Publish Subscribe

The Mirabelle Websocket server allows user to subscribe to the streams index or to channels.

An example

(streams
 (stream
  {:name :bar :default true}
  (where [:= :service "bar"]
    (index [:host])
    (publish! :my-channel))))

In this stream, we filter all events with :service “bar”. Then, we index them, and we also call publish! to publish the event to a channel named :my-channel.

A channel is created by default for each index. For the default index shared by all streams defined in the configuration, the name is default-index.

If you create a stream using the API, the channel will be <stream-name>-index.

Users can also subscribe to other channels, not related to indexes. It’s what publish! does. In this example, all users subscribing to the :my-channel channel will receive the events.

You can test that yourself by running the websocket.py script available here. You will need Python 3, and to install the dependencies listed in requirements.txt using pip install -r requirements.txt.

When you subscribe to a channel, you should provide a valid where clause in base64. For example, the query [:always-true] which matches everything would be WzphbHdheXMtdHJ1ZV0=.

You can now run the script with ./websocket.py. By default, it subscribes to the default index. You can specify a channel with --channel (like --channel my-channel here), or a query with --query (the query will be automatically converted to base64 by the script).

You can also write your own scripts in various languages. You need to subscribe to ws://<host>:<port>/channel/<channel-name>?query=<query>.

Riemann compatibility

In order to be compatible with Riemann clients, you can also subscribe on /index (to subscribe to the default index), or /index?stream=<stream-name> to subscribe to an index for a dynamic stream.