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Make your database portable by using contained databases

  • Makale

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics

Use contained database users to authenticate SQL Server and Azure SQL Database connections at the database level. A contained database is a database that's isolated from other databases and from the instance of SQL Server or SQL Database (and the master database) that hosts the database.

SQL Server supports contained database users for both Windows and SQL Server authentication. When you're using SQL Database, combine contained database users with database-level firewall rules.

This article reviews the benefits of using the contained database model compared to the traditional login/user model and Windows or server-level firewall rules. Specific scenarios, manageability, or application business logic might still require use of the traditional login/user model and server-level firewall rules.

Traditional login and user model

In the traditional connection model, Windows users or members of Windows groups connect to the Database Engine by providing user or group credentials authenticated by Windows. Or users can provide both a name and password and connect by using SQL Server authentication. In both cases, the master database must have a login that matches the connecting credentials.

After the Database Engine confirms the Windows authentication credentials or authenticates the SQL Server authentication credentials, the connection typically attempts to connect to a user database. To connect to a user database, the login must be mapped to (that is, associated with) a database user in the user database. The connection string might also specify connecting to a specific database, which is optional in SQL Server but required in SQL Database.

The important principle is that both the login (in the master database) and the user (in the user database) must exist and be related to each other. The connection to the user database has a dependency upon the login in the master database. This dependency limits the ability of the database to be moved to a different hosting SQL Server instance or Azure SQL Database server.

If a connection to the master database is not available (for example, a failover is in progress), the overall connection time will increase, or the connection might time out. An unavailable connection might reduce connection scalability.

Contained database user model

In the contained database user model, the login in the master database is not present. Instead, the authentication process occurs at the user database. The database user in the user database doesn't have an associated login in the master database.

The contained database user model supports both Windows authentication and SQL Server authentication. You can use it in both SQL Server and SQL Database.

To connect as a contained database user, the connection string must always contain a parameter for the user database. The Database Engine uses this parameter to know which database is responsible for managing the authentication process.

The activity of the contained database user is limited to the authenticating database. The database user account must be independently created in each database that the user needs. To change databases, SQL Database users must create a new connection. Contained database users in SQL Server can change databases if an identical user is present in another database.

In Azure, SQL Database and Azure Synapse Analytics support identities from Microsoft Entra ID (formerly Azure Active Directory) as contained database users. SQL Database supports contained database users who use SQL Server authentication, but Azure Synapse Analytics doesn't. For more information, see Connect to SQL Database by using Microsoft Entra authentication.

When you're using Microsoft Entra authentication, users can make connections from SQL Server Management Studio by using Microsoft Entra universal authentication. Administrators can configure universal authentication to require multifactor authentication, which verifies identity by using a phone call, text message, smart card with PIN, or mobile app notification. For more information, see Using Microsoft Entra multifactor authentication.

For SQL Database and Azure Synapse Analytics, the database name is always required in the connection string. So you don't need to change the connection string when you're switching from the traditional model to the contained database user model. For SQL Server connections, the name of the database must be added to the connection string, if it's not already present.

Important

When you're using the traditional model, the server-level roles and server-level permissions can limit access to all databases. When you're using the contained database model, database owners and database users who have the ALTER ANY USER permission can grant access to the database. This permission reduces the access control of highly privileged server logins and expands the access control to include highly privileged database users.

Firewalls

SQL Server

For SQL Server, Windows Firewall rules apply to all connections and have the same effects on logins (traditional model connections) and contained database users. For more information about Windows Firewall, see Configure Windows Firewall for Database Engine access.

SQL Database firewalls

SQL Database allows separate firewall rules for server-level connections (logins) and for database-level connections (contained database users). When SQL Database connects to a user database, it first checks database firewall rules. If there's no rule that allows access to the database, SQL Database checks the server-level firewall rules. Checking server-level firewall rules requires access to the SQL Database server's master database.

Database-level firewall rules, combined with contained database users, can eliminate the need to access the master database of the server during the connection. The result is improved connection scalability.

For more information about SQL Database firewall rules, see the following topics:

Syntax differences

Traditional model Contained database user model
When you're connected to the master database:

CREATE LOGIN login_name WITH PASSWORD = 'strong_password';

Then, when you're connected to a user database:

CREATE USER 'user_name' FOR LOGIN 'login_name';		 When you're connected to a user database:

CREATE USER user_name WITH PASSWORD = 'strong_password';
Traditional model Contained database user model
To change a password in the context of the master database:

ALTER LOGIN login_name WITH PASSWORD = 'strong_password';		 To change a password in the context of the user database:

ALTER USER user_name WITH PASSWORD = 'strong_password';

SQL Managed Instance

Azure SQL Managed Instance behaves like SQL Server on-premises in the context of contained databases. Be sure to change the context of your database from the master database to the user database when you're creating your contained user. Additionally, there should be no active connections to the user database when you're setting the containment option. Use the following code as a guide.

Warning

The following sample script uses a kill statement to close all user processes on the database. Make sure that you understand the consequences of this script and that it fits your business before running it. Also make sure that no other connections are active on your SQL Managed Instance database, because the script will disrupt other processes that are running on the database.

USE master;

SELECT * FROM sys.dm_exec_sessions
WHERE database_id  = db_id('Test')

DECLARE @kill_string varchar(8000) = '';
SELECT @kill_string = @kill_string + 'KILL ' + str(session_id) + '; '  
FROM sys.dm_exec_sessions
WHERE database_id  = db_id('Test') and is_user_process = 1;

EXEC(@kill_string);
GO

sp_configure 'contained database authentication', 1;  
GO
 
RECONFIGURE;  
GO 

SELECT * FROM sys.dm_exec_sessions
WHERE database_id  = db_id('Test')

ALTER DATABASE Test
SET containment=partial

USE Test;  
GO 

CREATE USER Carlo  
WITH PASSWORD='Enterpwdhere*'  

SELECT containment_desc FROM sys.databases
WHERE name='Test'

Remarks

  • Contained database users must be enabled for each instance of SQL Server. For more information, see Contained database authentication (server configuration option).
  • Contained database users and logins with non-overlapping names can coexist in your applications.
  • Assume that a login in the master database has the name name1. If you create a contained database user named name1, when a database name is provided in the connection string, the context of the database user will be chosen over the login context for connecting to the database. That is, the contained database user takes precedence over logins that have the same name.
  • In SQL Database, the name of contained database user can't be the same as the name of the server admin account.
  • The SQL Database server admin account can never be a contained database user. The server admin has sufficient permissions to create and manage contained database users. The server admin can grant permissions to contained database users on user databases.
  • Because contained database users are database-level principals, you need to create contained database users in every database where you would use them. The identity is confined to the database. The identity is independent (in all aspects) from a user who has the same name and the same password in another database in the same server.
  • Use the same strength of passwords that you would normally use for logins.

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