Amazon RDS Multi-AZ synchronous replication now supports ENA Express
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Introduction
On May 26, 2026, RDS Multi-AZ synchronous replication added support for ENA Express.
On the same day, an article published by Omura introduced the update in which ENA Express gained support for cross-AZ communication, expanding the single-flow bandwidth to a maximum of 25 Gbps.
| Item | Before | After ENA Express Support |
|---|---|---|
| Single-flow bandwidth for cross-AZ replication | Up to 5 Gbps | Up to 25 Gbps |
| Latency variability | Standard | Reduced (congestion control and multipath via SRD) |
| Additional cost | None | None |
| Enabling on existing instances | N/A | Stop/start or instance class change |
ENA Express uses AWS's proprietary SRD (Scalable Reliable Datagram) protocol, a technology that raises single-flow bandwidth to a maximum of 25 Gbps through congestion control and multipath routing. Performance improvements in synchronous replication are expected for write-intensive workloads.
Target Configurations and How to Enable
Supported Engines and Configurations
The supported engines are MySQL, PostgreSQL, MariaDB, Db2, and Oracle. SQL Server is not supported.
In terms of configuration, only Multi-AZ deployments (synchronous replication) are supported. Aurora (shared storage type) and Single-AZ + Read Replica (asynchronous replication) are not supported.
Supported Instance Classes
The minimum configuration for RDS instance classes that support ENA Express is as follows.
| Category | Minimum Instance Class | vCPU | Memory |
|---|---|---|---|
| General Purpose | db.m6i.8xlarge | 32 | 128 GiB |
| Memory Optimized | db.r6i.8xlarge | 32 | 256 GiB |
Graviton3 generation instances such as m7g / r7g are not listed in the supported list as of May 2026.
How to Enable
For new instances, ENA Express is enabled by default when specifying Multi-AZ with a supported instance class. For existing instances, it is enabled by stopping/starting the instance or changing the instance class.
Conditions for Benefiting
The benefit is greatest in environments where the bottleneck in synchronous replication lies in network bandwidth or latency. Specifically, environments that meet all of the following conditions: a supported instance class × Multi-AZ × high write load. Environments that were choosing 12xlarge / 16xlarge for network bandwidth purposes may be able to consider scaling down to 8xlarge depending on CPU/memory requirements.
Attempting to Verify ENA Express via RDS ENIs
Since there is no field in the RDS API or console indicating the ENA Express enabled state, I tried to see if it could be checked from the VPC-side ENI via the EC2 API.
Verification on EC2 (Baseline)
First, I enabled ENA Express on an EC2 instance (m6i.8xlarge) and checked how it appears in the API as a baseline.
When setting enaSrdEnabled: true via ModifyNetworkInterfaceAttribute, it is displayed as follows in describe-instances.
"Attachment": {
"EnaSrdSpecification": {
"EnaSrdEnabled": true
}
}
The operation is also recorded in CloudTrail.
CloudTrail event (ModifyNetworkInterfaceAttribute)
{
"eventName": "ModifyNetworkInterfaceAttribute",
"requestParameters": {
"networkInterfaceId": "eni-0xxxxxxxxxxxxxxxxx",
"enaSrdSpecification": {
"enaSrdEnabled": true
}
}
}
On EC2, the ENA Express state could be confirmed from both the API and CloudTrail.
Verification on RDS Multi-AZ
I created an RDS instance with db.m6i.8xlarge, MySQL 8.4.9, and Multi-AZ, then inspected the ENI (RDSNetworkInterface) that appeared in the VPC.
Two ENIs appeared for the primary (us-west-2b) and standby (us-west-2a), but neither displayed the EnaSrdSpecification field.
{
"NetworkInterfaceId": "eni-0xxxxxxxxxxxxxxxxx",
"Description": "RDSNetworkInterface",
"RequesterId": "amazon-rds",
"RequesterManaged": true,
"Attachment": {
"AttachmentId": "eni-attach-0xxxxxxxxxxxxxxxxx",
"InstanceOwnerId": "amazon-rds",
"Status": "attached"
}
}
It was consistently not displayed throughout the entire process from creating to available. Within the scope of my investigation, no ENA Express-related operations were recorded in CloudTrail either.
Why It Is Not Visible
At least from the RDSNetworkInterface visible on the VPC side, the ENA Express state used for cross-AZ replication could not be confirmed. It is possible (estimated) that the replication path is managed at a layer separate from the ENI attributes accessible to customers.
Summary
In environments running Multi-AZ with ENA Express-supported instances, performance improvements in synchronous replication can be expected at no additional cost. For existing environments, this is enabled by stopping/starting the instance or changing the instance class. If you are running a workload with high replication load on a supported instance class, please verify the effect of this update.
Additionally, for environments on older generations (such as m5) with high write loads, this may be a good opportunity to consider upgrading to the m6i generation, which supports ENA Express. Along with recent RDS improvements such as Optimized Reads and Optimized Writes, we recommend exploring opportunities for cost optimization.
