RabbitMQ `3.9.4` is a maintenance release in the `3.9.x` release series.
Please refer to the **Upgrading to 3.9** section from [v3.9.0 release notes](https://github.com/rabbitmq/rabbitmq-server/releases/tag/v3.9.0) if upgrading from a version prior to 3.9.0.
This release requires at least Erlang 23.2, and supports the latest Erlang 24 version, 24.0.5 at the time of release. [RabbitMQ and Erlang/OTP Compatibility Matrix](https://www.rabbitmq.com/which-erlang.html) has more details on Erlang version requirements for RabbitMQ.
## Changes Worth Mentioning
Release notes are kept under [rabbitmq-server/release-notes](https://github.com/rabbitmq/rabbitmq-server/tree/v3.9.x/release-notes).
Contributors are encouraged to update them together with their changes. This helps with release automation and more
consistent release schedule.
### Core Server
#### Enhancements
* Nodes will now use four more environment variables, if set: `RABBITMQ_DEFAULT_USER` (overrides `default_user` in `rabbitmq.conf`), `RABBITMQ_DEFAULT_PASS` (overrides `default_pass`), `RABBITMQ_DEFAULT_VHOST` (overrides `default_vhost`) and `RABBITMQ_ERLANG_COOKIE` (sets [shared authentication secret value](https://www.rabbitmq.com/clustering.html#erlang-cookie)).
These variables **are not recommended to be used in production** but can be the only realistic option in some environment, such as service containers, ECS, and so on.
Most users should continue using `rabbitmq.conf` and a securely generated local cookie file.
* Definitions now can be imported from different sources, including those provided by plugins. Original local filesystem source is still supported in a backwards-compatible way.
To obtain source code of the entire distribution, please download the archive named `rabbitmq-server-3.9.4.tar.xz` instead of the source tarball produced by GitHub.