Re: [Kimchi-devel] [RFC] asynchronous (websocket based) notification (Wok #16)

On 02/13/2017 02:29 PM, Daniel Henrique Barboza wrote: > > > On 02/13/2017 12:47 PM, Aline Manera wrote: >> 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? > > Imagine that a single socket 'wokchannel' is created. The plug-ins would > need to register in this channel to see the incoming messages. Now, > imagine > a kimchi function "refreshVMsList" that would refresh the VMs in the > listing. > While in the Guest tab the function would work as intended. However, when > going to any other tab, "refreshVMList" will start to fail because > the elements > the function references will no longer exists. > > There is a Ginger bugs I've fixed in the past with this scenario: > https://github.com/kimchi-project/ginger/issues/482 . In this bug, the > ginger.getSensorsInput were being called out of the Administration > tab, causing > JS errors. > > The solution in this case would be to remove the listeners when > switching to > a new tab. Add the listener when the tab is created, remove it when it is > no longer needed. This is the exact same behavior I need to implement > with > the Websockets. > > Thus, I don't see any obvious gain or simplification by having only > one connection > and add/remove listeners versus one connection for each tab. > Hrm... I was thinking in something like: 1) The plugins would register a listener globally On wok.main.js: wok.notificationsListeners = {} On kimchi.main.js: wok.notificationsListeners['<code-to-list-vms>'] = <functions-to-list-vms> 2) Reuse the notifications listener we have today and use the "code" to proper treat it. Let's call it handleNotification() which will do { // One notification arrived // Gets its code and redirect to the proper listener func = wok.notificationsListeners.get(<code>) if func !== undefined // call func func(); } So that way, I don't think the plugins need to unregister a listener when switching tabs. Wok would proper gets the logic to do that avoiding errors.

> > Daniel > >> >>> I am planning to do a proof of concept of an UI working with this new >>> push server notifications in the 'User Log' tab, together with this >>> backend >>> work. When a new log entry is created, a push notification is sent >>> and the >>> UI would refresh automatically. This implementation would be used >>> as a base >>> for the other tabs/plug-ins. >>> >>> >>> Let me know what you think! >>> >>> >>> Daniel >>> >>> >>> PS: for the record, before deciding to use websockets I've >>> considered using SSE >>> (Server-side Events), a HTML5 standard, but gave up due to lack of >>> SSE support >>> from Microsoft browsers. >>> >>> >>> _______________________________________________ >>> Kimchi-devel mailing list >>> Kimchi-devel(a)ovirt.org >>> http://lists.ovirt.org/mailman/listinfo/kimchi-devel >> >