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From "Leo Neumeyer (Commented) (JIRA)" <>
Subject [jira] [Commented] (S4-22) Adaptor
Date Wed, 07 Dec 2011 23:00:40 GMT


Leo Neumeyer commented on S4-22:

I created an example of an App that exports events using EventSource. Consumer apps need to
subscribe to the event source and to start receiving the events.

* ClockApp: The producer app.
* ClockPE: Generates events of type ClockEvent at periodic intervals. The payload is the time.
* ClockEvent: The event type to be exported. (Consumer apps can get the time.)

Now other apps can start consuming without creating dependencies between apps at compile time.
The shared event needs to be known by all the apps. 

The Server class will need to get the Streamables using the App getter method: public List<Streamable<?
extends Event>> getStreams() and figure out which streamable needs to bind based on
the deployment descriptor.

NOTE: In this example I am using ClockEvent which is defined in ClockApp but it doesn't have
to be that way. To further reduce dependencies we can use a GenericEvent which we haven't
implemented yet. The Generic Event is in the S4 libraries so it can be easily shared by all
Does this make sense? Comments? Once we agree on this, we can move to the Adaptor discussion.


> Adaptor
> -------
>                 Key: S4-22
>                 URL:
>             Project: Apache S4
>          Issue Type: Improvement
>    Affects Versions: 0.5
>            Reporter: Leo Neumeyer
>            Assignee: Bruce Robbins
>             Fix For: 0.5
>         Attachments: s4-subclusters.pdf
> Need an adaptor for v0.5
> Idea I posted earlier:
> What do you think of this idea for a simple adaptor:
> - Adaptor extends App
> - Adaptor can send events but not receive (for now)
> - Adaptor is deployed as a regular App to the S4 cluster and as an
> Adaptor type  in a host (separate from the S4 cluster).
> - Adaptor, unlike regular apps, can accept event data (in any format)
> directly, not via comm layer.
> - Input data is transformed into S4 events using a modular approach
> and by providing standard modules such as JSON.
> - Output events are exposed using EventSource and consumed by other
> apps without even knowing that they are Adaptors (only the App type is
> exposed in the cluster).
> - S4 events can be processed locally using PEs and Streams as usual.
> (We kind of need to get a local Sender for the local PEs and a
> standard cluster Sender for the EventSource object.)
> So why this approach?
> The GOOD:
> - Seems to be the least disruptive way to inject external events
> - Apps can easily consume the events in a modular way without any
> dependencies. Getting events from an adaptor or from another app is
> identical.
> - The adaptor would be packaged and deployed to the cluster as if it
> was an App (no incremental cost)
> - The adaptor can do preprocessing using the same programming model
> and can reuse PEs.
> -  We need to also deploy the Adaptor in a separate host. On the other
> hand, this is inevitable. At least we use the same approach instead of
> creating a different system.
> -  The Adaptor will need to be integrated with ZK to get the physical addresses.
> -  We need to deal with two senders.
> for later: two-way communication and adapter clusters.
> thoughts?

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