Support exchange federation with MQTT 5.0 subscribers #13115
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## What? This commit fixes #13040. Prior to this commit, exchange federation crashed if the MQTT topic exchange (`amq.topic` by default) got federated and MQTT 5.0 clients subscribed on the downstream. That's because the federation plugin sends bindings from downstream to upstream via AMQP 0.9.1. However, binding arguments containing Erlang record `mqtt_subscription_opts` (henceforth binding args v1) cannot be encoded in AMQP 0.9.1. ## Why? Federating the MQTT topic exchange could be useful for warm standby use cases. ## How? This commit makes binding arguments a valid AMQP 0.9.1 table (henceforth binding args v2). Binding args v2 can only be used if all nodes support it. Hence binding args v2 comes with feature flag `rabbitmq_4.1.0`. Note that the AMQP over WebSocket [PR](#13071) already introduces this same feature flag. Although the feature flag subsystem supports plugins to define their own feature flags, and the MQTT plugin defined its own feature flags in the past, reusing feature flag `rabbitmq_4.1.0` is simpler. This commit also avoids database migrations for both Mnesia and Khepri if feature flag `rabbitmq_4.1.0` gets enabled. Instead, it's simpler to migrate binding args v1 to binding args v2 at MQTT connection establishment time if the feature flag is enabled. (If the feature flag is disabled at connection etablishment time, but gets enabled during the connection lifetime, the connection keeps using bindings args v1.) This commit adds two new suites: 1. `federation_SUITE` which tests that federating the MQTT topic exchange works, and 2. `feature_flag_SUITE` which tests the binding args migration from v1 to v2.
kjnilsson
approved these changes
Jan 22, 2025
|
The two CI checks fail for the same reason as in #13071 (comment) |
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What?
This commit fixes #13040.
Prior to this commit, exchange federation crashed if the MQTT topic exchange
(
amq.topicby default) got federated and MQTT 5.0 clients subscribed on thedownstream. That's because the federation plugin sends bindings from downstream
to upstream via AMQP 0.9.1. However, binding arguments containing Erlang record
mqtt_subscription_opts(henceforth binding args v1) cannot be encoded in AMQP 0.9.1.Why?
Federating the MQTT topic exchange could be useful for warm standby use cases.
How?
This commit makes binding arguments a valid AMQP 0.9.1 table (henceforth
binding args v2).
Binding args v2 can only be used if all nodes support it. Hence binding
args v2 comes with feature flag
rabbitmq_4.1.0. Note that the AMQPover WebSocket
PR already
introduces this same feature flag. Although the feature flag subsystem
supports plugins to define their own feature flags, and the MQTT plugin
defined its own feature flags in the past, reusing feature flag
rabbitmq_4.1.0is simpler.This commit also avoids database migrations for both Mnesia and Khepri
if feature flag
rabbitmq_4.1.0gets enabled. Instead, it's simpler tomigrate binding args v1 to binding args v2 at MQTT connection establishment
time if the feature flag is enabled. (If the feature flag is disabled at
connection etablishment time, but gets enabled during the connection
lifetime, the connection keeps using bindings args v1.)
This commit adds two new suites:
federation_SUITEwhich tests that federating the MQTT topicexchange works, and
feature_flag_SUITEwhich tests the binding args migration from v1 to v2