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What Is Failover Clustering? How Does It Work + Solutions

Companies that need online transactions cannot afford server breakdowns. As a result, these businesses seek ways to create a failsafe procedure that keeps their data safe even if the server collapses. One such method is failover clustering. 

Failover clustering can be governed by managed domain name system (DNS) provider solutions; however, understanding its mechanism and key features can help limit any failover challenges.

This approach keeps your server workloads scalable and available. Many major server programs, such as Microsoft Exchange, Microsoft SQL Server, and  Hyper-V, rely on failover clustering to protect themselves. 

Some failover clusters employ physical servers, while others use virtual machines (VMs). Everyone selects the kind of cluster they need based on the requirements of their server application.

A cluster consists of two or more nodes that exchange data and software to be processed through physical cables or a specialized secure network. Clustering technology of several types can be used for load balancing, storage, and concurrent or parallel computing. In some instances, failover clusters are combined with extra clustering technologies.

A failover cluster’s primary function is to provide CA or HA for applications and services. CA clusters, also known as failure tolerant (FT) clusters, let end-users continue using applications and services even if a server fails. You might see a brief interruption in service caused by HA clusters, but the system can recover with no data loss and little downtime.

Why is failover clustering important?

With failover clustering, you can repair inactive nodes without shutting down your database, avoiding downtime concerns while quickly repairing broken servers. Furthermore, in the event of a hardware failure, this technique terminates the database to protect the active nodes.

Failover clustering also automates data recovery in the event of a failure. This reduces your reliance on the information technology (IT) crew and allows your servers to recover quickly. It also delivers excellent structured query language (SQL) cluster availability with minimal downtime. The automated failover functionality of failover clustering preserves the function of your database, even if there’s a hardware breakdown.

How do failover clusters work?

Failover clustering consists of two fundamental processes, HA and CA, for server applications. 

While CA failover clusters try to reach 100% availability, HA clusters strive for 99.999%, commonly known as five nines. This downtime totals no more than 5.26 minutes each year. CA clusters have higher availability but require more hardware to operate, increasing their overall cost.

High availability failover clusters

A high availability cluster is a collection of independent computers that share resources and data. A failover cluster’s nodes have access to shared storage. A monitoring link is also included in high-availability clusters to check the other servers’ heartbeat or health. A heartbeat is a private network shared only by the nodes in the cluster. It’s not accessible from the outside. 

At any point, at least one node in a cluster is active, and at least one is dormant or passive.

In a basic two-node arrangement, if Node 1 fails, Node 2 recognizes the failure via the heartbeat connection and configures itself as the active node. Clustering software on each node guarantees clients connect to an active node.

Larger installations may employ dedicated servers to administer the cluster. A cluster management server always sends heartbeat signals to identify any nodes failing and, if so, to tell another node to take up the work.

Some cluster management software tools handle HA for VMs by grouping the machines and servers into a cluster. If a host fails, a different host resumes the VMs.

As a possible single failure point, shared storage represents a risk. However, combining a redundant array of independent disks 6 and 10  – aka RAID 6 and RAID 10 – can help maintain service even if two hard drives fail.

Electrical power might be another single point of failure if all servers are connected to the same grid. Providing each node with its own uninterruptible power supply (UPS) keeps them protected.

Continuous availability failover clusters

Unlike the HA paradigm, a fault-tolerant cluster comprises numerous computers that share a single copy of a computer’s operating system (OS). Software commands given to one system are also executed on the other systems.

CA insists that the organization employs formatted computer equipment and a backup UPS. CA needs a constantly accessible and almost perfect replica of the physical or virtual system running the service. This redundancy model is known as 2N.

CA systems can compensate for a wide range of faults. A fault-tolerant system may identify a malfunction of:

  • A hard disk drive
  • A processing unit in a computer
  • A subsystem for input and output (I/O)
  • A power source
  • A component of a network

The failure point may be discovered promptly, and a backup component or method can take its place immediately without disrupting the next service.

Clustering software can connect two or more servers to behave as a single virtual server or construct various alternative CA failover cluster configurations. For instance, if one of the virtual servers fails, the others respond by temporarily removing the virtual server from the cluster quorum. The virtual server then redistributes the burden across the other servers until the crashed server is ready to restart.

A double hardware server with all physical components replicated is an alternative to CA failover clusters. They compute separately and concurrently on various hardware platforms and synchronize using a dedicated node that monitors the results from both physical servers. While this solution provides protection, it may be more expensive. 

Failover clustering features

Many organizations use failover clustering for mission-critical applications. This is because the following characteristics make failover clustering a significant technique.

  • Scalability: Because failover clustering is based on a group of clusters collaborating to prevent server failure, you can easily and readily scale as needed by adding new clusters. 
  • Stability: Clustered servers connect through wires. The remaining clusters can still offer service even if one or more fail due to external factors.
  • Real-time monitoring: The cluster nodes are constantly monitored to make sure they work properly. When a cluster gets restarted or transferred onto another node. 
  • Cluster shared volume (CSV): This feature provides a consistent and distributed namespace for nodes to use while working with shared storage. It’s crucial to keep server applications running without interruption from start to finish.

