RabbitMQ is a popular message broker (https://www.rabbitmq.com/). Azure functions support RabbitMQ triggers and bindings. In other words, azure function can listen to a RabbitMQ message queue and also possible to push a message to the RabbitMQ message queue.
Microsoft Documentation and sample C#
https://docs.microsoft.com/en-us/azure/azure-functions/functions-bindings-rabbitmq
