SQL Server Failover Cluster Instances

What are SQL Server Failover Cluster Instances?

SQL Server Failover Cluster Instances are a solution for providing high availability and disaster recovery for the SQL Server Database Engine. In brief, when one node in a cluster fails or needs to be taken offline for maintenance, the SQL Server instance fails over to another node within the same cluster almost seamlessly, keeping the application up and running for end-users with little to no impact on service.

To set up a SQL Server Failover Cluster Instance (FCI), at least two servers are required to form the Windows Server Failover Cluster (WSFC). The servers in the cluster must meet specific requirements, including a consistent hardware configuration and high-speed network connectivity between nodes, typically having similar specifications or hosted in the same datacenter or availability zone.

Once you have two or more servers set up, you will start installing SQL Server. When installing SQL Server, you will choose the “Failover Cluster Instance” option from the installation wizard rather than a standalone installation. This will install the SQL server binaries onto all nodes of the cluster, and create a virtual “cluster resource” associated with the SQL Server instance.

After installation, the SQL Server failover clustering feature is enabled by adding SQL Server instance(s) as a clustered resource. The process of creating clustered resources involves assigning disk drives, IP addresses, network name, and SQL Server properties, such as SQL Server Network Name, IP address, and instance name. For example, to create SQL Server 2019 FCI, you would install SQL Server on computers that will be part of the failover cluster, specify the clustered SQL Server instance name (SQL2019FCI) to associate with the virtual cluster resource, and the SQL Server network name (SQL2019FCI.mydomain.com) to be registered with Domain Name System (DNS).

While failover clustering provides high-availability and automatic failover, split-second automatic failover isn’t always possible. One such scenario is when a network connectivity issue is detected but the SQL Server is still responsive. To overcome the limitations of automatic failover, Microsoft introduced the concept of a “forced failover” or “manual failover” that can be initiated to manually move the SQL Server to another node in the cluster. Using the Failover Cluster Manager, a SQL Server administrator can initiate the failover of an SQL Server instance to another node in the cluster, either for maintenance purposes or in case of an emergency.

Why use SQL Server Failover Cluster Instances?

SQL Server Failover Cluster Instances provide high availability and disaster recovery capabilities for mission-critical SQL Server workloads.

By using SQL Server FCIs, you can ensure that your SQL Server instances are always up and running, even when unexpected hardware, software or network issues arise. This helps to minimize application downtime, ensure data is always available, and provide a seamless experience for end-users who rely on the application.

In addition to high availability, SQL Server Failover Cluster Instances also provide scalability benefits. By leveraging the power of multiple nodes in a cluster, you can scale SQL Server workloads as needed to meet growing demands.

For example, consider a high-traffic e-commerce website with a SQL Server database that stores all product data and orders. During peak holiday shopping periods, the site experiences higher-than-usual traffic, causing the SQL Server instance to run slow or even crash. By implementing a SQL Server FCI, the database can be divided across two or more servers, enabling the workload to be spread across the servers to ensure application performance is maintained under high load.

Another benefit of SQL Server FCIs is simplified management. By running multiple instances of SQL Server on a single cluster, databases can be easily managed, and backup, restore, and other maintenance operations can be performed more efficiently.

However, there are some considerations when using SQL Server FCIs. For instance, not all features of SQL Server are supported in a failover clustering environment, including Excel Services, Reporting Services, and the Visual Studio tools. Additionally, failover clustering requires significant planning, testing, and documentation to ensure the cluster is properly configured and maintained over time.

How to Configure SQL Server Failover Cluster Instances

Configuring SQL Server Failover Cluster Instances requires a series of steps to ensure the cluster is properly configured and operational.

The first step is to ensure that the servers meet the requirements for failover clustering. This includes ensuring the servers have the same hardware specifications, such as CPU, memory, and storage, and ensuring there is high-speed network connectivity between nodes.

Next, you’ll need to install Windows Server Failover Clustering (WSFC) on the servers that will be part of the cluster. Once WSFC is installed, you’ll need to create a new failover cluster and add the servers to the cluster. You can use the Windows Failover Cluster Manager to create the new cluster and add nodes to the cluster.

After creating the cluster and adding nodes to it, you can install SQL Server on each server in the cluster. When installing SQL Server, choose the “Failover Cluster Instance” option to set up the SQL Server Failover Cluster Instances. This installs the SQL Server binaries onto all nodes of the cluster and creates a virtual “cluster resource” associated with the SQL Server instance.

Once SQL Server is installed, the next step is to configure the SQL Server instance to be added to the Windows Failover Cluster. This involves assigning disk drives, IP addresses, network name, and SQL Server properties, such as SQL Server Network Name, IP address, and instance name. You can use the SQL Server Configuration Manager to add or remove SQL Server instances as a clustered resource.

After configuring the SQL Server instance, test the failover by simulating a node or SQL Server instance failure. You should also test the failback to ensure that the cluster can handle a failover and failback event.

In addition, be aware of performance considerations when configuring SQL Server Failover Cluster Instances. Testing can help identify areas that need optimization. A best practice is also to monitor the SQL Server and cluster performance, alert logs, and setup automated management jobs.

Overall, while the configuration of SQL Server Failover Cluster Instances requires several steps, following the process can ensure that the application is available at all times, even during unexpected events.

Managing Failover Cluster Instances in SQL Server

Managing SQL Server Failover Cluster Instances involves performing ongoing maintenance tasks to ensure that the cluster is healthy and able to withstand any failures.

One important task is to monitor the cluster for events such as resource failures or changes in resource state. You can monitor the cluster using the Failover Cluster Manager or by creating custom scripts to monitor the cluster status. For example, you can set up alerts to be triggered when a resource fails, logs when a resource is offline, or emails to notify administrators of the failure.

Another critical task is to backup and restore the SQL Server database. Backing up the database ensures there is a copy of the data in case of a server failure, while restoring the database recovers the database to the same state as a previous point in time.

When performing backup and restore tasks, you must take into consideration that SQL Server Failover Cluster Instances are not a shared storage solution and each node has its own backup and restore strategy. The backup should be performed on each node and should include system databases, user databases, and full-text catalogs.

To streamline backup and restore tasks, you can use the SQL Server Management Studio (SSMS) to schedule backup and restore jobs or setup alerts. SSMS provides a graphical interface to monitor the status of these jobs and receive notifications if they fail.

Lastly, you need to be prepared to handle failover events. While failover is designed to happen automatically, sometimes manual failover may be required. For example, when performing maintenance on one of the nodes, you may want to manually fail over the instance to the other node prior to the maintenance event.

To initiate a manual failover, you can use the Failover Cluster Manager or use the cluster command-line interface (CLI). It’s important to test the manual failover to ensure the process runs smoothly and the application recovers with minimal downtime.

In summary, managing SQL Server Failover Cluster Instances involves monitoring the cluster, performing backups and restores, and being prepared to handle failover events. By following best practices and performing regular maintenance tasks, you can ensure that your SQL Server instances remain highly available and ready to withstand any unexpected failures.

Summary

Overall, by following best practices and regularly maintaining your SQL Server Failover Cluster Instances, you can ensure that your application is highly available, providing the best user experience with minimal downtime.