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Cluster Topology: What is a Head Node?

March 2, 2021
15 min read
blog-what-is-a-head-node.jpg

The Importance of a Cluster Head Node

When working with a cluster there are a lot of operating pieces: switches, storage, compute nodes, applications, file systems, workloads, and more. The impact of unmanaged servers, storage, appliances and interactive sessions can lead to significant concerns, especially when it pertains to multiple users all competing eagerly for resources. Eventually user requests would outweigh the available resources and the results would be catastrophic! That's where the head node comes into play!

What is a Head Node?

In simple terms a head node, sometimes identified as a login node, is a configured system that sits in a Rack as part of a cluster and act as a Master node for the whole cluster in which case it becomes the single point for managing all the computational resources. It provides such things as management and scheduling services to the cluster;  it is considered to be one of the most important parts of a cluster and is essential to getting work done.

head-node-rack.png

In a cluster the head node provides services both internally and externally and, along with storage arrays and multiple compute nodes, as the name might suggest the head node is responsible for managing all of the resources within its control. This can even include network and power-distribution. In its simplest of configurations, user-facing access is one of the key services provided. Along with user-facing access services, the head node also provides other more important services to a cluster. 

Some of these services include:

  • Identity and Access Management: central point of connectivity to the system, enables users and instances to access services.
  • Configuration management: for performance, functionality and operations.
  • Scheduling Mechanism: Job Scheduler and workload manager resides here; applications such as slurm, Moab, Torque.
  • Storage and file transfer: place from which users store and transfer files.
  • Monitoring: where cluster monitoring and health checks are performed.
  • Interactive-use services: GUI based tools for code development including a command-line interface.
  • And, configuration of compute node for things like exporting home file system and applications file system.

Clusters are usually comprised of a single head node, but would not be recommended for large-scale use. One of the issues with a single head-node is the very high potential for exceeding resources. If too many users are requesting resources a single head node could easily become overwhelmed and as a consequence of this architecture, resilience to failure and continuity of service would be compromised.

Multiple head nodes may be the better practice because it ensures redundancy and responsiveness to the resources and services that are being provided. This is achieved by implementing multiple instances of each service across different head nodes. Plus, multiple head nodes are more favorable to cluster models, providing more than one single gateway to access the cluster and making it more evenly balanced across user access.

It’s also worth mentioning, the head node has usage constraints, such as the ability to act as a compute node. However, it will allow users to submit computational workloads acting as a 'submit-only node' within the context of the workload manager. 

Ideally you do not want to run computational programs on the head node itself. Meaning, any programs you want to run on the cluster should not be run on the head node. All usage should be restricted to the head node for programs that allow you to provision your cluster programs and manage and view your data.

The Head Node and Cluster Management Software

The head node is capable of performing management tasks all due to Cluster Management Software. Cluster Management Software is installed onto the head node, allowing users to manage a cluster through a graphical user interface or by accessing a command-line. Through Cluster Management Software a user can manage the entire cluster from low to high involvement activities.

At Exxact we’ve partner with Bright Computing to offer customers simplicity and flexibility. With built-in automation, integrated management and monitoring, our Bright Cluster Manager for HPC Solution lets you deploy complete clusters over bare metal and manage them effectively. It provides single-pane-of-glass management for the hardware, the operating system, HPC software, and users. With Bright, users receive the most powerful, vendor-independent cluster management software solution available.

If you’re interested in learning more about headnotes and our Bright Cluster Manager for HPC Solution, send us an inquiry today.

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Browse our whitepapers, e-books, case studies, and reference architecture.

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blog-what-is-a-head-node.jpg
HPC

Cluster Topology: What is a Head Node?

March 2, 2021 15 min read

The Importance of a Cluster Head Node

When working with a cluster there are a lot of operating pieces: switches, storage, compute nodes, applications, file systems, workloads, and more. The impact of unmanaged servers, storage, appliances and interactive sessions can lead to significant concerns, especially when it pertains to multiple users all competing eagerly for resources. Eventually user requests would outweigh the available resources and the results would be catastrophic! That's where the head node comes into play!

What is a Head Node?

In simple terms a head node, sometimes identified as a login node, is a configured system that sits in a Rack as part of a cluster and act as a Master node for the whole cluster in which case it becomes the single point for managing all the computational resources. It provides such things as management and scheduling services to the cluster;  it is considered to be one of the most important parts of a cluster and is essential to getting work done.

head-node-rack.png

In a cluster the head node provides services both internally and externally and, along with storage arrays and multiple compute nodes, as the name might suggest the head node is responsible for managing all of the resources within its control. This can even include network and power-distribution. In its simplest of configurations, user-facing access is one of the key services provided. Along with user-facing access services, the head node also provides other more important services to a cluster. 

Some of these services include:

  • Identity and Access Management: central point of connectivity to the system, enables users and instances to access services.
  • Configuration management: for performance, functionality and operations.
  • Scheduling Mechanism: Job Scheduler and workload manager resides here; applications such as slurm, Moab, Torque.
  • Storage and file transfer: place from which users store and transfer files.
  • Monitoring: where cluster monitoring and health checks are performed.
  • Interactive-use services: GUI based tools for code development including a command-line interface.
  • And, configuration of compute node for things like exporting home file system and applications file system.

Clusters are usually comprised of a single head node, but would not be recommended for large-scale use. One of the issues with a single head-node is the very high potential for exceeding resources. If too many users are requesting resources a single head node could easily become overwhelmed and as a consequence of this architecture, resilience to failure and continuity of service would be compromised.

Multiple head nodes may be the better practice because it ensures redundancy and responsiveness to the resources and services that are being provided. This is achieved by implementing multiple instances of each service across different head nodes. Plus, multiple head nodes are more favorable to cluster models, providing more than one single gateway to access the cluster and making it more evenly balanced across user access.

It’s also worth mentioning, the head node has usage constraints, such as the ability to act as a compute node. However, it will allow users to submit computational workloads acting as a 'submit-only node' within the context of the workload manager. 

Ideally you do not want to run computational programs on the head node itself. Meaning, any programs you want to run on the cluster should not be run on the head node. All usage should be restricted to the head node for programs that allow you to provision your cluster programs and manage and view your data.

The Head Node and Cluster Management Software

The head node is capable of performing management tasks all due to Cluster Management Software. Cluster Management Software is installed onto the head node, allowing users to manage a cluster through a graphical user interface or by accessing a command-line. Through Cluster Management Software a user can manage the entire cluster from low to high involvement activities.

At Exxact we’ve partner with Bright Computing to offer customers simplicity and flexibility. With built-in automation, integrated management and monitoring, our Bright Cluster Manager for HPC Solution lets you deploy complete clusters over bare metal and manage them effectively. It provides single-pane-of-glass management for the hardware, the operating system, HPC software, and users. With Bright, users receive the most powerful, vendor-independent cluster management software solution available.

If you’re interested in learning more about headnotes and our Bright Cluster Manager for HPC Solution, send us an inquiry today.

Free Resources

Browse our whitepapers, e-books, case studies, and reference architecture.

Explore

Topics