Hi Daniel,
On 02/08/2017 05:07 PM, Daniel
Henrique Barboza wrote:
Hi everyone,
I want to start a discussion on https://github.com/kimchi-project/wok/issues/16,
"Asynchronous
event notification".
As most of you are aware, WoK does not have any sort of push
notification. WoK
UI works based on a polling strategy using the Notifications
API to fetch for any
backend notifications. This polling is on a 3 second interval
to not overload the server
with these requests. The problems with this approach are
obvious: the cost of
the polling process for both UI and backend, the interval for
a backend event to be
delivered to the UI and so forth.
- The idea
This work aims to implement an asynchronous strategy to
deliver server to client
messages. The idea is to use websockets* to establish a socket
connection between
the UI and the backend. The backend can send any message using
this socket and
the UI, after receiving it, can act upon immediately.
- Push server implementation
This socket in the backend side would act as a 'push server'
that will receive the
connections and push the same messages to all of them. Only
server to client
messages will be sent.
This push server can be implemented in two ways:
* from scratch
* using an external library
One library that seems to do this asynchronous socket
implementation is tornado
( https://github.com/tornadoweb/tornado
). It is present in all distros we support
and it has Apache 2.0 licensing. I'll experiment with it and
see if it helps. I am
opened to any other suggestion of libraries that can be used
in the push server
implementation. If no library is good enough for us, I'll have
to implement it from
scratch.
I am OK in using it as it is available for Fedora 25, Ubuntu
16.10, openSUSE 42.2 and centOS 7.
It would be good to confirm it is also available for Debian 8 as
Lucio is working to get the package into the official distro.
- WoK backend design
In WoK backend, my idea is to reuse the 'add_notification'
method from the
existing Notifications API. When adding a notification, fire a
message to the
push server and notify all the listeners too.
Could you elaborate more on that?
For example, in Kimchi, after adding/starting/deleting a VM we
will need to notify all the browsers sessions to update the data
in UI.
Or on Wok, after enabling/disabling a plugin.
How will that be done with the notifications API?
From the documentation, the notifications API is as below:
* **GET**: Retrieve the full description of the
Notification
* code: message
ID
* message: message text already
translated
* timestamp: first time notification was emitted
This approach has the following advantages:
- it will work out of the box for all backend messages in all
plug-ins that
uses the 'add_notification' method;
Today, the notifications API is only shown on UI as a warning
message to the user.
So I think much UI changes will be required.
- we can re-use the same JSON message format of
the Notifications API,
reducing the amount of UI work we'll have to adapt the
existing UIs;
Same I commented above.
- it will be harmless to implement. Given that
the push server will send
messages to all connected UI endpoints, if no endpoint is
connect
no message will be sent.
- WoK frontend design
For any tab that wants to receive the push notifications, just
connect
to the push server via websocket and react to the messages
sent - just
like it is done today with the notifications API but without
the need of
sending the GET /notifications messages.
We will need to be careful to not open unnecessary websockets
when
tab switching. We will need to pay attention to closing up the
connections
we don't need anymore.
Why do not open just one on Wok and reuse for all the plugins?