I'm developing an Angular 4 app that connects to a REST API developed in NodeJS/Express/MySQL. I'm looking for a way to notify any connected clients when there is a change in the database, so they reload their datasets. I've done some searches on Google but I don't know the technical term of what I'm looking for, so I didn't find anything useful.
Can someone point me some resource on this subject? Thanks!
You have two options avaliable
1)HTML5 serversent events
A server-sent event is when a web page automatically gets updates from
a server.
https://www.w3schools.com/html/html5_serversentevents.asp
2)Socket.io
https://socket.io/
Based on my experience for simple realtime updates HTML5 server sent is enough
If you want to visualize changes "live", you should try websockets.
With websockets you could notify any client about any upcoming changes in data, think of it as some kind of chat between server and clients.
There's socket.io for Node.js developers and plenty of tutorials about how to set it up and get it running.
Thanks!
Time to learn some new things... I think I'll start with HTML5 Server Send Events, I think it'll be more than enough for what I need.
Cheers,
Related
I have an Express js server that supplies weather forecast information to its clients. Right now, it's basically an RPC API where the client (a python client in this case) requests different types of weather info from different endpoints. This is fine for right now, but I was thinking about implementing a subscription model. Rather than connecting to different endpoints for different information, the client could just subscribe for the info that it wants and the server would send it every so often (obviously configurable by the client).
Is there a way to do this with express? Would I have to set up a server on the client side as well to listen for the publish events?
A very good option is RabbitMQ, it's used for that right purpose.
I tried to find a good tutorial for you as a reference, however, I only find one in portuguese, but if you search around google you will find others in english.
But it's very simple, just like you want, you publish to the queue on some topic and have other clients subscribing that topic and processing the messages
Here is the link
https://medium.com/#programadriano/rabbitmq-publish-subscribe-com-node-js-9363848f58fe
Most examples I have seen are are just small demo's and not full stack applications and they use websocket for messaging, but for any chat application there is more data then just messages...suppose like user profile, his contacts etc.
So should I use websockets for all communication between server and client or just use them for sending messages and do other things through http? If I am to use websocket for all communication how do url design of the app...since websockets don't have have any different urls like http.
You might be interested in WAMP, an officially registered WebSocket subprotocol that provides applications with WebSocket based
asynchronous, bidirectional remote procedure calls
real-time publish & subscribe notifications
Disclaimer: I am original author of WAMP and work for Tavendo.
Pretty sure you'll get the usual "it depends" answer, because, well, it depends!
If you are going to build a large application, to be used by a number of different clients in different network arrangements etc then I personally wouldn't recommend using WebSockets for everything. Why?
It's a new standard, so not all clients support it
In some network configurations WebSocket traffic may be filtered out, meaning you end up with no communications - not great
If you end up exposing an external API then HTTP is much better fitted for the job and will likely be easier to code against. There are a lot more tools out there to help you with it and styles that everyone is familiar with, like REST, to follow.
Use WebSockets when you require data being pushed from the server without the client having to poll for it, or when HTTP header overhead becomes a problem. And if you still decide to use it make sure you have a fallback mechanism (e.g. longpolling) so you don't end up with no comms.
I'm afraid I can't help you regarding WebSocket API design... given it's a new standard I don't believe the community has settled on anything just yet so you'll have to come out with your own message-based scheme.
I want to monitor in real time the data that users enter in comments table.
I have an Apache server running, and suppose that has a node server on port 1337.
How would I do that every time someone save new data, eg return me the total number of table rows in comment and show it in a view?
Maybe way is to make the $this->Comment->save($this->request->data); using a different port using Httpsockect?
Yes, it is possible.
You have multiple ways of solving this, let me give you my ideas
You can simply use long-polling and don't use Node.js at all. It's a suitable solution if there won't be too much traffic there, otherwise you will have a bad time.
You can use websockets and don't use Node.js at all. Here you have a basic guide about websockets and PHP. Although, I am almost sure you won't be able to create "rooms", that is, sending notifications for specific comments.
You can also use Ratchet. This is a more sophisticated library to handle websockets and it supports rooms.
Lastly, if you want to full dive in with Node.js and CakePHP, I would suggest start by watching this talk given on Cakefest 2012 which exactly describe your scenario.
After you have watched that, you might want to learn a little about Socket.io. This is a more complex solution, but it's what I have used when integrating CakePHP and Node.js to create real time applications.
The strategy here is to have the users join a room when they visit /article/view/123, let's say the room name is the articleID, then socket.io will be listening for events happening in this room.
You will have a Cakephp method that handles the save. Then, when user submits the form you don't call directly the Cake action, you have socket.io to dispatch an event, then in your event you pass the data to the server (Node.js) and nodejs will call your cakephp function that saves the data. When Nodejs receives confirmation from CakePHP then you broadcast an event (using socket.io), this event will let know all users connected to that room that a comment has been made.
You have basically the choice between Websockets and long polling.
Websockets (with Ratchet and Autobahn.js)
Long Polling Using Comet
Decide which technology you want to use and start implementing your use case. Consider that Websockets are more or less new. Depending on your requirements you might not be able to use Websockets because you might have to support crappy browsers. See this page.
