I have a Java Spring Application with a Tomcat server that listen on kafka topic. I want to display all messages in a real-time mode on the web page. Therefore, when a kafka messages is arrived in the backend I want to see it on my web page. I don't know a good approach to push kafka message directly to the front-end and display it on web page. Is someone could help my with a solution and some examples that could help? Thanks!
I have implemented a system like this in Java for my last employer, albeit not with Spring/Tomcat. It was consuming messages from Kafka and serving them on a web socket to be displayed in the browser. The approach I followed was to use akka-stream-kafka and akka-http for web-socket support. The benefit of that is both are based on akka-streams which makes it an easy fit for streaming data.
While you can embed akka-http in your spring app running inside tomcat, it may not feel the most natural choice any more as spring framework already has its own support for both kafka and websockets. However, if you're not familiar with either, then jumping on the akka approach may be easiest and the core logic goes along these lines (I can't share the code from work so have just put this together from the examples in the docs, not tested):
public Route createRoute(ActorSystem system) {
return path("ws", () -> {
ConsumerSettings<byte[], String> consumerSettings = ConsumerSettings.create(system, new ByteArrayDeserializer(), new StringDeserializer())
.withBootstrapServers("localhost:9092")
.withGroupId(UUID.randomUUID().toString()) //this is so that each client gets all messages. To be able to resume from where a client left off in case of disconnects, you can generate in on the client side and pass in the request
.withProperty(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest")
return handleWebSocketMessages(
Flow.fromSinkAndSourceCoupled(
Sink.ignore(),
Consumer.committableSource(consumerSettings, Subscriptions.topics("topic1"))
.map(msg -> TextMessage.create(msg.record().value()))
)
);
}
}
To expose this route you can follow the minimalistic example, the only difference being the route you define needs the ActorSystem:
final Http http = Http.get(system);
final ActorMaterializer materializer = ActorMaterializer.create(system);
final Flow<HttpRequest, HttpResponse, NotUsed> routeFlow = createRoute(system).flow(system, materializer);
final CompletionStage<ServerBinding> binding = http.bindAndHandle(routeFlow,
ConnectHttp.toHost("localhost", 8080), materializer);
Once you have your messages published to the websocket, the front end will code will of course depend on your UI framework of choice, the simplest code to consume ws messages from javascript is:
this.connection = new WebSocket('ws://url-to-your-ws-endpoint');
this.connection.onmessage = evt => {
// display the message
To easily display the message in the UI, you want the format to be something convenient, like JSON. If your Kafka messages are not JSON already, that's where the Deserializers in the first snippet come in, you can convert it to a convenient JSON string in the Deserializer or do it later on in the .map() called on the Source object.
Alternatively, if polling is an option you can also consider using the off-the-shelf Kafka Rest Proxy, then you only need to build the front-end.
Zup coders. I've implemented a simple website that uses Web Sockets PHP (Consik Yii2 solution: https://github.com/consik/yii2-websocket) vs JS (Html5).
Everything is working fine, I only have one issue with my solution, making sure the server is always alive.
I though about saving the WebSocket Instance into Cache and throw a cron that checks the state of the instance. I installed memcached and found out that i can´t save a serialized version of the WebSocket Server instance. ¿Is this a good solution? ¿Would Redis Caché fix this?
I also thought about using client side JS to react to "Error during WebSocket handshake: Unexpected response code: 200" but i can't seem to get it working. I also don't like making the URL that starts websockets public.
Ex:
connect = function(){
websocket = new WebSocket(webSocketURL);
websocket.onerror = function(){
$.get( "/startWebSocketServer",
function(data){
connect();
}
);
};
};
connect();
Thanks!
I think that as matter of fact you need a process supervisor who takes care to "supervise" your server process and do actions in response of process/system events like crash, restart etc..
There are several solutions for each case (standard OS implementations, personal preferences, fit your need), here a list http://without-systemd.org/wiki/index.php/Init , Service managers section could best fit your needs.
Supervisord is easy to setup and configure, it could be a good start thanks to a good bunch of examples around the net.
Solution 1: using a cache could not be the most orthodox way to implement a custom-made supervisor.
Solution 2: is legit as long as it informs user about a problem, the call to an exposed endpoint to start a service IMHO could be a security flaw.
