Update Event Exchange Plugin docs #2129
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This is the docs PR for rabbitmq/rabbitmq-server#12714 and applies to RabbitMQ >= 4.1 Note that the internal event types were documented previously at three different places: 1. https://github.com/rabbitmq/rabbitmq-server/blob/main/deps/rabbitmq_event_exchange/README.md 2. https://www.rabbitmq.com/docs/event-exchange 3. https://www.rabbitmq.com/docs/logging#internal-events All of them listed different and/or outdated event types. From now on, we use the 3rd place as only place and single source of truth for documenting internal events.
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## What? Prior to this commit, the `rabbitmq_event_exchange` internally published always AMQP 0.9.1 messages to the `amq.rabbitmq.event` topic exchange. This commit allows users to configure the plugin to publish AMQP 1.0 messages instead. ## Why? Prior to this commit, when an AMQP 1.0 client consumed events, event properties that are lists were omitted, for example property `client_properties` of event `connection.created` or property `arguments` of event `queue.created` because of the following sequence: 1. The event exchange plugins listens for all kind of internal events. 2. The event exchange plugin re-publishes all events as AMQP 0.9.1 message to the event exchange. 3. Later, when an AMQP 1.0 client consumes this message, the broker must translate the message from AMQP 0.9.1 to AMQP 1.0. 4. This translation follows the rules outlined in https://www.rabbitmq.com/docs/conversions#amqpl-amqp 5. Specifically, in this table the row before the last one describes the rule we're hitting here. It says that if the AMQP 0.9.1 header value is not an `x-` prefixed header and its value is an array or table, then this header is not converted. That's because AMQP 1.0 application-properties must be simple types as mandated in https://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#type-application-properties ## How? The user can configure the plugin as follows to have the plugin internally publish AMQP 1.0 messages: ``` event_exchange.protocol = amqp_1_0 ``` To support complex types such as lists, the plugin sets all event properties as message-annotations. The plugin prefixes all message annotation keys with `x-opt-` to comply with the AMQP 1.0 spec. ## Alternative Design An alternative design would have been to format all event properties e.g. as JSON within the message body. However, this breaks routing on specific event property values via a headers exchange. ## Documentation rabbitmq/rabbitmq-website#2129
ansd
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## What? Prior to this commit, the `rabbitmq_event_exchange` internally published always AMQP 0.9.1 messages to the `amq.rabbitmq.event` topic exchange. This commit allows users to configure the plugin to publish AMQP 1.0 messages instead. ## Why? Prior to this commit, when an AMQP 1.0 client consumed events, event properties that are lists were omitted. For example property `client_properties` of event `connection.created` or property `arguments` of event `queue.created` were omitted because of the following sequence: 1. The event exchange plugins listens for all kind of internal events. 2. The event exchange plugin re-publishes all events as AMQP 0.9.1 message to the event exchange. 3. Later, when an AMQP 1.0 client consumes this message, the broker must translate the message from AMQP 0.9.1 to AMQP 1.0. 4. This translation follows the rules outlined in https://www.rabbitmq.com/docs/conversions#amqpl-amqp 5. Specifically, in this table the row before the last one describes the rule we're hitting here. It says that if the AMQP 0.9.1 header value is not an `x-` prefixed header and its value is an array or table, then this header is not converted. That's because AMQP 1.0 application-properties must be simple types as mandated in https://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#type-application-properties ## How? The user can configure the plugin as follows to have the plugin internally publish AMQP 1.0 messages: ``` event_exchange.protocol = amqp_1_0 ``` To support complex types such as lists, the plugin sets all event properties as AMQP 1.0 message-annotations. The plugin prefixes all message annotation keys with `x-opt-` to comply with the AMQP 1.0 spec. ## Alternative Design An alternative design would have been to format all event properties e.g. as JSON within the message body. However, this breaks routing on specific event property values via a headers exchange. ## Documentation rabbitmq/rabbitmq-website#2129
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This is the docs PR for
rabbitmq/rabbitmq-server#12714 and applies to RabbitMQ >= 4.1
Note that the internal event types were documented previously at three different places:
All of them listed different and/or outdated event types. From now on, we use the 3rd place as only place and single source of truth for documenting internal events.