I am looking to build an web application using node.js and possibly socket.io but I am having a lots of confusion regarding whether to use socket.io or go with plain http. In the app the node.js server will be basically an api server which serves json to the javascript client or may be mobile clients too. The web app will also has chat messeneger for its users, this is where socket.io comes in.
I am not sure whether to use socket.io for the whole app or only for the chat part. Although my app itself could benefit from socket.io but its nothing that I think can't be done using plain http and client making more requests to the server.
I have read at several places that sometimes socket.io can be difficult to scale for more users.
Socket.io often crashes and specially creates probs when there are firewall in clients system.
More importantly.....I checked out socket.io user list and did not find many users, so was curious to know what kind of platform is more know chat network like facebook messenger, google talk etc are built upon, Are any built using http-ajax and continues querying to the server.
Please help me out in solving this question. Some might argue that this is a opinion based question. But what actually I am trying to figure out the implementation of socket.io and its limitation.
I would suggest serving your API over HTTP and leave the real-time business to Socket.io. If you are adverse to using Websockets, like #GeoPheonix stated, you can choose from a variety of transport methods using both socket.io and sockjs (https://github.com/sockjs/sockjs-node).
As far as scaling is concerned, I deployed a socket.io based real-time analytics/tracking service for a very large application with ana average of 400+ concurrent connections with no visible performance impact, but this may depend on the implementation and hardware.
Socket.io is faster than plain http. I recommend you to use it for all since you have to have a chat in first place.
In my case, real-time Texas Hold'em-like game can receive up to 2500 concurrent with one node process. However, if you change transport from websocket to xhr-polling, It can receive like more 10x than pure websocket. Your application is just chat so, I guess a little slow down wouldn't be a problem. If you sure you will exceed this number, yes, scale socket.io is a pain.
This problem will happen only if you open socket.io for port other than 80 and 443. If you have frontend web server with other language already, you can still use socket.io on another subdomain to be able to run on port 80 without conflict with your main frontend web server. Socket.io support cross-domain without a problem.
Have you used trello.com? If not, try it :). It's best for task management or even some Agile thing. They used socket.io. https://c9.io/ is another one. It's online IDE with google doc-like collaborative. One thing to note is xhr-polling trasport in socket.io is the same with http-ajax with long-polling (Better than general ajax). You can read more info at:
http://book.mixu.net/node/ch13.html
Brief Description:
Well, since many days I've been looking for an answer to this question but there seems to be answers for 'How to create a Push Notification Server' and like questions. I am using node.js and it's quite easy to 'create' a push notification server using sock.js (I've heard socket.io isn't good as compared to sock.js). No problem till here. But what I want is how to model such a server.
Details:
OK, so, let's say I've an application where there's a chat service (just an example this is, actual thing is big as you might have guessed). A person sends a message in a room and all the people in the room get notified. But what I want is a 'stateful' chat - that is, I want to store the messages in a data store. Here's where the trouble comes. Storing the message in the database and later telling everyone that "Hey, there's a message for you". This seems easy when we need the real-time activity for just one part of the app. What to do when the whole app is based on real-time communication? Besides this, I also want to have a RESTful api.
My solution (with which I am not really happy)
What I thought of doing was this: (on the server side of course)
Data Store
||
Data Layer (which talks to data store)
||
------------------
| |
Real-Time Server Restful server
And here, the Real-time server listens to interesting events that the data-layer publishes. Whenever something interesting happens, the server notifies the client. But which client? - This is the problem with my method
Hope you can be of help. :)
UPDATE:
I think I forgot to emphasize an important part of my question. How to implement a pub-sub system? (NOTE: I don't want the actual code, I'll manage that myself; just how to go about doing it is where I need some help). The problem is that I get quite boggled when writing the code - what to do how (my confusion is quite apparent from this question itself). Could please provide some references to read or some advice as to how to begin with this thing?
I am not sure if I understood you correctly; but I will summarize how I read it:
We have a real-time chat server that uses socket connections to publish new messages to all connected clients.
We have a database where we want to keep chat logs.
We have also a restful interface to access the realtime server to get current chats in a lazier manner.
And you want to architect your system this way:
In the above diagram, the components I circled with purple curve wants to be updated like all other clients. Am I right? I don't know what you meant with "Data Layer" but I thought it is a daemon that will be writing to database and also interfacing database for other components.
In this architecture, everything is okay in the direction you meant. I mean DataStore is connected by servers to access data, maybe to query client credentials for authentication, maybe to read user preferences etc.
For your other expectation from these components, I mean to allow these components to be updated like connected clients, why don't you allow them to be clients, too?
Your realtime server is a server for clients; but it is also a client for data layer, or database server, if we prefer a more common naming. So we already know that there is nothing that stops a server from being a client. Then, why can't our database system and restful system also be clients? Connect them to realtime server the same way you connect browsers and other clients. Let them enjoy being one of the people. :)
I hope I did not understand everything completely wrong and this makes sense for the question.