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<div class="moz-cite-prefix">On 02/13/2017 02:29 PM, Daniel Henrique
Barboza wrote:<br>
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cite="mid:373551a4-2764-9a27-3856-cb36c9682964@gmail.com"
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<div class="moz-cite-prefix">On 02/13/2017 12:47 PM, Aline Manera
wrote:<br>
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cite="mid:61da2e28-228b-92b0-2a9d-d1597f46fbad@linux.vnet.ibm.com"
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Hi Daniel,<br>
<br>
<div class="moz-cite-prefix">On 02/08/2017 05:07 PM, Daniel
Henrique Barboza wrote:<br>
</div>
<blockquote
cite="mid:2bf265f6-8c40-4517-0776-191d8dcdc2d3@gmail.com"
type="cite">
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Hi everyone,<br>
<br>
I want to start a discussion on <a moz-do-not-send="true"
class="moz-txt-link-freetext"
href="https://github.com/kimchi-project/wok/issues/16">https://github.com/kimchi-project/wok/issues/16</a>,<br>
"<span class="js-issue-title" style="box-sizing: border-box;">Asynchronous
event notification".<br>
<br>
As most of you are aware, WoK does not have any sort of push
notification. WoK<br>
UI works based on a polling strategy using the Notifications
API to fetch for any<br>
backend notifications. This polling is on a 3 second
interval to not overload the server<br>
with these requests. The problems with this approach are
obvious: the cost of<br>
the polling process for both UI and backend, the interval
for a backend event to be<br>
delivered to the UI and so forth.<br>
<br>
- The idea<br>
<br>
This work aims to implement an asynchronous strategy to
deliver server to client<br>
messages. The idea is to use websockets* to establish a
socket connection between<br>
the UI and the backend. The backend can send any message
using this socket and<br>
the UI, after receiving it, can act upon immediately.<br>
<br>
<br>
- Push server implementation<br>
<br>
This socket in the backend side would act as a 'push server'
that will receive the<br>
connections and push the same messages to all of them. Only
server to client<br>
messages will be sent. <br>
<br>
This push server can be implemented in two ways:<br>
<br>
* from scratch<br>
<br>
* using an external library<br>
<br>
One library that seems to do this asynchronous socket
implementation is tornado<br>
( <a moz-do-not-send="true" class="moz-txt-link-freetext"
href="https://github.com/tornadoweb/tornado">https://github.com/tornadoweb/tornado</a>
). It is present in all distros we support<br>
and it has Apache 2.0 licensing. I'll experiment with it and
see if it helps. I am<br>
opened to any other suggestion of libraries that can be used
in the push server<br>
implementation. If no library is good enough for us, I'll
have to implement it from<br>
scratch.<br>
<br>
</span></blockquote>
<br>
I am OK in using it as it is available for Fedora 25, Ubuntu
16.10, openSUSE 42.2 and centOS 7.<br>
<br>
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.<br>
<br>
<blockquote
cite="mid:2bf265f6-8c40-4517-0776-191d8dcdc2d3@gmail.com"
type="cite"><span class="js-issue-title" style="box-sizing:
border-box;"> <br>
- WoK backend design<br>
<br>
In WoK backend, my idea is to reuse the 'add_notification'
method from the<br>
existing Notifications API. When adding a notification, fire
a message to the<br>
push server and notify all the listeners too.<br>
<br>
</span></blockquote>
<br>
Could you elaborate more on that?<br>
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.<br>
Or on Wok, after enabling/disabling a plugin.<br>
<br>
How will that be done with the notifications API?<br>
<br>
From the documentation, the notifications API is as below:<br>
<br>
* **GET**: Retrieve the full description of the
Notification <br>
* code: message
ID <br>
* message: message text already
translated <br>
* timestamp: first time notification was emitted <br>
<br>
<blockquote
cite="mid:2bf265f6-8c40-4517-0776-191d8dcdc2d3@gmail.com"
type="cite"><span class="js-issue-title" style="box-sizing:
border-box;"> This approach has the following advantages:<br>
<br>
- it will work out of the box for all backend messages in
all plug-ins that<br>
uses the 'add_notification' method;<br>
<br>
</span></blockquote>
<br>
Today, the notifications API is only shown on UI as a warning
message to the user.<br>
So I think much UI changes will be required.<br>
