Elastic Fabric Adapter
An Elastic Fabric Adapter (EFA) is a network device that you can attach to your Amazon EC2 instance to accelerate High Performance Computing (HPC) and machine learning applications. EFA enables you to achieve the application performance of an on-premises HPC cluster, with the scalability, flexibility, and elasticity provided by the AWS Cloud.
EFAs provide lower and more consistent latency and higher throughput than the TCP transport traditionally used in cloud-based HPC systems. It enhances the performance of inter-instance communication that is critical for scaling HPC and machine learning applications. It is optimized to work on the existing AWS network infrastructure and it can scale depending on application requirements.
EFAs integrate with Libfabric 1.7.0 and later and it supports Open MPI 3.1.3 and later and Intel MPI 2019 Update 5 and later for HPC applications, and Nvidia Collective Communications Library (NCCL) for machine learning applications.
Note
The OS-bypass capabilities of EFAs are not supported on Windows instances. If you attach an EFA to a Windows instance, the instance functions as an Elastic Network Adapter, without the added EFA capabilities.
Contents
EFA basics
An EFA is an Elastic Network Adapter (ENA) with added capabilities. It provides all of the functionality of an ENA, with an additional OS-bypass functionality. OS-bypass is an access model that allows HPC and machine learning applications to communicate directly with the network interface hardware to provide low-latency, reliable transport functionality.

Traditionally, HPC applications use the Message Passing Interface (MPI) to interface with the system’s network transport. In the AWS Cloud, this has meant that applications interface with MPI, which then uses the operating system's TCP/IP stack and the ENA device driver to enable network communication between instances.
With an EFA, HPC applications use MPI or NCCL to interface with the Libfabric API. The Libfabric API bypasses the operating system kernel and communicates directly with the EFA device to put packets on the network. This reduces overhead and enables the HPC application to run more efficiently.
Note
Libfabric is a core component of the OpenFabrics Interfaces (OFI) framework,
which defines and exports the user-space API of OFI. For more information, see
the Libfabric OpenFabrics
Differences between EFAs and ENAs
Elastic Network Adapters (ENAs) provide traditional IP networking features that are required to support VPC networking. EFAs provide all of the same traditional IP networking features as ENAs, and they also support OS-bypass capabilities. OS-bypass enables HPC and machine learning applications to bypass the operating system kernel and to communicate directly with the EFA device.
Supported interfaces and libraries
EFAs support the following interfaces and libraries:
-
Open MPI 3.1.3 and later
-
Open MPI 4.0 or newer is preferred for Graviton
-
Intel MPI 2019 Update 5 and later
-
NVIDIA Collective Communications Library (NCCL) 2.4.2 and later
Supported instance types
The following instance types support EFAs:
-
General purpose:
m5dn.24xlarge
|m5dn.metal
|m5n.24xlarge
|m5n.metal
|m5zn.12xlarge
|m5zn.metal
|m6a.48xlarge
|m6a.metal
|m6i.32xlarge
|m6i.metal
|m6id.32xlarge
|m6id.metal
|m6idn.32xlarge
|m6idn.metal
|m6in.32xlarge
|m6in.metal
|m7g.16xlarge
|m7g.metal
-
Compute optimized:
c5n.9xlarge
|c5n.18xlarge
|c5n.metal
|c6a.48xlarge
|c6a.metal
|c6gn.16xlarge
|c6i.32xlarge
|c6i.metal
|c6id.32xlarge
|c6id.metal
|c6in.32xlarge
|c6in.metal
|c7g.16xlarge
|c7g.metal
|hpc6a.48xlarge
-
Memory optimized:
hpc6id.32xlarge
|r5dn.24xlarge
|r5dn.metal
|r5n.24xlarge
|r5n.metal
|r6a.48xlarge
|r6a.metal
|r6i.32xlarge
|r6i.metal
|r6idn.32xlarge
|r6idn.metal
|r6in.32xlarge
|r6in.metal
|r6id.32xlarge
|r6id.metal
|r7g.16xlarge
|r7g.metal
|x2idn.32xlarge
|x2idn.metal
|x2iedn.32xlarge
|x2iedn.metal
|x2iezn.12xlarge
|x2iezn.metal
-
Storage optimized:
i3en.12xlarge
|i3en.24xlarge
|i3en.metal
|i4g.16xlarge
|i4i.32xlarge
|i4i.metal
|im4gn.16xlarge
-
Accelerated computing:
dl1.24xlarge
|g4dn.8xlarge
|g4dn.12xlarge
|g4dn.16xlarge
|g4dn.metal
|g5.8xlarge
|g5.12xlarge
|g5.16xlarge
|g5.24xlarge
|g5.48xlarge
|inf1.24xlarge
|p3dn.24xlarge
|p4d.24xlarge
|p4de.24xlarge
|trn1.32xlarge
|trn1n.32xlarge
|vt1.24xlarge
To see the available instance types that support EFAs in a specific Region
The available instance types vary by Region. To see the available instance types that
support EFAs in a Region, use the describe-instance-types
command with the --region
parameter. Include the --filters
parameter to scope the results to the instance types that support EFA and the
--query
parameter to scope the output to the value of
InstanceType
.
aws ec2 describe-instance-types --region
us-east-1
--filters Name=network-info.efa-supported,Values=true --query "InstanceTypes[*].[InstanceType]" --output text | sort
Supported operating systems
The following operating systems support EFAs with Intel/AMD x86-based instance types:
Amazon Linux 2
CentOS 7
RHEL 7 and 8
Debian 10
Rocky Linux 8 and 9
Ubuntu 20.04 and 22.04
SUSE Linux Enterprise 15 SP2 and later
OpenSUSE Leap 15.4 and later
Note
Ubuntu 20.04 supports peer direct support when used with dl1.24xlarge
instances.
The following operating systems support EFAs with Arm-based (Graviton) instance types:
Amazon Linux 2
RHEL 8 and Rocky Linux 8 and 9
Debian 10
Ubuntu 20.04 and 22.04
SUSE Linux Enterprise 15 SP2 and later
EFA limitations
EFAs have the following limitations:
-
All
p4d
instance types support NVIDIA GPUDirect Remote Direct Memory Access (RDMA). -
Instance types that support multiple network cards can be configured with one EFA per network card. All other supported instance types support only one EFA per instance.
-
For
c7g.16xlarge
,m7g.16xlarge
andr7g.16xlarge
Dedicated Instances and Dedicated Hosts are not supported when an EFA is attached. -
EFA OS-bypass traffic is limited to a single subnet. In other words, EFA traffic cannot be sent from one subnet to another. Normal IP traffic from the EFA can be sent from one subnet to another.
-
EFA OS-bypass traffic is not routable. Normal IP traffic from the EFA remains routable.
-
The EFA must be a member of a security group that allows all inbound and outbound traffic to and from the security group itself.
EFA is not supported on AWS Outposts