[Proposal] Release the First Apache BifroMQ (Incubating) Version (4.0.0-incubating)

[popduke]

Since the last non-Incubator release (v3.3.5), BifroMQ has received a number of architectural updates, operational improvements, and bug fixes.
Because many internal components were refactored—and due to the required Apache compliance adjustments—this release is not backward-compatible with previous non-Incubator versions. Users should plan this as a major upgrade.

About the version number:
The 4.0.0-incubating version number reflects continuity from the pre-Incubator lineage while marking a new phase under the Apache Incubator.

Below is a brief summary of what the 4.0.0-incubating release contains.

1. Major New Features

• Support for “Independent Workload Cluster (IWC)” deployment mode
  Enabling MQTTServer, DistService, InboxService, RetainService, SessionDictService, and APIServer to run as separate workload clusters for improved scaling and resource isolation.

• New Plugin: ClientBalancer
  Allows integrating custom client-balancing strategies to manage MQTT client connection distribution more effectively.

• New SPIs and Hook Points for Deep Customization
  Multiple new extension points at different levels have been added to support advanced integration and extension use cases.

• New APIs for Cluster Landscape Inspection, RPC Traffic Governance, and StoreBalancer Management
  These APIs provide better visibility into cluster composition, more control over store-balancing behavior, and the ability to govern internal RPC traffic patterns.

2. Improvements in Architecture and Core Capabilities

• Various improvements to base-cluster and base-crdt for reduced overhead and faster convergence.

• Refactored base-rpc to support more graceful rebalancing behavior and reduce disruption during topology changes.

• Refactored base-kv to improve resilience and make the system more pluggable and extensible.

• Refactored base-scheduler with improved observability and easier customization of scheduling logic.

• Optimized internal RPC protocol and storage schemes across DistService, InboxService, and RetainService for better load distribution and more predictable performance.

3. Apache Compliance Work

• Updated LICENSE and NOTICE with correct third-party attributions.
• Normalized source headers and Java package paths under org.apache.bifromq.
• Added DISCLAIMER and other ASF-required metadata.
• Updated build and distribution scripts to produce Apache-compliant source releases.
• Updated SSL/TLS handling: the default build does not bundle any SSL implementation; users may optionally build variants with their preferred SSL library.

4. Next Steps

• Keep this discussion open for feedback for approximately one week.
• Prepare the 4.0.0-incubating RC1 and upload it to the ASF dev distribution area.
• Initiate the [VOTE] thread on dev@ once the review window closes.
• Address any findings and iterate with additional RCs if necessary.

Feedback on this proposal and on the summarized changes is welcome.

[RogerGGX]

Very interesting project.
I'm looking forward this release version.

[jennifer88huang]

Congratulations to the entire BifroMQ team and community on this monumental release! The launch of version 4.0.0-incubating marks a significant milestone in the project's journey within the Apache Incubator.

[Gujiawei-Edinburgh]

Impressive optimizations! I’ll update the corresponding sections on the official website to reflect these changes.

[mahongweichina]

It is an excellent project from Baidu that addresses important needs in the industry. We are even more confident in its potential as it enters the Apache Incubator.

[ZHANGSHUNLIN]

The new module layout and more flexible architecture demonstrate powerful potential. We eagerly anticipate future iterations and improvements.

[visoar]

Exciting progress!
Looking forward to the 4.0.0-incubating release and the upcoming RC review.
We could also take this chance to give the website a fresh update.

[liaodn]

+1 (non-binding)
Thanks for the detailed release notes. This looks like a solid release with significant architectural improvements. I support moving forward with the RC1 vote.