<br>
<blockquote
cite="mid:2bf265f6-8c40-4517-0776-191d8dcdc2d3@gmail.com"
type="cite"><span class="js-issue-title" style="box-sizing:
border-box;"> - we can re-use the same JSON message format
of the Notifications API,<br>
reducing the amount of UI work we'll have to adapt the
existing UIs;<br>
<br>
</span></blockquote>
<br>
Same I commented above.<br>
<br>
<blockquote
cite="mid:2bf265f6-8c40-4517-0776-191d8dcdc2d3@gmail.com"
type="cite"><span class="js-issue-title" style="box-sizing:
border-box;"> - it will be harmless to implement. Given that
the push server will send<br>
messages to all connected UI endpoints, if no endpoint is
connect<br>
no message will be sent.<br>
<br>
<br>
- WoK frontend design<br>
<br>
For any tab that wants to receive the push notifications,
just connect<br>
to the push server via websocket and react to the messages
sent - just<br>
like it is done today with the notifications API but without
the need of<br>
sending the GET /notifications messages.<br>
<br>
We will need to be careful to not open unnecessary
websockets when<br>
tab switching. We will need to pay attention to closing up
the connections<br>
we don't need anymore.<br>
<br>
</span></blockquote>
<br>
Why do not open just one on Wok and reuse for all the plugins?<br>
</blockquote>
<br>
Imagine that a single socket 'wokchannel' is created. The plug-ins
would<br>
need to register in this channel to see the incoming messages.
Now, imagine<br>
a kimchi function "refreshVMsList" that would refresh the VMs in
the listing.<br>
While in the Guest tab the function would work as intended.
However, when<br>
going to any other tab, "refreshVMList" will start to fail because
the elements<br>
the function references will no longer exists.<br>
<br>
There is a Ginger bugs I've fixed in the past with this scenario:<br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="https://github.com/kimchi-project/ginger/issues/482">https://github.com/kimchi-project/ginger/issues/482</a>
. In this bug, the<br>
ginger.getSensorsInput were being called out of the Administration
tab, causing<br>
JS errors.<br>
<br>
The solution in this case would be to remove the listeners when
switching to<br>
a new tab. Add the listener when the tab is created, remove it
when it is<br>
no longer needed. This is the exact same behavior I need to
implement with<br>
the Websockets.<br>
<br>
Thus, I don't see any obvious gain or simplification by having
only one connection<br>
and add/remove listeners versus one connection for each tab.<br>
<br>
</blockquote>
<br>
Hrm... I was thinking in something like:<br>
<br>
1) The plugins would register a listener globally <br>
<br>
On wok.main.js:<br>
<br>
wok.notificationsListeners = {}<br>
<br>
On kimchi.main.js:<br>
<br>
wok.notificationsListeners['<code-to-list-vms>'] =
<functions-to-list-vms><br>
<br>
2) Reuse the notifications listener we have today and use the "code"
to proper treat it.<br>
<br>
Let's call it handleNotification() which will do<br>
<br>
{<br>
// One notification arrived<br>
// Gets its code and redirect to the proper listener<br>
func = wok.notificationsListeners.get(<code>)<br>
if func !== undefined<br>
// call func<br>
func();<br>
}<br>
<br>
So that way, I don't think the plugins need to unregister a listener
when switching tabs.<br>
Wok would proper gets the logic to do that avoiding errors.<br>
<br>
<blockquote
cite="mid:373551a4-2764-9a27-3856-cb36c9682964@gmail.com"
type="cite"> <br>
Daniel<br>
<br>
<blockquote
cite="mid:61da2e28-228b-92b0-2a9d-d1597f46fbad@linux.vnet.ibm.com"
type="cite"> <br>
<blockquote
cite="mid:2bf265f6-8c40-4517-0776-191d8dcdc2d3@gmail.com"
type="cite"><span class="js-issue-title" style="box-sizing:
border-box;"> I am planning to do a proof of concept of an
UI working with this new<br>
push server notifications in the 'User Log' tab, together
with this backend<br>
work. When a new log entry is created, a push notification
is sent and the<br>
UI would refresh automatically. This implementation would be
used as a base<br>
for the other tabs/plug-ins.<br>
<br>
<br>
Let me know what you think!<br>
<br>
<br>
Daniel<br>
<br>
<br>
PS: for the record, before deciding to use websockets I've
considered using SSE<br>
(Server-side Events), a HTML5 standard, but gave up due to
lack of SSE support<br>
from Microsoft browsers.<br>
</span> <br>
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