Network architecture
| HPCPERF05: How do you select your network solution? |
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Loosely and tightly coupled workloads have different network communication patterns and needs. When selecting your network solution, consider your workload's network latency, bandwidth, and throughput requirements.
HPCPERF05-BP01 Consider latency, bandwidth, and throughput requirements for HPC workloads
The optimal network solution for an HPC workload varies based on latency, bandwidth, and throughput requirements. Tightly coupled HPC applications often require the lowest latency possible for network connections between compute nodes. For moderately sized, tightly coupled workloads, it is possible to select a large instance type with a large number of cores so that the application fits entirely within the instance without crossing the network at all.
Alternatively, some applications are network bound and require
high network performance. Instances with higher network
performance can be selected for these applications. The highest
network performance is usually obtained with the largest
instance type in a family. Refer to the
Amazon EC2 Instance types
Implementation guidance
Use cluster placement groups and Elastic Fabric Adapter for tightly coupled applications.
Multiple instances with low latency between the instances are required for large tightly coupled applications. On AWS, this is achieved by launching compute nodes into a cluster placement group, which is a logical grouping of instances within an Availability Zone. A cluster placement group provides non-blocking and non-oversubscribed connectivity, including full bisection bandwidth between instances. Use cluster placement groups for latency sensitive tightly coupled applications spanning multiple instances.
In addition to cluster placement groups, tightly coupled applications benefit from Elastic Fabric Adapter (EFA), a network device that can attach to your Amazon EC2 instance. EFA provides lower and more consistent latency and higher throughput than the TCP transport traditionally used in cloud-based HPC systems. It enables an OS-bypass access model through the Libfabric API that allows HPC applications to communicate directly with the network interface hardware. EFA enhances the performance of MPI and NCCL inter-instance communication, is optimized to work on the existing AWS network infrastructure, and is critical for scaling tightly coupled applications.
If an application cannot take advantage of EFA's OS-bypass functionality, or an instance type does not support EFA, optimal network performance can be obtained by selecting an instance type that supports Elastic Network Adapter (ENA) or ENA Express. ENA provides EC2 instances with higher networking performance and lower CPU utilization through the use of pass-through rather than hardware-emulated devices. This method allows EC2 instances to achieve higher bandwidth, higher packet-per-second processing, and lower inter-instance latency compared to traditional device virtualization.
ENA is available on all current-generation instance types and requires an AMI with supported drivers. Although most current AMIs contain supported drivers, custom AMIs may require updated drivers. For more information on enabling enhanced networking and instance support, refer to the Enhanced networking on Amazon EC2 instances.
ENA Express is an ENA feature that can be enabled on certain EC2 instances and it is designed to increase the single flow bandwidth and lower the tail latency of network traffic between EC2 instances. Workloads such as distributed storage systems and live media encoding that require large flows and are sensitive to variance in latency can benefit from ENA Express.
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Distribute your jobs across multiple Availability Zones or Regions for loosely coupled workloads.
Loosely coupled workloads are generally not sensitive to very low-latency networking and do not require the use of a cluster placement group or the need to keep instances in the same Availability Zone or Region.
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Use the Instance Type Matrix to determine the right instance type for your network bandwidth needs.
In some cases, the available network bandwidth depends on the
type of network traffic. For example, HPC optimized instances,
can access a higher network bandwidth when used together with
EFA. The
Amazon EC2 Instance types
Key AWS services
Resources
