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Nodes and Clusters: The Building Blocks of High Availability

March 4, 2025 by Jason Aw Leave a Comment

Updating LifeKeeper for Linux A Checklist for Success

Nodes and Clusters: The Building Blocks of High Availability

I wanted to spend some time reviewing the terms “nodes” and “clusters.” For the purposes of this blog, I will explain how SIOS uses these terms and others and what they specifically mean.

These might be considered standard terms in the world of distributed computing, but if you are new to the field, you may wonder exactly what they mean.

What Are Nodes in Distributed Computing?

When I started with SIOS, I noticed that the terms node and cluster were common, everyday words that you would hear many times daily. I kept asking myself, ‘Why are they using the word “node”’? It sounds from the context that they mean server, but why do they say node? To explain, a node can be a server, but it can also be a client computer or a peer; it is essentially any component used to perform computing duties and route traffic.

In Amazon Web Services (AWS), a node can be a virtual machine implemented as an EC2 instance. You can install and run software on it, and it can have a network interface that can be used to communicate with it and for it to connect to other nodes. When you SSH into an AWS EC2 instance, the client computer from which you are launching your SSH session is an example of a client node, and you are connecting to an EC2 server instance node. Nodes can be a physical machine on-premises or a virtual machine (VM).

Understanding Clusters: How Nodes Work Together

Let’s move on to the term “cluster”. This word might make one think of things that are stuck together. In the distributed computing world, this means nodes that are linked together to form a combined resource that might handle a bigger task than a single node can handle. At SIOS, we have special cluster protection software on each node that monitors the volumes and can launch failover operations when problems are detected or respond to resources being intentionally taken in and out of service by a user.

You might link nodes together in a cluster to perform automatic backups. You could run a database server on a separate node to isolate the computing power/disk I/O and the data from other operations.

The Role of Redundancy in High-Availability Clusters

Clusters can also provide redundancy to allow services to remain up when one node fails. Redundancy of operation is not a new concept. The days of running any vital operation on a single server that has no redundancy are hopefully well behind us.

For example, in the blade-computing world, redundancy is facilitated in a blade server configuration by running two computing modules within the same unit. The server firmware handles the failover/switchover logic. Power supplies, and rack KVM, are shared amongst the load of server hardware for cost savings.

Facility operators may add more hardware to a server in an incremental fashion to handle extra load. This allows an operator to right-size their system and purchase / build it using standardized components from the rack manufacturer. This provides a more limited but similar scaling mechanism to that in the cloud world,  the difference being that it is all hosted in one box. On-premises rack hardware such as this or similar can be used to construct clustered nodes.

Cloud-Based Clusters vs. On-Premises Clusters

Cloud clusters benefit from all of the attributes of redundancy built into rack server equipment, as they are basically discrete VMs that run on shared data-center hardware owned by the cloud provider. However, they permit the customer to spread their clusters over different locations, intentionally load-slicing their computer needs into VM’s running in different physical buildings in other areas of the cloud provider’s physical data centers.

This provides an enormous resiliency to single-site outages. A cluster implemented in the cloud utilizing servers in various locations can tolerate complete power loss to one location.

Nodes and Clusters Explained

Some questions that come up:

Q. Is a cluster the same as a node?

A. No, a node is typically one component that can perform computer duties. A cluster consists of 2 or more nodes.

Q. What is a 3-node cluster?

A. A 3-node cluster is a cluster of 3 nodes with communication paths between each of the respective nodes. 3 nodes, being an odd-numbered configuration, typically one of the nodes will be a so-called ‘witness’ node and may not perform other work. In the event of a partially failed network, and a node being unable to communicate with its peer, the two main server nodes may not be able to determine who should take control (this phenomenon is called ‘split-brain’). A witness node can offer information on what nodes it can see are in service,  providing data to resolve the split-brain to bring up one active node and put the other node into standby mode, regaining correct control of the nodes.

Q. What is 2 node cluster?

A. A 2 node cluster is a cluster of 2 nodes with one or more communication paths between them. This is typically used to run services on a primary node and have the second node on standby.

Q. How many nodes make a cluster?

A. 2 or more nodes make a cluster.

Maximizing High Availability with Nodes and Clusters

In summary, clusters are formed from nodes; a node is an independent computing module with networking capabilities. Be aware of the benefits of putting your nodes in different physical locations to guard against downtime in one area.

Contact SIOS today to learn how our clustering solutions can help you optimize high availability and minimize downtime.


