Project: RabbitMQ (App Definition and Development / Streaming & Messaging)
File: 3.9.0.md

The most important changes are , support for , and improved integration with our . Other changes worth mentioning are JSON logging, per-protocol and queue type message rates as Prometheus metrics and faster initial cluster formation on Kubernetes. Find blog posts that expand on the previously mentioned topics: https://blog.rabbitmq.com/tags/v3.9.x/ are a new persistent and replicated data structure ("queue type") in RabbitMQ which models an append-only log with non-destructive consumer semantics. They can be used as a regular AMQP 0.9.1 queue or through a new and associated client(s). Streams enable messaging patterns that were not possible or practical before, for example, repeatable non-destructive consumption and mass fanouts to a very large number of consumers. provides 20%-50% higher throughput for many workloads tested by the RabbitMQ core team and community members. Supporting the latest runtime version also allowed RabbitMQ to replace a few external dependencies with libraries now provided by the runtime. Erlang 24 is now used by default in the . automates provisioning, management, and operations of RabbitMQ clusters running on Kubernetes. It is and is developed by the RabbitMQ Core team at VMware, Inc. This Operator is not specific to 3.9 and can be used with latest 3.8.x release series. makes it possible to define RabbitMQ resources (virtual hosts, users, permissions, topologies, policies, etc) as Kubernetes objects. This Operator is also and can be used with latest 3.8.x release series. introduces an option for structured logging in JSON. This is relevant for the Prometheus-based alerting feature that we have been investing in this year: . RabbitMQ releases are distributed via , , and . This release or later. Erlang 24 is recommended as it for many workloads. explains what package repositories and tools can be used to provision latest patch versions of Erlang 23.3.x and 24.x. See the for documentation on upgrades and for release notes of other releases. RabbitMQ 3.9.0 nodes can run alongside `3.8.x` nodes. However, `3.8.16+` as well as `3.9.x` both require Erlang 23.2 or later (and support 24). `3.9.x`-specific features can only be made available when all nodes in the cluster upgrade to 3.9.0 or any other patch release in the series. While operating in mixed version mode, some aspects of the system may not behave as expected. The list of known behavior changes is covered below. Once all nodes are upgraded to 3.9.0, these irregularities will go away. 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). In a mixed version cluster, declaration of new quorum queues will fail if executed on a node in the version

For example, in a five node cluster with two nodes running 3.8, the three 3.9 nodes are in the version majority and the remaining are in the version minority. Existing quorum queues will operate just like before. HTTP API responses will provide a or metrics for a limited number of queues (for operations such as `GET /api/queues/{vhost}`) when operating in mixed version mode. Client libraries that were compatible with RabbitMQ `3.8.x` will be compatible with `3.9.0`. RabbitMQ `3.8.16` and later require Erlang `23.2` and support Erlang `24` (recommended). Users of RabbitMQ versions that should first upgrade to the latest `3.8.x` patch release on Erlang 23.2, then upgrade to `3.9.0`, and ideally Erlang 24. Any questions about this release, upgrades or RabbitMQ in general are welcome on the . Release notes are kept under . Contributors are encouraged to update them together with their changes. This helps with release automation and more consistent release schedule. , a new durable replicated data structure that allows for repeatable (non-destructive) consumption. RabbitMQ 3.9 introduces a new binary protocol for working with streams. While streams can be used by AMQP 0-9-1 clients, in most cases it will be used via a client. The new protocol exposes all the operations specific to this queue type and is heavily optimized for them, resulting in much higher read and write throughput. and clients Structural logging in JSON. Nodes can now log in JSON format. GitHub issue: no longer uses randomized startup delay to ensure only one node starts as a seed one during initial (parallel) cluster formation. Instead it relies on an internal runtime locking library. GitHub issue: Binding recovery on node startup is now more efficient. This means in clusters with a lot of queues and/or bindings, nodes start quicker. GitHub issue: Classic mirrored queue replcas are now started synchronously. GitHub issue: `journald` notifications are now performed using a library and not an external tool (`socat`) GitHub issue: Startup banner now provides more information some of which can be customised. GitHub issues: , Per-protocol and queue type message rates are now available as Prometheus metrics, as well as Streams-specific errors. This also addresses a long-standing 3.8.x counters issue for most metrics of this type, as captured in . GitHub issues: , , Standard runtime logger is now used for logging instead of Lager, a 3rd party dependency. In modern Erlang versions, the module offers at least a comparable feature set and efficiency of Lager. Users who relied on Lager-specific configuration, e.g. custom extensions or sinks, would have to rebuild them on top of the standard Erlang `logger` module. GitHub issue: Different Raft-based features now can have different defaults and settings, with more configurability coming at a later

For example, client ID tracking in the MQTT plugin can use settings for lower memory footprint and more frequent compaction while stream and quorum queues use settings more optimal for higher throughput on the same node. GitHub issue: Continuous integration of open source RabbitMQ has switched to Bazel, GitHub Actions and , resulting in much faster and incremental test runs. is a new project open sourced by the RabbitMQ Core team as a result. Process group membership now uses `pg`. GitHub issue: `powershell.exe` now can run without profile GitHub issue: Queue index recovery now can continue after a forced node shutdown during recovery (e.g. killed) GitHub issue: Correct an issue where the `num_acceptors.ssl` configuration value was applied incorrectly GitHub issue: Correct an issue where the `--tags` flag was ignored if `--description` was not specified in the `rabbitmqctl add_vhost` command automates provisioning, management, and operations of RabbitMQ clusters running on Kubernetes. makes it possible to define RabbitMQ resources (virtual hosts, users, permissions, topologies, policies, etc) as Kubernetes objects. Kubernetes mechanism no longer uses randomized delays to avoid the inherent race condition during . Instead it relies on an internal distributed locking mechanism available in modern Erlang releases. While randomized startup delay was reasonably effective at ensuring only one cluster was formed even during parallel node startup, it by definitely assumes that with some low probability more than one node can still start as seed nodes, and be joined by different groups of cluster peers. The locking mechanism does not have this downside. Now that RabbitMQ requires Erlang 23.2, the internal locking library becomes an option for peer discovery. `clusterformation.randomizedstartupdelayrange.min` and `clusterformation.randomizedstartupdelayrange.max` configuration keys will no longer have any effect. GitHub issue: now supports . In case it is not available, requests will fall back to the original metadata service endpoint. The v2 endpoint offers substantial security improvements and is one of the . Contributed by @thuandb (AWS). GitHub issue: Quorum queues now can be federated. GitHub issue: Management UI now honors queue name length limits GitHub issue: Management UI now sets a correct www-authenticate response header on authentication failures GitHub issue: cowboy has been upgraded from `2.6.1` to `2.8.0` cowlib has been upgraded from `2.7.0` to `2.9.1` lager has been removed jsx has been upgraded from `2.9.0` to `3.1.0` observer_cli has been upgraded from `1.5.2` to `1.6.2` osiris had been introduced at `0.1.0` prometheus has been upgraded from `4.6.0` to `4.8.1` ra has been upgraded from `1.1.9` to `2.0.0` ranch has been upgraded from `1.7.1` to `2.0.0` recon has been upgraded from `2.5.0` to `2.5.1` seshat had been introduced at `0.1.0` socat has been removed syslog has been upgraded from `3.4.5` to `4.0.0` systemd had been introduced at `0.6.1`