| title | description | author | ms.author | ms.date | ms.service | ms.subservice | ms.topic |
|---|---|---|---|---|---|---|---|
Support for High Availability, Disaster Recovery for the Microsoft Drivers for PHP for SQL Server |
Support for High Availability, Disaster Recovery for the Microsoft Drivers for PHP for SQL Server |
David-Engel |
davidengel |
07/31/2018 |
sql |
connectivity |
conceptual |
[!INCLUDEDriver_PHP_Download]
This topic discusses [!INCLUDEssDriverPHP] support (added in version 3.0) for high-availability, disaster recovery.
Starting with version 3.0 of the Microsoft Drivers for PHP for SQL Server, you can specify the availability group listener of a high-availability, disaster-recovery availability group or a failover cluster instance as the server in the connection string.
The MultiSubnetFailover connection property indicates that the application is being deployed in an availability group or Failover Cluster Instance and that the driver will try to connect to the database on the primary SQL Server instance by trying to connect to all the IP addresses. Always specify MultiSubnetFailover=True when connecting to a SQL Server availability group listener or SQL Server Failover Cluster Instance. If the application is connected to an Always On database that fails over, the original connection is broken and the application must open a new connection to continue working after the failover.
Full details on Always On availability groups can be found at the High Availability, Disaster Recovery Docs page.
Transparent Network IP Resolution (TNIR) is a revision of the existing MultiSubnetFailover feature. It affects the connection sequence of the driver when the first resolved IP of the hostname does not respond and there are multiple IPs associated with the hostname. The corresponding connection option is TransparentNetworkIPResolution. Together with MultiSubnetFailover it provides the following four connection sequences:
- TNIR Enabled & MultiSubnetFailover Disabled: One IP is attempted, followed by all IPs in parallel
- TNIR Enabled & MultiSubnetFailover Enabled: All IPs are attempted in parallel
- TNIR Disabled & MultiSubnetFailover Disabled: All IPs are attempted one after another
- TNIR Disabled & MultiSubnetFailover Enabled: All IPs are attempted in parallel
TNIR is enabled by default, and MultiSubnetFailover is Disabled by default.
This is an example of enabling both TNIR and MultiSubnetFailover using the PDO_SQLSRV driver:
<?php
$serverName = "yourservername";
$username = "yourusername";
$password = "yourpassword";
$connectionString = "sqlsrv:Server=$serverName; TransparentNetworkIPResolution=Enabled; MultiSubnetFailover=yes";
try {
$conn = new PDO($connectionString, $username, $password, array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION));
// your code
// more of your code
// when done, close the connection
unset($conn);
} catch(PDOException $e) {
print_r($e->errorInfo);
}
?>
A connection error will occur if the MultiSubnetFailover and Failover_Partner connection keywords are present in the connection string. An error will also occur if MultiSubnetFailover is used and the SQL Server returns a failover partner response indicating it is part of a database mirroring pair.
When upgrading a PHP application that currently uses database mirroring to a multi-subnet scenario, remove the Failover_Partner connection property and replace it with MultiSubnetFailover set to True and replace the server name in the connection string with an availability group listener. If a connection string uses Failover_Partner and MultiSubnetFailover=true, the driver will generate an error. However, if a connection string uses Failover_Partner and MultiSubnetFailover=false (or ApplicationIntent=ReadWrite), the application will use database mirroring.
The driver will return an error if database mirroring is used on the primary database in the AG, and if MultiSubnetFailover=true is used in the connection string that connects to a primary database instead of to an availability group listener.