Flink’s RabbitMQ connector defines a Maven dependency on the
“RabbitMQ AMQP Java Client”, is triple-licensed under the Mozilla Public License 1.1 (“MPL”), the GNU General Public License version 2 (“GPL”) and the Apache License version 2 (“ASL”).
Flink itself neither reuses source code from the “RabbitMQ AMQP Java Client”
nor packages binaries from the “RabbitMQ AMQP Java Client”.
Users that create and publish derivative work based on Flink’s
RabbitMQ connector (thereby re-distributing the “RabbitMQ AMQP Java Client”)
must be aware that this may be subject to conditions declared in the Mozilla Public License 1.1 (“MPL”), the GNU General Public License version 2 (“GPL”) and the Apache License version 2 (“ASL”).
This connector provides access to data streams from RabbitMQ. To use this connector, add the following dependency to your project:
Note that the streaming connectors are currently not part of the binary distribution. See linking with them for cluster execution here.
Follow the instructions from the RabbitMQ download page. After the installation the server automatically starts, and the application connecting to RabbitMQ can be launched.
This connector provides a RMQSource class to consume messages from a RabbitMQ
queue. This source provides three different levels of guarantees, depending
on how it is configured with Flink:
Exactly-once: In order to achieve exactly-once guarantees with the
RabbitMQ source, the following is required -
Enable checkpointing: With checkpointing enabled, messages are only
acknowledged (hence, removed from the RabbitMQ queue) when checkpoints
Use correlation ids: Correlation ids are a RabbitMQ application feature.
You have to set it in the message properties when injecting messages into RabbitMQ.
The correlation id is used by the source to deduplicate any messages that
have been reprocessed when restoring from a checkpoint.
Non-parallel source: The source must be non-parallel (parallelism set
to 1) in order to achieve exactly-once. This limitation is mainly due to
RabbitMQ’s approach to dispatching messages from a single queue to multiple
At-least-once: When checkpointing is enabled, but correlation ids
are not used or the source is parallel, the source only provides at-least-once
No guarantee: If checkpointing isn’t enabled, the source does not
have any strong delivery guarantees. Under this setting, instead of
collaborating with Flink’s checkpointing, messages will be automatically
acknowledged once the source receives and processes them.
Below is a code example for setting up an exactly-once RabbitMQ source.
Inline comments explain which parts of the configuration can be ignored
for more relaxed guarantees.
Quality of Service (QoS) / Consumer Prefetch
The RabbitMQ Source provides a simple way to set the basicQos on the source’s channel through the RMQConnectionConfig.
Since there is one connection/ channel per-parallel source, this prefetch count will effectively be multiplied by the
source’s parallelism for how many total unacknowledged messages can be sent to the job at one time.
If more complex configuration is required, RMQSource#setupChannel(Connection) can be overridden and manually configured.
The prefetch count is unset by default, meaning the RabbitMQ server will send unlimited messages. In production, it
is best to set this value. For high volume queues and checkpointing enabled, some tuning may be required to reduce
wasted cycles, as messages are only acknowledged on checkpoints if enabled.
More about QoS and prefetch can be found here
and more about the options available in AMQP 0-9-1 here.
This connector provides a RMQSink class for sending messages to a RabbitMQ
queue. Below is a code example for setting up a RabbitMQ sink.