[Gluster-devel] Some updates on the eventing framework for Gluster

[Samikshan Bairagya]

Hi,

The updates for the eventing framework for gluster can be divided into 
the following two parts.

1. Bubbling out notifications through dbus signals from every gluster node.

* The 'glusterfs' module in storaged [1] exports objects on the system 
bus for every gluster volume. These objects hold the following properties:
- Name
- Id
- Status (0 = Created, 1 = Started, 2 = Stopped)
- Brickcount

* A singleton dbus object corresponding to glusterd is also exported by 
storaged on the system bus. This object holds properties to track the 
state of glusterd (LoadState and ActiveState).

2. Aggregating all these signals from each node over an entire cluster.

* Using Kafka [2] for messaging over a cluster: Implementing a (dbus 
signal) listener in python that converts these dbus signals from objects 
to 'keyed messages' in Kafka under a particular 'topic'.

For example, if a volume 'testvol' is started, a message is published 
under topic 'testvol', with 'status' as the 'key' and the changed status 
('1' in this case) as the 'value'.


*** Near term plans:
- Export dbus objects corresponding to bricks.
- Figure out how to map the path to the brick directory to the block 
device and consequently the drive object. The 'SmartFailing' property 
from org.storaged.Storaged.Drive.Ata [3] interface can then be used to 
track brick failures.
- Make the framework work over a multi-node cluster with possibly a 
multi-broker kafka setup to identify redundancies as well as to keep 
consistent information across the cluster.

Views/feedback/queries are welcome.

[1] https://github.com/samikshan/storaged/tree/glusterfs
[2] http://kafka.apache.org/documentation.html#introduction
[3] 
http://storaged-project.github.io/doc/latest/gdbus-org.storaged.Storaged.Drive.Ata.html#gdbus-property-org-storaged-Storaged-Drive-Ata.SmartFailing

Thanks and Regards,

Samikshan