Author: Paul Scrutton
Principal Software Engineer at SIOS

Reproduced with permission from SIOS

Filed Under: Clustering Simplified Tagged With: High Availability

Achieving High Availability for SAP HANA

February 14, 2025 by Jason Aw Leave a Comment

Achieving High Availability for SAP HANA

Achieving High Availability for SAP HANA

Countless businesses rely on SAP ERP systems for their mission-critical, high availability applications. However, with the 2027 deadline for transforming these systems to the new HANA environment looming, it’s vital that these enterprises consider how they will achieve high availability under the new regime – ideally, before they’re faced with unplanned downtime.

It’s vital that businesses start thinking about this change early, as achieving the top-tier “five nines” standard of high availability – 99.999% uptime – under the HAHA environment comes with many challenges. Fortunately, these can be overcome with well-designed architecture and the right technical expertise.

This Database Trends & Applications article written by Ian Allton, Solutions Architect at SIOS Technology Corp published in their Big Data Quarterly looks to help enterprises make the right start in their transition to HANA by running through the three steps to achieving best practices for high availability with an SAP HANA database.

Reproduced with permission from SIOS

Filed Under: Clustering Simplified Tagged With: High Availability, high availability - SAP

Establishing a Software-Based, High-Availability Failover Strategy for Disaster Mitigation and Recovery

February 4, 2025 by Jason Aw Leave a Comment

Establishing a Software-Based, High-Availability Failover Strategy for Disaster Mitigation and Recovery

Establishing a Software-Based, High-Availability Failover Strategy for Disaster Mitigation and Recovery

Cloud outages happen—don’t let them disrupt your operations. In Disaster Recovery Journal, Dave Bermingham shares how SANless clustering ensures seamless failover across multi-cloud environments, delivering flexibility, efficiency, and uninterrupted service.
Reproduced with permission from SIOS

Filed Under: Clustering Simplified Tagged With: disaster recovery, High Availability

Configuring SQL Server Standard Edition for High Availability on AWS

January 13, 2025 by Jason Aw Leave a Comment

Configuring SQL Server Standard Edition for High Availability on AWS

Configuring SQL Server Standard Edition for High Availability on AWS

It’s not always clear how to build a high availability (HA) SQL Server infrastructure on AWS. After all, there are two different paths leading to a SQL Server deployment on AWS. One involves the Amazon Relational Database Service (Amazon RDS); the other involves Amazon Elastic Compute Cloud (Amazon EC2). Either one can be configured across multiple Availability Zones—essentially, separate data centers—to ensure that there’s no single point of data center vulnerability.

Amazon RDS: Simplicity in High Availability Deployment

Amazon RDS is a fully managed service; you only need to tell AWS that you want a multi-center instance of SQL Server. AWS will set it up for you, and you’re off and running.

Amazon EC2: Flexibility and Control for SQL Server

With Amazon EC2, though, you will need to do most of the work setting up and maintaining your infrastructure. AWS will deploy and support the underlying virtual machine (VM) that you’ve chosen, and AWS will ensure that the operating system is properly configured and updated, but on Amazon EC2, you’re in control from there on out.

Choosing Between Amazon RDS and EC2 for SQL Server HA

Amazon RDS makes it easy; Amazon EC2 gives you flexibility and control. Which environment you choose for a HA deployment of SQL Server standard edition really depends on the number of databases you’re going to use, the release of SQL Server you plan to use, and the level of availability you want to ensure.
This article in The New Stack by SIOS’ Senior Technical Evangelist Dave Bermingham examines the trade-offs encountered when considering whether to use Amazon RDS or Amazon EC2. It considers release levels, the limits of replicating databases using native SQL Server replication tools, and the differences between the availability SLAs associated with Amazon RDS and Amazon EC2.

Optimize Your SQL Server HA Strategy with SIOS

Ensure continuous uptime and data protection with the right high availability solution for your SQL Server Standard Edition on AWS. Contact SIOS today to learn how our expertise can help you achieve your HA goals with confidence.

Reproduce with permission from SIOS

Filed Under: Clustering Simplified Tagged With: Amazon AWS, High Availability

SIOS Technology Expands Support in Linux Product Release

January 9, 2025 by Jason Aw Leave a Comment

SIOS Technology Expands Support in Linux Product Release

SIOS Technology Expands Support in Linux Product Release

We’re excited to announce expanded support for the SIOS LifeKeeper for Linux 9.9.0 release, including:

  • SAP HANA 2.0 on RHEL 9.4
  • SAP on RHEL 9.4
  • Watchdog support on RHEL 9
  • FUJITSU Software Enterprise Postgres 16 SP1

These newly supported configurations are fully compatible with our Linux product’s current general availability version and will continue to be supported in future releases. Importantly, no software update is required to take advantage of these additions.

Stay tuned for more updates as we continue to enhance our solutions to meet your high availability and disaster recovery needs.

Reproduced with permission from SIOS

Filed Under: News and Events Tagged With: disaster recovery, High Availability, Linux, SIOS LifeKeeper

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