Amazon RDS Multi-AZ Synchronous Replication Now Supports ENA Express
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Introduction
On May 26, 2026, synchronous replication for RDS Multi-AZ gained support for ENA Express.
In an article published by Omura on the same day, the update was introduced in which ENA Express now supports cross-AZ communication and the single-flow bandwidth has been expanded to up to 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 charges | None | None |
| Enabling on existing instances | N/A | Stop and start, or change the instance class |
ENA Express is a technology that uses AWS's proprietary SRD (Scalable Reliable Datagram) protocol to raise the bandwidth of a single flow to up to 25 Gbps through congestion control and multipath routing. Improved synchronous replication performance can be expected for write-intensive workloads.
Targets and How to Enable
Supported Engines and Configurations
The supported engines are MySQL, PostgreSQL, MariaDB, Db2, and Oracle. SQL Server is not supported.
As for configurations, only Multi-AZ deployment (synchronous replication) is supported. Aurora (shared storage) and Single-AZ + Read Replica (asynchronous replication) are not supported.
Supported Instance Classes
The minimum configurations of RDS instance classes that support ENA Express are 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 classes such as m7g / r7g are not listed in the list of supported classes as of May 2026.
How to Enable
For new creation, specifying Multi-AZ with a supported instance class enables it by default. For existing instances, it is enabled by stopping and starting or by changing the instance class.
Conditions for Benefiting
The benefit is greater in environments where the bottleneck of synchronous replication is network bandwidth or latency. Specifically, these are environments where all of the following conditions are met: a supported instance class × Multi-AZ × high write load. In environments that had chosen 12xlarge / 16xlarge for the sake of network bandwidth, you may be able to consider scaling down to 8xlarge depending on CPU/memory requirements.
Trying to Check ENA Express from the RDS ENI
Since there is no field in the RDS API or console that shows whether ENA Express is enabled, I tried to see whether the ENI on the VPC side could be checked through the EC2 API.
Checking on EC2 (Baseline)
First, I enabled ENA Express on EC2 (m6i.8xlarge) and checked how it appears in the API as a baseline.
When enaSrdEnabled: true is set with ModifyNetworkInterfaceAttribute, it is displayed in describe-instances as follows.
"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, I was able to confirm the ENA Express state from both the API and CloudTrail.
Checking on RDS Multi-AZ
I created an RDS instance with db.m6i.8xlarge, MySQL 8.4.9, and Multi-AZ, and checked the ENIs (RDSNetworkInterface) that appeared in the VPC.
Two ENIs appeared, for the primary (us-west-2b) and the standby (us-west-2a), but the EnaSrdSpecification field was not displayed on either of them.
{
"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 I checked, no ENA Express-related operations were recorded in CloudTrail either.
Why It Isn't Visible
At least from the RDSNetworkInterface visible on the VPC side, I could not confirm the state of ENA Express used for cross-AZ replication. It is possible that the replication path is managed at a layer separate from the ENI attributes that customers can reference (speculation).
Summary
If you run Multi-AZ on ENA Express-compatible instances, you can expect improved synchronous replication performance at no additional charge. For existing environments, it is enabled by stopping and starting or by changing the instance class. If you are using a supported class in an environment with a high replication load, please check the effect of the update.
Also, for environments with a high write load on older generations (such as m5), this could be a good opportunity to consider updating to the m6i generation, which supports ENA Express. Together with recent RDS improvements such as Optimized Reads and Optimized Writes, I recommend exploring room for cost optimization.
