Database
Creating a new contained database is much like creating any other SQL Server database, with the additional step of specifying containment type at creation. You can use the SSMS graphical interface or a SQL script like the one below:
CREATE DATABASE [YourDatabaseName] CONTAINMENT = PARTIAL;
GO
When the containment type is set to PARTIAL, SQL Server knows to allow for the creation of contained database users for both Windows and SQL authentication types.
Converting to a Contained Database
If you’re working with an existing database that you wish to convert into a contained database, you must make changes to the database properties and also address any instance-level dependencies that may be present:
ALTER DATABASE [YourDatabaseName] SET CONTAINMENT = PARTIAL;
GO
It’s recommended to use tools and scripts provided by Microsoft to identify and resolve any instance level dependencies before converting an existing database to a contained one.
Managing Contained Database Users
One of the key aspects of a contained database is the way it handles user authentication. Instead of relying on server-level logins, contained databases support the creation of database-level users that authenticate directly within the database:
CREATE USER [YourUsername] WITH PASSWORD = 'YourComplexPassword';
GO
Care should be taken that these credentials are managed securely and follow best practices for password complexity and user access control.
Best Practices and Considerations for Contained Databases
Adopting any new feature or methodology comes with its caveats, and contained databases are no different. Here are some essential best practices and considerations:
- Review Feature Support: Always check current SQL Server documentation to ensure that all necessary features are supported in contained databases for your version of SQL Server.
- Comprehensive Migration Plan: Outline a detailed migration plan which includes thorough testing in a non-production environment before migrating to a contained database in a live system.
- Audit and Monitor: More than ever, audit policies and monitoring are critical to maintaining the integrity and security of contained databases. Regular checks must be performed to identify and resolve any security or connectivity issues.
- Documentation: Clear documentation for the behavior of the contained database, along with differences from traditional databases, should be maintained for reference and troubleshooting purposes.
- Use of Partial containment as an Intermediate Step: If unsure, start with partial containment to balance the benefits with some initial fallback to instance-level configurations and move to full containment gradually as confidence builds.
Considering these best practices while deploying contained databases ensures a smoother transition and ultimately, a more stable and portable database environment.
Conclusion
Contained databases in SQL Server present a valuable paradigm for database administrators looking to enhance the mobility and resilience of their databases. When carefully planned and implemented, they can be a game-changer in effectively managing database environments and simplifying critical operations such as migrations and updates, while still providing a high degree of security and self-containment.
The road to adopting contained databases requires attention to detail and a clear understanding of the system’s requirements and limitations. By leveraging the insights and best practices discussed in this article, IT professionals can harness the full potential of contained databases to streamline processes and support the evolving needs of modern business applications.
FAQs about Contained Databases in SQL Server
What versions of SQL Server support contained databases?
The feature is available starting from SQL Server 2012. However, subsequent versions have continued to refine and support contained databases.
Can contained databases be used with SQL Server Always On Availability Groups?
Yes, contained databases are supported with Always On Availability Groups, enhancing their ease of failover and redundancy capabilities.
Do contained databases support both SQL and Windows Authentication?
Contained databases support both SQL Authentication and Windows Authentication, but authentication is specific to the database and not at the SQL Server instance level.
Is it possible to revert a contained database back to a traditional database?
Yes, it is possible to convert a contained database back to a non-contained one, although this may require resolving dependencies that were previously removed or handled within the contained database.
Does switching to a contained database model require downtime?
While the switch itself incurs minimal downtime, it is strongly advised to allot time for thorough testing before implementing a contained database in a production environment.
