Add 4.3.0 release notes

Author: ansd

release-notes/4.3.0.md

@@ -0,0 +1,85 @@
+## RabbitMQ 4.3.0
+
+
+## Breaking Changes and Compatibility Notes
+
+TBD
+
+
+## Release Highlights
+
+TBD
+
+
+## Upgrading to 4.3.0
+
+### Documentation guides on upgrades
+
+See the [Upgrading guide](https://www.rabbitmq.com/docs/upgrade) for documentation on upgrades and [GitHub releases](https://github.com/rabbitmq/rabbitmq-server/releases)
+for release notes of individual releases.
+
+This release series supports upgrades from `4.2.x`.
+
+
+### New Required Feature Flags
+
+All feature flags introduced in `4.2.0` and earlier are required, including the following:
+* `rabbitmq_4.2.0`
+* `rabbitmq_4.1.0`
+* `rabbitmq_4.0.0`
+* `khepri_db`
+* `quorum_queue_non_voters`
+* `message_containers_deaths_v2`
+
+Enable all required feature flags before upgrading to `4.3.0`.
+
+If your RabbitMQ cluster had plugin `rabbitmq_amqp1_0` enabled in RabbitMQ `3.13.x` (and your cluster still serves AMQP 1.0 client connections in `4.x`), your cluster should do at least one rolling update **after** enabling feature flag `rabbitmq_4.0.0` but **before** upgrading to `4.3.0`.
+
+### Deprecated Features
+
+In `4.3.0` the deprecation phase of the following features advanced from `permitted_by_default` to `denied_by_default`:
+* `amqp_filter_set_bug`
+
+### Mixed version cluster compatibility
+
+RabbitMQ 4.3.0 nodes can run alongside `4.2.x`.
+
+Mixed version clusters are a mechanism that allows rolling upgrade and are not meant to be run for extended
+periods of time (no more than a few hours).
+
+### Recommended Post-upgrade Procedures
+
+This version does not require any additional post-upgrade procedures
+compared to other versions.
+
+
+## Changes Worth Mentioning
+
+### Core Server
+
+#### Enhancements
+
+TBD
+
+### HTTP Auth Backend
+
+#### Enhancements
+
+The HTTP Auth Backend can now optionally provide a custom authorization denial reason to AMQP clients.
+To opt in, return `deny <Reason>` (instead of only `deny`) in the HTTP response body of your HTTP auth backend and set the following in your `rabbitmq.conf` file:
+```ini
+auth_http.authorization_failure_disclosure = true
+```
+
+See the [README](https://github.com/rabbitmq/rabbitmq-server/blob/main/deps/rabbitmq_auth_backend_http/README.md) for more information.
+
+Pull Request: [#14641](https://github.com/rabbitmq/rabbitmq-server/pull/14641)
+
+### Dependency Changes
+
+TBD
+
+## Source Code Archives
+
+To obtain source code of the entire distribution, please download the archive named `rabbitmq-server-4.3.0.tar.xz`
+instead of the source tarball produced by GitHub.