AMQP 1.0 Protocol Driver Deployment Guide¶

Direct Messaging¶

The RPC messaging pattern is a synchronous exchange between client and server that is temporally bracketed. The direct messaging capabilities provided by the message router are optimal for the RPC messaging pattern.

The driver can readily scale operation from working with a single instances of a message router to working with a large scale routed mesh interconnect topology.

Store and Forward¶

The Notification messaging pattern is an asynchronous exchange from a notifier to a listener (e.g. consumer). The listener need not be present when the notification is sent. Thus, the store and forwarding capabilities provided by the message broker are required for the Notification messaging pattern.

This driver is able to work with a single instance of a message broker or a clustered broker deployment.

It is recommended that the message router intermediary not be used for the Notification messaging pattern due to the consideration that notification messages will be dropped when there is no active consumer. The message router does not provide durability or store-and-forward capabilities for notification messages.

Hybrid Messaging Backends¶

Oslo.messaging provides a mechanism to configure separate backends for RPC and Notification communications. This is supported through the specification of separate RPC and Notification transport urls in the service configuration. This capability enables the optimal alignment of messaging patterns to messaging backend and allows for different messaging backend types to be deployed.

This document provides deployment and configuration information for use of this driver in hybrid messaging configurations.

Addressing¶

A new address syntax was added to the driver to support efficient direct message routing. This new syntax will also work with a broker intermediary backend but is not compatible with the address syntax previously used by the driver. In order to allow backward compatibility, the driver will attempt to identify the intermediary type for the backend in use and will automatically select the ‘legacy’ syntax for broker-based backends or the new ‘routable’ syntax for router-based backends. An address mode configuration option is provided to override this dynamic behavior and force the use of either the legacy or routable address syntax.

Message Acknowledgement¶

A primary functional difference between a router and a broker intermediary type is when message acknowledgement occurs.

The router does not “store” the message hence it does not generate an acknowledgement. Instead the consuming endpoint is responsible for message acknowledgement and the router forwards the acknowledgement back to the sender. This is known as ‘end-to-end’ acknowledgement. In contrast, a broker stores then forwards the message so that message acknowledgement is performed in two stages. In the first stage, a message acknowledgement occurs between the broker and the Sender. In the second stage, an acknowledgement occurs between the Server and the broker.

This difference affects how long the Sender waits for the message transfer to complete.

                                                      +dispatch+
                                                      |  (3)   |
                                                      |        |
                                                      |        v
+--------------+    (1)    +----------+    (2)     +--------------+
|    Client    |---------->|  Router  |----------->|    Server    |
|   (Sender)   |<----------| (Direct) |<-----------|  (Listener)  |
+--------------+    (5)    +----------+    (4)     +--------------+

For example when a router intermediary is used, the following sequence occurs:

1. The message is sent to the router
2. The router forwards the message to the Server
3. The Server dispatches the message to the application
4. The Server indicates the acknowledgement via the router
5. The router forwards the acknowledgement to the Sender

In this sequence, a Sender waits for the message acknowledgement until step (5) occurs.

                                                      +dispatch+
                                                      |  (4)   |
                                                      |        |
                                                      |        v
+--------------+    (1)    +----------+    (3)     +--------------+
|    Client    |---------->|  Broker  |----------->|    Server    |
|   (Sender)   |<----------| (Queue)  |<-----------|  (Listener)  |
+--------------+    (2)    +----------+    (5)     +--------------+

And when a broker intermediary is used, the following sequence occurs:

1. The message is sent to the broker
2. The broker stores the message and acknowledges the message to the Sender
3. The broker sends the message to the Server
4. The Server dispatches the message to the application
5. The Server indicates the acknowledgement to the broker

In this sequence, a Sender waits for the message acknowledgement until step (2) occurs.

Therefore the broker-based Sender receives the acknowledgement earlier in the transfer than the routed case. However in the brokered case receipt of the acknowledgement does not signify that the message has been (or will ever be) received by the Server.

Protocol Engine¶

This driver uses the Apache QPID Proton AMQP 1.0 protocol engine. This engine consists of a platform specific library and a python binding. The driver does not directly interface with the engine API, as the API is a very low-level interface to the AMQP protocol. Instead, the driver uses the pure python Pyngus client API, which is layered on top of the protocol engine.

In order to run the driver the Proton Python bindings, Proton library, Proton header files, and Pyngus must be installed. Pre-built packages for both Pyngus and the Proton protocol engine are available for various Linux distributions (see packages below). It is recommended to use the pre-built packages if they are available for your platform.

The Proton package includes a C extension that links to the Proton library. If this library is not installed, then the Proton install script will attempt to download the necessary Proton C source files from the Apache repository and build the library locally.

In order to build the Proton C source locally, there are a number of tools and libraries that need to be present:

• The tools and library necessary for Python development
• The SWIG wrapper generator
• The OpenSSL development libraries and headers
• The Cyrus SASL development libraries and headers

Note well: Currently the Proton Pypi package only supports building the C extension on Linux systems.

Router Intermediary¶

This driver supports a router intermediary that supports version 1.0 of the AMQP protocol. The direct messaging capabilities provided by this intermediary type are recommended for oslo.messaging RPC.

The driver has been tested with qpid-dispatch-router router in a devstack environment. The version of qpid-dispatch-router must be at least 0.7.0. The qpid-dispatch-router also uses the Proton engine for its AMQP 1.0 support, so the Proton library must be installed on the system hosting the qpid-dispatch-router daemon.

