Clustering is a networking concept that involves linking two or more machines together — often called cluster nodes — and enabling them to function as a unified system. Applicable to both servers and computers, clustering focuses on tackling demanding workloads more easily by using a shared CPU, GPU, and memory pool. 

This computing approach is useful for connecting machines over a local area network (LAN) or wide area network (WAN). Such clusters can switch quite effectively between tasks, yet each machine maintains its own OS. While it's recommended that each node runs the same OS to simplify task delegation, it's possible (yet more challenging) to establish clusters running multiple OSes. Depending on setup, clustering often leverages machines spread across geographical locations. 

Clustering has been a mainstay in the networking realm since the 1960s. Originally designed for distributed systems and shared data storage, clustering introduced major performance benefits across single-CPU nodes. However, the rise of multi-processor machines meant that organizations across industries could tackle even more complex tasks with public-facing benefits — such as climate modeling, medical diagnostics, AI/ML, mutli-cloud computing, and load balancing. This is referred to as high-performance computing (HPC).

How does clustering work?

Clustering enables horizontal scaling for improved performance and stability. Instead of assigning tasks to one machine and swapping hardware components to add processing power, organizations can connect multiple machines for increased scalability and reliability. This can also be more cost-effective, since clustering supports such a wide variety of hardware setups instead of requiring top-flight components to work effectively. 

Clustering can also fit into a SD-WAN strategy, both to increase the performance/reliability of the SD-WAN network and to configure the SD-WAN to cluster other services. Networks of connected computing nodes typically need a software component at their core, such as a control plane, to maintain visibility and enable streamlined management. Not only can this help optimize performance across all nodes, but it also supports high availability through health checking and related mechanisms. 

Clustering relies on the following components: 

  • Computing nodes – Servers or computers that can run distributed workloads using CPU, GPU, and memory resources

  • Primary or leader nodes – Servers or computers that help assign tasks across other healthy and available nodes, while helping them work together effectively

  • Load balancers – Intermediary devices that can route application traffic intelligently between cluster nodes, ensuring better performance, security, and scalability across the entire system

  • Health checking or heartbeat monitoring – A mechanism that continuously monitors nodes within the greater cluster, ensuring that all nodes are functional while alerting the primary node if another goes offline. This allows workloads to be rerouted to working machines.

In most clustering implementations, homogeneity is advantageous — where resources, operating systems, and configurations are shared by every connected node. However, heterogeneous implementations with nodes that use separate resource pools and OSes are feasible. These setups are harder to establish and maintain, but do offer extra flexibility. 

Not every cluster is built for the same purpose. While load balancing is a core use case for clustering, high availability clusters help maintain another layer of failover protection while enabling functions supported by VRRP.

What are the benefits of clustering?

Organizations may choose to implement clustering for the following reasons: 

  • Clustering enables horizontal scalability and thus helps teams run more complex tasks concurrently — without having to work around the limitations of any one machine. 

  • Clustering helps boost performance by making the most efficient use of available resources, through functions such as load balancing and centralized management. 

  • Clustering is often cheaper to set up vs. other load management setups. 

  • Clustering adds reliability to mission-critical systems and helps teams keep tabs on which nodes are working and which aren't. It also allows for rapid traffic switching when failures strike.

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Does HAProxy support clustering?

Yes! HAProxy One provides functions critical to clustering such as load balancing, high availability, and scalability. Situated between your applications and backend servers, HAProxy One lets you distribute traffic intelligently between nodes to prevent slowdowns and crashes while providing protection against a broad spectrum of threats. HAProxy also supports VRRP-supported active/active or active/passive clustering to help remove failed nodes from circulation — automatically promoting working nodes to keep tasks running smoothly. 

To learn more about HAProxy and clustering, check out our high availability solution or our active/active clustering documentation.