Synnefo

architecture and communication with a Ganeti backend is shown the below graph.

.. image:: images/cyclades-ganeti-communication.png

   :width: 50%

   :target: _images/cyclades-ganeti-communication.png

.. RabbitMQ

RabbitMQ Broker

---------------

Queue nodes run the RabbitMQ sofware, which provides AMQP functionality. To

guarantee high-availability, more than one Queue nodes should be deployed, each

of them belonging to the same `RabbitMQ cluster

<http://www.rabbitmq.com/clustering.html>`_. Synnefo uses RabbitMQ

active/active `High Available Queues <http://www.rabbitmq.com/ha.html>`_ that

are mirrored on nodes within a RabbitMQ cluster.

The RabbitMQ nodes that form the cluster, are declared to Synnefo through

the `AMQP_HOSTS` setting. Each time a Synnefo component needs to connect

RabbitMQ, one of this nodes is chosen in a random way. The client that

synnefo uses to connect with RabbitMQ, silently handles connection failures

and tries to reconnect to a different node. As long as one of these nodes

are up and running, functionality of synnefo should no be downgraded by

RabbitMQ node failures.

All the queues that are being used are declared as durable, meaning that

messages are persistently stored to RabbitMQ until are successfully processed

by a client.

Currently, RabbitMQ is used by the following components:

* snf-ganeti-eventd, snf-ganeti-hook and snf-progress-monitor:

  These components send messages concerning the status and progress of

  jobs in the Ganeti backend.

* snf-dispatcher: This daemon, consumes the messages that are send from

  the above components, and updates the Cyclades DB.

Installation

````````````

Please check RabbitMQ documentation which covers extensively the `installation

of RabbitMQ server <http://www.rabbitmq.com/download.html>`_ and the setup of a

`RabbitMQ cluster <http://www.rabbitmq.com/clustering.html>`_. Also, check out

the `web management plugin <http://www.rabbitmq.com/management.html>`_ that can

be useful for managing and monitoring RabbitMQ.

For a basic installation of RabbitMQ on two nodes (node1 and node2) you can do

the follow steps:

On both nodes, install rabbitmq-server and create a synnefo user:

.. code-block:: console

  $ apt-get install rabbitmq-server

  $ rabbitmqctl add_user synnefo "example_pass"

  $ rabbitmqctl set_permissions synnefo  ".*" ".*" ".*"

Also guarantee that two nodes share the same cookie, by running

.. code-block:: console

  $ scp node1:/var/lib/rabbitmq/.erlang.cookie node2:/var/lib/rabbitmq/.erlang.cookie

and restart the nodes:

.. code-block:: console

  $ /etc/init.d/rabbitmq-server restart

To setup the RabbitMQ cluster run:

.. code-block:: console

  root@node2: rabbitmqctl stop_app

  root@node2: rabbitmqctl reset

  root@node2: rabbitmqctl cluster rabbit@node1 rabbit@node2

  root@node2: rabbitmqctl start_app

You can verify that the cluster is set up correctly by running:

.. code-block:: console

  root@node2: rabbitmqctl cluster_status