RabbitMq Driver Deployment Guide¶
Introduction¶
The RabbitMQ Driver is a messaging transport backend in oslo.messaging. The driver maps the base oslo.messaging capabilities for notification message exchange onto the RabbitMQ distributed message broker. More detail regarding the RabbitMQ server is available from the RabbitMQ website.
Abstract¶
The RabbitMQ Driver is a messaging transport backend supported in oslo.messaging. Communications between the driver and RabbitMQ server backend uses the AMQP 0-9-1 protocol (Advanced Message Queuing Protocol) which is an open application layer that allows clients applications to communicate with messaging middleware brokers in a standard way. AMQP defines all APIs to request messages from a message queue or to publishes messages to an exchange. The RabbitMQ driver integrates the kombu python client for full protocol support and utilizes the Producer API to publish notification messages and the Consumer API for notification listener subscriptions. The driver is able to work with a single instance of a RabbitMQ server or a clustered RabbitMQ server deployment.
Exchange¶
Exchange is a AMQP mechanism that it designed to dispatch the messages like a proxy wrapping.
Messages are always published to exchanges.
An exchange can:
receives messages from producers
push messages to queues
Exchanges can distribute message copies to one or many queues using rules called bindings.
AMQP protocol defines different types of exchanges:
direct
topic
headers
fanout
An exchange can live without any binding. By default, no exception is raised if the message is not redirected to any queue, unless the mandatory flag is used.
oslo.messaging allow you to send and consume messages in a related manner through the Connection class.
With mandatory flag RabbitMQ raises a callback if the message is not routed to any queue. This callback will be used to loop for a timeout and let’s a chance to sender to recover.
Queue¶
The AMQP queue is the messages store, it can store the messages in memory or persist the messages to the disk.
The queue is bound to the exchange through one or more bindings.
Consumers can consume messages from the queue.
Queues have names so that applications can reference them.
Queues have properties that define how they behave.
Routing-Key¶
The routing key is part of the AMQP envelop of the message. The routing key is set by the producer to route the sended message. When a message is received, the exchange will try to match the message routing-key with the binding key of all the queues bound to it. If no match exist the message will be ignored else the message will be routed to the corresponding queue who binding key is matched.
Exchange types¶
direct¶
A direct exchange is an exchange which route messages to queues based on message routing key. Message will be directly delivered to the queue that correspond to the routing-key. direct is a type of exchange so RabbitMQ backend does not store the data.
topic¶
The RabbitMQ topic is an exchange type. In RabbitMQ messages sent to a topic exchange can’t have an arbitrary routing_key - it must be a list of words, delimited by dots. The words can be anything, but usually they specify some features connected to the message. A few valid routing key examples: “blue.orange.yellow”, “cars.bikes”, “quick.orange.rabbit”. There can be as many words in the routing key as you like, up to the limit of 255 bytes.. In oslo.messaging, a notification listener subscribes to a topic in a supplied target that is directly mapped by the driver to the RabbitMQ topic.
fanout¶
The fanout exchange will broadcasts all messages it receives to all the queues it knows.
headers¶
An headers exchange will route messages to queues by using message header content instead of routing by using the routing key like described previously. In this case producer will adds message header values as key-value pair in and he will sends by using the headers exchange.
The exchange will try to match all or any (based on the value of “x-match”) header value of the received message with the binding value of all the queues bound to it.
The exchange will determine which header to use to match the binding queues by using the value of the “x-match” header entry.
If match is not found, the message will be ignored else it route the message to the queue whose binding value is matched.
Health check with heartbeat frames¶
The RabbitMQ driver of oslo.messaging allow you to detect dead TCP connections with heartbeats and TCP keepalives. The heartbeat function from the driver is build over the heartbeat_check feature of kombu client and over the AMQP 0.9.1 heartbeat feature implemented by RabbitMQ. Heartbeating is a technique designed to undo one of TCP/IP’s features, namely its ability to recover from abroken physical connection by closing only after a quite long time-out. In some scenarios we need to knowvery rapidly if a peer is disconnected or not responding for other reasons (e.g. it is looping). Since heart-beating can be done at a low level, AMQP 0.9.1 implement this as a special type of frame that peers exchange at the transport level, rather than as a class method. Heartbeats also defend against certain network equipment which may terminate “idle” TCP connections when there is no activity on them for a certain period of time. The driver will always run the heartbeat in a native python thread and avoid to inherit the execution model from the parent process to avoid to use green threads.
Prerequisites¶
In order to run the driver the kombu python client must be installed. The RabbitMQ driver integrates a Python client based on kombu and on py-amqp for full protocol support and utilizes the Producer API to publish notification messages and the Consumer API for notification listener subscriptions.
Source packages for the kombu library are available via PyPI. Since the RabbitMQ driver is not an optional extension to oslo.messaging these packages installed by default.
Configuration¶
Transport URL Enable¶
In oslo.messaging, the transport_url parameter defines the OpenStack service
backends for RPC and notifications. The URL is of the form:
transport://user:pass@host1:port[,hostN:portN]/virtual_host
Where the transport value specifies the RPC or notification backend as
one of amqp, rabbit, kafka, etc. To specify and enable the
RabbitMQ driver for notifications, in the section
[oslo_messaging_notifications] of the service configuration file,
specify the transport_url parameter:
[oslo_messaging_notifications]
transport_url = rabbit://username:password@kafkahostname:9092
Note, that if a transport_url parameter is not specified in the
[oslo_messaging_notifications] section, the [DEFAULT] transport_url
option will be used for both RPC and notifications backends.
Driver Options¶
It is recommended that the default configuration options provided by
the RabbitMQ driver be used. The configuration options can be modified
in the oslo_messaging_rabbit section of the service
configuration file.
