What is failover clustering?
Consider the following scenario. We are on our college’s fee submission portal, submitting our fee at the last minute. There is a server from the bank’s side that is handling our requests in the background. What would happen if that server faces a technical issue and goes down? Will our session terminate, leaving us with a missed fee submission deadline? The answer is yes if the streaming service did not use failover clustering.
What is a failover cluster?
In a failover cluster, several server machines, also known as nodes, work together seamlessly to make applications and services prone to hardware failures and to accommodate surges in demand. So if a node in a failover cluster falters, another node can take its place, ensuring that the users of the application or service do not face significant service downtimes.
There are two primary types of failover clusters:
High-availability (HA) failover clusters
In high-availability (HA) clusters, all the nodes share a single storage database. Furthermore, all the servers are interlinked with
In case of a failure of the active node, the passive node will stop receiving the heartbeat signals and take over the connection as the active node. HA clusters ensure 99.999% (five nines) availability of connection. According to these statistics, 1 out of every 1,000 people using the service can face downtime or, if put in context to our example above, a missed transaction. We certainly do not want that. Let’s explore the second type of failover clusters.
Continuous-availability (CA) failover clusters
The five-nines availability of HA failover clusters will suffice for most use cases. However, we should take a more robust clustering approach for more critical applications like online banking, online order management, and stock trading, i.e., continuous-availability (CA) failover clusters.
In a CA cluster, all the nodes share a single copy of the OS, and all physical components are duplicated. Each node performs all the required functionality on its own and synchronizes with the other nodes. In case of a failure, the functional node instantly takes over as the active node.
Use cases of failover clustering
Failover clustering proves beneficial in several scenarios:
Mission-critical tasks: These include industrial applications like ATM banking, online transactions, and airline scheduling.
Database replication: Databases containing important data can be replicated onto different machines to ensure a failure of one storage element does not translate to a permanent data loss. Cloud storage servers may utilize this technology.
Disaster management: If nodes at a considerable distance constitute a failover cluster for an application or a service, a calamity striking at one location will not result in the entire service or application’s loss of functionality or data.
Available implementation options
VMware Failover Cluster: VMware offers virtualization options for failover clustering. During failures, virtual machine (VM) clusters made with VMware seamlessly migrate to healthy nodes. It is ideal for virtualized infrastructures and offers both HA and CA clustering.
Windows Server Failover Cluster (WSFC): Offered by Microsoft, WSFC is a native option for Windows users to implement failover clustering. WSFC offers both HA and CA clustering, making it a suitable choice for organizations utilizing Windows environments.
SQL Server Failover Cluster: SQL Server is also provided by Microsoft. It implements HA failover clustering for databases.
Red Hat Linux Failover Cluster: Red Hat Enterprise Linux (RHEL) offers failover cluster tools for Linux-based environments. It also supports clusters that span multiple sites for disaster-tolerant failover clustering.
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