CFD Direct has launched CFDDFC® (Arm), a marketplace product on Amazon Web Services (AWS) for computational fluid dynamics (CFD) with OpenFOAM. CFDDFC (Arm) is a variant of CFD Direct From the Cloud™ for Amazon EC2 instances running Arm-based Graviton2 processors, in particular the C6g instances for compute-intensive workloads. CFDDFC (Arm) operates in server-mode without graphical applications and includes:

Comparison of C6g and C5n instances

We ran a steady-state external aerodynamics simulation of 4 million cells with simpleFoam in parallel for 5000 iterations on the largest C6g and C5n instances. C5n instances use Intel’s Skylake-SP processors with standard x86 architecture. The largest instance, c5n.18xlarge, provided 72 vCPUs (virtual CPUs) which equates to 36 physical cores since the processors include hyper-threading. Hyper-threading offers nothing for parallel running with OpenFOAM so our parallel simulation involved decomposing and running on 36 subdomains. The largest C6g instance, c6g.16xlarge, provides 64 vCPUs which means 64 physical cores, since there is no hyper-threading. The parallel simulation used 64 subdomains.

The simulation timings are costs of on-demand EC2 are shown below. By comparing (simulation time × cores) for C6g and C5n in this simulation, 2.07 C6g cores deliver the same performance as 1 C5n core. The C5n core-hr price is $0.108, compared to $0.034 for C6g. At equivalent price-performance (multiplying by 2.07), C6g is $0.070 per core-hr, resulting in the 35% saving over C5n. This is consistent with the 40% savings with C6g instances over a range of test cases conducted by AWS.

Instance c5n.18xlarge c6g.16xlarge
Physical cores 36 64
Simulation time (s) 5614 6547
EC2 cost $3.888/hr → $6.06 $2.176/hr → $3.95


Users of CFD Direct From the Cloud™ now have the choice of marketplace products from CFD Direct:

No Remote Desktop with CFDDFC (Arm)

Arm-based processors do not have the same level of software support as the x86 architectures. They are largely confined to server based  operating systems without graphical applications. CFDDFC (Arm) runs on Ubuntu Server for Arm, so does not support the remote desktop provided with the standard CFDDFC on x86.

No Saving with Spot Pricing with CFDDFC (Arm)

At the time of writing (2020-07-08), the advertised Spot Instance Pricing in the us-east-1 region is $1.1659/hr for c5n.18xlarge. and $1.0882/hr for c6g.16xlarge. At those prices the EC2 cost for our simulation would have been $1.82 and $1.98 respectively, making C6g slightly more expensive.

Command Line Interface

The cfddfc command line interface (CLI) manages instances of CFDDFC on AWS, transfers data to and from instances and provides simple SSH login.  It now includes the new CFDDFC (Arm) product for C6g family of instances. It is well designed to run batch jobs, since instances can be simply launched with a command such as the following.

cfddfc launch -instance c6g.2xlarge -region us-east-1

The user can then create a cluster of 4 instances by adding 3 slave instances using the cluster subcommand, e.g.

cfddfc cluster -slaves 3

Once the slave instances are running, the cluster is fully operational.

CFDDFC (Arm) for AWS C6g