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Add support for Netty 4.2.x #6757
Description
Describe the bug
When upgrading an application stack to Netty 4.2.x and Reactor Netty 1.3.x, the AWS SDK v2 netty-nio-client fails when providing a Netty 4.2-style EventLoopGroup (e.g. MultiThreadIoEventLoopGroup).
The failure occurs because SdkEventLoopGroup create does not recognize MultiThreadIoEventLoopGroup (Netty 4.2 model) and throws:
IllegalArgumentException: Unknown event loop group : class io.netty.channel.MultiThreadIoEventLoopGroup
This suggests that netty-nio-client still expects 4.1-style EpollEventLoopGroup or NioEventLoopGroup.
So few Key Questions
- Does AWS SDK v2 officially support Netty 4.2.x?
- If not:
- Is there a roadmap to support 4.2?
- Is there an estimated release version? - If yes:
- Which AWS SDK version should be used?
- What is the correct way to provide a 4.2-style IoEventLoopGroup? - Is there a recommended compatibility matrix between:
- AWS SDK v2
- Netty
Regression Issue
- Select this option if this issue appears to be a regression.
Expected Behavior
If AWS SDK v2 supports Netty 4.2.x:
SdkEventLoopGroupcreate should acceptIoEventLoopGroup/MultiThreadIoEventLoopGroup- OR documentation should clearly state that Netty 4.2.x is not supported
Current Behavior
Only 4.1-style groups are supported:
- EpollEventLoopGroup
- KQueueEventLoopGroup
- NioEventLoopGroup
IoEventLoopGroup (4.2 model) is not recognized.
Reproduction Steps
- Create Netty 4.2 EventLoopGroup
@Bean
public EventLoopGroup eventLoopGroup() {
return new MultiThreadIoEventLoopGroup(
8,
NioIoHandler.newFactory()
);
}
- Provide it to AWS SDK
@Bean
public SdkEventLoopGroup sdkEventLoopGroup(EventLoopGroup eventLoopGroup) {
return SdkEventLoopGroup.create(
eventLoopGroup,
NioSocketChannel::new
);
}
- Result
IllegalArgumentException:
Unknown event loop group :
class io.netty.channel.MultiThreadIoEventLoopGroup
Possible Solution
-
Add support for Netty 4.2
IoEventLoopGroup- Detect
IoEventLoopGroup/MultiThreadIoEventLoopGroup - Allow user-provided
ChannelFactorywithout strict type checking - Avoid instanceof checks tied to 4.1-only classes
- Detect
-
Provide explicit documentation
- Clearly state that Netty 4.2.x is not supported
- Provide an official compatibility matrix
-
Introduce version-aware factory logic
- If Netty 4.2 detected, use generic
ChannelFactory - Avoid relying on concrete
EventLoopGroupsubclass checks
- If Netty 4.2 detected, use generic
At minimum, clarification on official Netty 4.2 support status would help users avoid runtime incompatibilities during upgrades.
Additional Information/Context
Netty 4.2 introduces the new IoHandler model and deprecates:
EpollEventLoopGroup, KQueueEventLoopGroup, NioEventLoopGroup
Frameworks such as Reactor Netty 1.3.x are beginning to align with 4.2 APIs.
This creates a compatibility gap for applications using: Spring WebFlux / Reactor Netty, AWS SDK v2 async clients, Shared EventLoopGroups for IO optimization
Currently, users must either - Downgrade Netty to 4.1.x Or use deprecated EventLoopGroup implementations
Clarification on official support would help prevent production incompatibilities.
The incompatibility appears to stem from SdkEventLoopGroup performing instance checks against legacy EventLoopGroup types.
AWS Java SDK version used
V2 SDK (group ID software.amazon.awssdk) - 2.42.4
JDK version used
Java 21
Operating System and version
Linux (Epoll available)
Activity
debora-ito commentedon Mar 6, 2026
Hi @samarprakash
aws-sdk-java-v2/pom.xml
Line 121 in f61e386
The latest Java SDK version uses Netty 4.1.130, but we have plans to upgrade to 4.2.x and we're aware of the changes required to support it. Tracking in PR: #6205.
We are currently working to remove some blockers to merge the PR, will post updates here when we have any.
dragonsahead commentedon Apr 14, 2026
Can you turn this into a P1? old Netty versions have vulnerabilities that need to be solved in order to deploy software in a production environment
debora-ito commentedon Apr 14, 2026
@dragonsahead the latest Java SDK version uses Netty
4.1.132.Finaland doesn't show any vulnerabilities. Are you able to upgrade to the latest SDK version?dragonsahead commentedon Apr 15, 2026
We can’t use 4.1 due to other driver we have that need 4.2
mseidel commentedon Apr 15, 2026
Spring Boot 4 just released with Netty 4.2 so that alone will break a ton of stuff
cmcclung-ANGENG commentedon May 1, 2026
You don't have to use the new MultiThreadIoEventLoopGroup, can you use the old APIs ie
EventLoopGroup group = new NioEventLoopGroup();
On the sdk side moving to 4.2.x makes sense but wait for 4.2.13
fdubuisson-betclic commentedon May 18, 2026
Netty 4.2.13 was released 2 weeks ago so is there an ETA for its integration in the SDK ?
Many frameworks have updated and are now conflicting with the SDK (in our case, the Ktor framework)
guillaume-verdon-sword commentedon Jun 24, 2026
Hello everyone,
Springboot 3 will be out of open source support very soon.
As mentionned above, Springboot 4 now relies on Netty 4.2 which is not binary compatible with Netty 4.1.
If my understanding is correct, it will soon be impossible to use both a supported version of AWS SDK and a supported version of Springboot.
@debora-ito I suggest raising the priority for this bug to P1 before this ticking bomb hits everyone.
Regards,
Guillaume
stewue commentedon Aug 10, 2026
any updates on this one?
paulodoh27-sketch commentedon Aug 10, 2026
Launch thread application launcher on chain
cmcclung-ANGENG commentedon Aug 10, 2026
For visibility Netty is going towards a 5.0 release at some point and has started to discuss EOL for 4.1
So doing some work towards supporting a few versions might be a good idea
vstamate commentedon Aug 23, 2026
In the same manner, Spring Boot 4 and Gatling 3.15.0 uses netty 4.2.
build(deps): bump Reactor and Netty BOMs to the latest 4.1-line releases
[-]AWS SDK v2 netty-nio-client incompatible with Netty 4.2.x IoEventLoopGroup (MultiThreadIoEventLoopGroup not recognized)[/-][+]Add support for Netty 4.2.x[/+]sandeepvinayak commentedon Oct 5, 2026
@debora-ito @zoewangg This came up during the upgrade to spring boot 4 at our organization, I think at this moment upgrade to netty 4.2 should be treated as P1/P0 for aws java v2.