MCSA Certification Series: All You Need to Know about Failover Clustering
Windows Server has several features that allow it to function seamlessly and ensure that applications and features are available throughout the life cycle. The Failover Cluster is one such feature; working as both a fault-prevention measure and a high app and feature delivery system. It also delivers new and better features for datacenter customers who are software-centric, manages several other workloads while maintaining clusters in both virtual machines and physical hardware.
As part of our MCSA certification tutorial series, in this article, we will be talking about what failover clustering is, how it works, and its benefits.
Defining Failover Cluster
Windows Server, by default, provides administrators the capability of connecting several servers into one server cluster. On the basic level, the cluster consists of an independent group of computers that combine their functionality, in order to increase the scalability and availability of clustered applications and services (now defined as cluster roles).
Each of the independent machines that make up the servers which then form the cluster, are connected wither by cables or software. Individual servers within the clusters are called nodes, which makes them separate entities operating within the same group/system. This creates a fail-safe, in the way that if one of the nodes encounters an issue, the others continue providing service. This fail-safe system is known as ‘failover’.
To make sure that the remaining clusters are working at their best, and clustered roles are being fulfilled, the latter are monitored actively. If there is an issue with the clustered roles, they are either transferred on to another node within the cluster, or they are restarted to ensure maximum functionality.
Failover Cluster Functionality Requirements
A failover cluster has the following requirements, which must be fulfilled to construct the network cluster and continue cluster roles without fault or stoppage:
- The hardware specifications of each server must be the same. This means processing power, memory and software units must be uniform.
- Storage space must be shared between the servers in the cluster. This is to ensure that the data stored on one server/node can be accessed by another, in the event of an issue.
The servers communicate via a series of signals, called ‘heartbeats’, on a dedicated network. If the signals, or heartbeats have been initiated by the server that is active, and relayed to the standby signal with very specific intervals, they will be called push heartbeats. In case the active server does not send a push heartbeat to the standby server for a certain amount of time, the latter takes over the responsibilities of the active server and is defined as such from there on.
If a communication signal is sent from the standby server to the active server, it will be known as a pull heartbeat. In case the standby server sends a pull heartbeat and the active server does not respond to it within the set time limit, the former will, once again, take over the responsibilities of the latter, assuming that the active server has failed.
Cluster Shared Volume (CSV)
When servers are configured in a failover cluster, they provide a functionality known as Cluster Shared Volume. This functionality provides a constant distributed namespace, that can be used by the clustered roles to gain access to the storage space that has been shared across all the nodes. With this added element, users will experience minimal disruptions in the delivery of service; through Failover Clustering.
Practical Applications of Failover Clustering
Following are some areas where failover clustering can be applied:
- Shared storage space for applications such as Hyper-V virtual machines and Microsoft SQL Server. Because of the nature of clustering, the storage is highly accessible and continuously available.
- Highly available clustered applications and services which can run on virtual machines and/or physical servers that run Hyper-V.
Knowing the fundamentals of failover clustering and related features of Windows Server can be tremendously beneficial for both potential networking engineers and those seeking an MCSA certification. Additionally, since each new edition of MS Server presents new features and functionalities, an MCSA certification now will assist in easily coming to grips with all the present and future offerings of Microsoft Server.