Pre-built packages for the router are available. See packages below.

Broker Intermediary¶

This driver supports a broker intermediary that supports version 1.0 of the AMQP protocol. The store and forward capabilities provided by this intermediary type are recommended for oslo.messaging Notifications.

The driver has been tested with the qpidd broker in a devstack environment. The version of qpidd must be at least 0.34. qpidd also uses the Proton engine for its AMQP 1.0 support, so the Proton library must be installed on the system hosting the qpidd daemon.

Pre-built packages for the broker are available. See packages below.

See the oslo specification for additional information regarding testing done on the driver.

Transport URL Enable¶

In oslo.messaging, the transport_url parameters define the OpenStack service backends for RPC and Notify. 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, zmq, etc.

To specify and enable the AMQP 1.0 driver for RPC, in the section [DEFAULT] of the service configuration file, specify the ‘transport_url’ parameter:

[DEFAULT]
transport_url = amqp://username:password@routerhostname:5672

To specify and enable the AMQP 1.0 driver for Notify, in the section [NOTIFICATIONS] of the service configuration file, specify the ‘transport_url’ parameter:

[NOTIFICATIONS]
transport_url = amqp://username:password@brokerhostname:5672

Note, that if a ‘transport_url’ parameter is not specified in the [NOTIFICATIONS] section, the [DEFAULT] transport_url will be used for both RPC and Notify backends.

Driver Options¶

It is recommended that the default configuration options provided by the AMQP 1.0 driver be used. The configuration options can be modified in the oslo_messaging_amqp section of the service configuration file.

qpid-dispatch-router¶

First, verify that the Proton library has been installed and is imported by the qpid-dispatch-router intermediary. This can be checked by running:

$ qdrouterd --help

and looking for references to qpid-dispatch include and config path options in the help text. If no qpid-dispatch information is listed, verify that the Proton libraries are installed and that the version of the qdrouterd is greater than or equal to 0.6.0.

Second, configure the address patterns used by the driver. This is done by adding the following to /etc/qpid-dispatch/qdrouterd.conf.

If the legacy syntax for the addressing mode is required, include the following:

address {
    prefix: unicast
    distribution: closest
}

address {
    prefix: exclusive
    distribution: closest
}

address {
    prefix: broadcast
    distribution: multicast
}

For the routable syntax addressing mode, include the following:

address {
    prefix: openstack.org/om/rpc/multicast
    distribution: multicast
}

address {
    prefix: openstack.org/om/rpc/unicast
    distribution: closest
}

address {
    prefix: openstack.org/om/rpc/anycast
    distribution: balanced
}

address {
    prefix: openstack.org/om/notify/multicast
    distribution: multicast
}

address {
    prefix: openstack.org/om/notify/unicast
    distribution: closest
}

address {
    prefix: openstack.org/om/notify/anycast
    distribution: balanced
}

Note well: For any customization of the address mode and syntax used, it is required that the address entity configurations in the /etc/qpid-dispatch/qdrouterd.conf be updated.

qpidd¶

First, verify that the Proton library has been installed and is imported by the qpidd broker. This can checked by running:

$ qpidd --help

and looking for the AMQP 1.0 options in the help text. If no AMQP 1.0 options are listed, verify that the Proton libraries are installed and that the version of qpidd is greater than or equal to 0.34.

Second, configure the default address patterns used by the driver for a broker-based backend. This is done by adding the following to /etc/qpid/qpidd.conf:

queue-patterns=exclusive
queue-patterns=unicast
topic-patterns=broadcast

These patterns, exclusive, unicast, and broadcast are the legacy addressing values used by the driver. These can be overridden via the driver configuration options if desired (see above). If manually overridden, update the qpidd.conf values to match.

PyPi¶

Packages for Pyngus pypi and the Proton pypi engine are available on Pypi.

RHEL and Fedora¶

Packages exist in EPEL for RHEL/Centos 7, and Fedora 26+. Unfortunately, RHEL/Centos 6 base packages include a very old version of qpidd that does not support AMQP 1.0. EPEL’s policy does not allow a newer version of qpidd for RHEL/Centos 6.

The following packages must be installed on the system running the intermediary daemon:

qpidd daemon:

• qpid-cpp-server (version 0.26+)
• qpid-proton-c

The following packages must be installed on the systems running the services that use the new driver:

• Proton libraries: qpid-proton-c-devel
• Proton python bindings: python-qpid-proton
• pyngus (via Pypi)

Debian and Ubuntu¶

Packages for the Proton library, headers, and Python bindings are available in the Debian/Testing repository. Proton packages are not yet available in the Ubuntu repository. The version of qpidd on both platforms is too old and does not support AMQP 1.0.

Until the proper package version arrive the latest packages can be pulled from the Apache Qpid PPA on Launchpad:

sudo add-apt-repository ppa:qpid/released

The following packages must be installed on the system running the qdrouterd daemon:

• qdrouterd (version 0.8.0+)

The following packages must be installed on the system running the qpidd daemon:

• qpidd (version 0.34+)

The following packages must be installed on the systems running the services that use the new driver:

• Proton libraries: libqpid-proton2-dev
• Proton python bindings: python-qpid-proton
• pyngus (via Pypi)