Types of failover clusters

Significant advancements in failover clustering have occurred in the last decade, with many organizations now offering their own version of clustering solutions. Some of the most common cluster services are detailed here.

VMware failover clusters

VMware provides numerous virtualization technologies for VM clusters. The vSphere vMotion’s CA architecture precisely duplicates a VMware virtual machine and its network between physical data center networks.

VMware vSphere HA, a second product, provides HA for VMs by grouping them and their hosts into a cluster for automated failover. Additionally, the program does not rely on external components such as DNS, which lowers possible points of failure.

Windows server failover cluster 

The Windows server failover cluster (WSFC) method fosters the creation of Hyper-V failover servers. Between 2016 and 2019, this strategy grew popular among Microsoft Windows users. WSFC allows cluster monitoring and offers the necessary failover mechanism automatically. In the event of a server loss, WFSC moves the clusters to a separate node or attempts to restart them. Additionally, its CSV technology provides a distributed namespace that allows several nodes to share memory.

SQL server 

This Microsoft product, introduced with SQL Server 2017, has robust HA solutions that use WSFC technology. SQL server components are considered WSFC cluster resources in this context. They’re further integrated with other WSFC-dependent resources. As a result, WSFC has authority over identifying and communicating orders to restart a SQL server instance or to move instances like those to a new node.

Red Hat Linux 

Other than Microsoft, other operating system vendors come with their own failover cluster solutions. For example, Red Hat Enterprise Linux (RHEL) fans can use the HA extension and Red Hat Global File System (GFS/GFS2) to establish HA failover clusters. Single-cluster stretch clusters spanning many locations and multi-site, disaster-tolerant clusters are supported. Storage area network (SAN) data storage replication is commonly used in multi-site clusters.

Applications of failover clustering

This robust mechanism facilitates the following real-time applications.

Availability of mission-critical applications.

Online transaction processing (OLTP) computers must have fault-resistant systems. OLTP, which requires complete availability, is used for airline reservation systems, electronic stock trading, and ATM banking.

Many industries, such as manufacturing, shipping, and retail, employ CA clusters or failure-resistant computers for mission-important applications. E-commerce, order management, and staff time clock systems count as examples.

High availability clusters are often acceptable for clustering applications and services that require only five-nines uptime.

Disaster relief

Disaster recovery also benefits from failover clustering. It is strongly recommended that failover servers be hosted at remote sites because a calamity such as a fire or flood destroys all physical hardware and software.

Storage Replica, a technology that duplicates volumes between servers for disaster recovery, is included in Windows Server 2016 and 2019. Stretch failover is a technology feature that lets failover clusters span two locations.

Organizations can replicate data over various centers by extending failover clusters. If tragedy strikes at one location, all data is preserved on failover servers at the others.

Replication of a database

According to Microsoft, the WSFC was first launched in Windows Server 2016 to safeguard “mission-critical” services, like its SQL server database and Microsoft Exchange communications server.

For database replication, other vendors supply failover cluster technology. For example, MySQL Cluster has a heartbeat method that enables fast failure detection to other nodes in the cluster, often in under a literal second, with no service disruptions to clients. 

Databases may be replicated to faraway sites using the geographic replication capability.

Benefits of failover clusters

The idea of failover clusters is to ensure that users experience minimum disruptions in service. However, other additional benefits of failover clustering are discussed below.

  • Increased resource availability: If one intelligent server fails, the others in the cluster pick up the burden. This saves crucial time and information.
  • Strategic resource allocation: You get to distribute projects between nodes in whatever way you choose. This minimizes overhead since not all computers are required to execute all projects simultaneously, giving you a way to use your resources more freely.
  • Increased processing power: More machines, more power.
  • Greater scalability: As your user base and report complexity expand, so can your resources.
  • Simplified management: Clustering makes handling significant or quick-changing systems easier.

Limitations of failover clustering

As significant as failover clustering is, it comes up against the following limitations.

  • Complex configurations: Failover clustering configuration for Windows requires you to handle many networks and network cards at once. As a result, deploying this method is difficult, especially for beginners.
  • Tool integrations: Windows failover clustering and Hyper-V must be more closely integrated. You have to adjust each of them to complete failover clustering successfully. 
  • Web interface: There’s no web interface to adjust cluster parameters. To access the cluster manager feature, you must manually log in to a remote desktop.

Failover clustering solutions: managed DNS providers

By working in conjunction with failover clustering systems, managed DNS providers redirect traffic to alternate servers or data centers during failover events, ensuring uninterrupted access to your services so you achieve high availability and minimize downtime.

Top five managed DNS providers:

* Above are the top five leading managed DNS providers software from G2’s Fall 2023 Grid® Report.

Click to chat with G2s Monty-AI

Modernizing reliability 

Failover clustering has emerged as a reliable and essential option for high availability and fault tolerance within current IT infrastructures. It provides ongoing operations despite hardware failures or scheduled maintenance by automatically spreading workloads and resources across numerous networked nodes. This technology gives you another way to handle the most important aspect of your business – making each customer’s experience safe and happy.

Fortifying your system’s resilience doesn’t hurt, either!

Get started with a guide to DNS security for a robust system strategy.