Open Stack

We may also want to put in some kind version or self-documenting URL
so it's easier to accommodate message format changes later on.

As for the issue of things getting backed up in the queues for other
non-PuSH mechanisms (and fanout), burrow has fanout functionality
that depends on messages to expire (every message is inserted with
a TTL). This would allow multiple readers to see the same message
and for it to disappear after say an hour. This allows deployments,
third party tools, and clients to write workers to act on events from
the raw queue.

With burrow, it will also be possible for clients to pull raw messages
directly from the queue via a REST API in a secure fashion using
the same account credentials as other OpenStack service (whatever
keystone is configured for). So while an email notification will want
to strip any sensitive information, a direct queue client could see
more details.

-Eric

On Mon, May 09, 2011 at 10:20:04PM +0000, Matt Dietz wrote:
>    Hey guys,
>    Monsyne Dragon and myself are proposing an implementation for
>    notifications going forward. Currently my branch exists
>    under https://code.launchpad.net/~cerberus/nova/nova_notifications. you'll
>    see that's it been proposed for merge, but we're currently refactoring it
>    around changes proposed at the summit during the notifications discussion,
>    which you can see at http://etherpad.openstack.org/notifications
>    At the heart of the above branch is the idea that, because nova is about
>    compute, we get notifications away from Nova as quickly as possible. As
>    such, we've implemented a simple modular driver system which merely pushes
>    messages out. The two sample "drivers" are for pushing messages into
>    Rabbit, or doing nothing at all. There's been talk about adding Burrow as
>    a third possible driver, which I don't think would be an issue.
>    One of the proposals is to have priority levels for each notification.
>    What we're proposing is emulating the standard Python logging module and
>    providing levels like "WARN' and "CRITICAL" in the notification.
>    Additionally, the message format we're proposing will be a JSON dictionary
>    containing the following attributes:
>    publisher_id - the source worker_type.host of the message.
>    timestamp - the GMT timestamp the notification was sent at
>    event_type - the literal type of event (ex. Instance Creation)
>    priority - patterned after the enumeration of Python logging levels in
>                   the set (DEBUG, WARN, INFO, ERROR, CRITICAL)
>    payload - A python dictionary of attributes
>    Message example:
>        { 'publisher_id': 'compute.host1',
>          'timestamp': '2011-05-09 22:00:14.621831',
>          'priority': 'WARN',
>          'event_type': 'compute.create_instance',
>          'payload': {'instance_id': 12, ... }}
>    There was a lot of concern voiced over messages backing up in any of the
>    queueing implementations, as well as the intended priority of one message
>    over another. There are couple of immediately obvious solutions to this.
>    We think the simplest solution is to implement N queues, where N is equal
>    the number of priorities. Afterwards, consuming those queues is
>    implementation specific and dependent on the solution that works best for
>    the user.
>    The current plan for the Rackspace specific implementation is to use
>    PubSubHubBub, with a dedicated worker consuming the notification queues
>    and providing the glue necessary to work with a standard Hub
>    implementation. I have a very immature worker implementation
>    at https://github.com/Cerberus98/yagi if you're interested in checking
>    that out. 
>    We'll be going forward with this plan immediately, but we'd love feedback
>    if you have it. Questions, comments, concerns are very much welcomed!
>    Matt Dietz

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