Event Dispatchers¶

Developing A New Event Dispatcher¶

The first step for adding a new dispatcher is to create a new file containing a subclass of EventBackend. In this new class, say JsonDispatcher, you will need to implement the dump() class method as examplified below:

class JsonDispatcher(base.EventBackend):
    """Dispatcher for dumping events to a JSON file."""

    @classmethod
    def dump(cls, level, action, **kwargs):
        # Your logic goes here
        ...

The level parameter for the method is identical to that defined by the logging module of Python. It is an integer representing the criticality of an event. The action parameter is an instance of Senlin action class, which is defined in the senlin.engine.actions.base module. There is virtually no constraints on which properties you will pick and how you want to process them.

Finally, the **kwargs parameter may provide some useful fields for you to use:

• timestamp: A datetime value that indicates when the event was generated.
• phase: A string value indicating the phase an action is in. Most of the time this can be safely ignored.
• reason: There are some rare cases where an event comes with a textual description. Most of the time, this is empty.
• extra: There are even rarer cases where an event comes with some additional fields for attention. This can be safely ignored most of the time.

Registering the New Dispatcher¶

For Senlin service to be aware of and thus to make use of the new dispatcher, you will register it to the Senlin engine service. This is done by editing the setup.cfg file in the root directory of the code base, for example:

[entry_points]
senlin.dispatchers =
    database = senlin.events.database:DBEvent
    message = senlin.events.message:MessageEvent
    jsonfile = <path to the dispatcher module>:<dispatch class name>

Finally, save that file and do a reinstall of the Senlin service, followed by a restart of the senlin-engine process.

$ sudo pip install -e .

Dynamically Enabling/Disabling a Dispatcher¶

All dispatchers are loaded when the Senlin engine is started, however, they can be dynamically enabled or disabled by editing the senlin.conf file. The option event_dispatchers in the [DEFAULT] section is a multi-string value option for this purpose. To enable your dispatcher (i.e. jsonfile), you will need to add the following line to the senlin.conf file:

event_dispatchers = jsonfile