I have a node server which is connecting to CloudMQTT and receiving messages in app.js. I have my client web app running on the same node server and want to display my messages received in app.js elsewhere in a .ejs file, I'm struggling as to how best to do this.
app.js
// Create a MQTT Client
var mqtt = require('mqtt');
// Create a client connection to CloudMQTT for live data
var client = mqtt.connect('xxxxxxxxxxx', {
username: 'xxxxx',
password: 'xxxxxxx'
});
client.on('connect', function() { // When connected
console.log("Connected to CloudMQTT");
// Subscribe to the temperature
client.subscribe('Motion', function() {
// When a message arrives, do something with it
client.on('message', function(topic, message, packet) {
// ** Need to pass message out **
});
});
});
Basically you need a way for the client (browser code with EJS - HTML, CSS and JS) to receive live updates. There are basically two ways to do this from the client to the node service:
A websocket session instantiated by the client.
A polling approach.
What's the difference?
Under the hood, a websocket is full-duplex communication mechanism. That means that you can open a socket from the client (browser) to the node server and they can talk to each other both ways over a long-lived session. The pro is that updates are often times instantaneous without having to incur the cost of making another HTTP request as in the polling case. The con is that it uses a socket connection that may be long-lived, and there is typically a socket pool on any server that has limited ability to deal with many sockets. There are ways to scale around this issue, but if it's a big concern for you, you may want to go with polling.
Polling is where you set up an endpoint on your server that the client JS code hits every now and then. That endpoint will return you the updated information. The con is that you are now making a new request in order to get updates, which may not be desirable if a lot of updates are expected to come through and the app is expected to be updated in the timeliest manner possible (most of the time polling is sufficient though). The pro is that you do not have a live connection open on the server indefinitely.
Again, there are many more pros and cons, these are just the obvious ones. You decide how to implement it. When the client receives the data from either of these mechanisms, you may update the UI in any suitable manner.
From the server end, you will need a way to persist the information coming from CloudMQTT. There are multiple ways to do this. If you do not care about memory consumption and are ok with potentially throwing away old data if a client does not ask for it for a while, then it may be ok to just store this in memory in a regular javascript object {}. If you do care about persisting the data between server restarts/crashes (probably best), then you can persist to something like Redis, Mongo, any of the SQL stores if your data is relational in nature, or even a regular JSON file on disk (see fs.writeFile).
Hope this helped give you a step in the right direction!
I'm trying to determine how to setup a web socket for the first time ever so a working minimal example with static variables (IP address for example instead of getservbyname) will help me understand what is flowing where.
I want to do this the right way so no frameworks or addons for both the client and the server. I want to use PHP's native web sockets as described here though without over-complicating things with in-depth classes...
http://www.php.net/manual/en/intro.sockets.php
I've already put together some basic JavaScript...
window.onload = function(e)
{
if ('WebSocket' in window)
{
var socket = new WebSocket('ws://'+path.split('http://')[1]+'mail/');
socket.onopen = function () {alert('Web Socket: connected.');}
socket.onmessage = function (event) {alert('Web Socket: '+event.data);}
}
}
It's the PHP part that I'm not really sure about. Presuming we have a blank PHP file...
If necessary how do I determine if my server's PHP install has this socket functionality already available?
Is the request essentially handled as a GET or POST request in
example?
Do I need to worry about the port numbers? e.g. if
($_SERVER['SERVER_PORT']=='8080')
How do I return a basic message on the initial connection?
How do I return a basic message say, five seconds later?
It's not that simple to create a simple example, I'm afraid.
First of all you need to check in php configuration if the server is configured for sockets with the setting enable-sockets
Then you need to implement (or find) a websocket server that at least follows the Hybi10 specification (https://datatracker.ietf.org/doc/html/draft-ietf-hybi-thewebsocketprotocol-10) of websockets. If you find the "magic number" 258EAFA5-E914-47DA-95CA-C5AB0DC85B11 in the code for the header, you can be sure it does follow at least Hybi06 ...
Finally, you need to have access to an admin console on the server in order to execute the PHP websocket server using php -q server.php
EDIT: This is the one I've been using a year ago ... it might still work as expected with current browsers supporting Websockets: http://code.google.com/p/phpwebsocket/source/browse/trunk/+phpwebsocket/?r=5
We have few node.js processes that should be able to pass messages,
What's the most efficient way doing that?
How about using node_redis pub/sub
EDIT: the processes might run on different machines
If you want to send messages from one machine to another and do not care about callbacks then Redis pub/sub is the best solution. It's really easy to implement and Redis is really fast.
First you have to install Redis on one of your machines.
Its really easy to connect to Redis:
var client = require('redis').createClient(redis_port, redis_host);
But do not forget about opening Redis port in your firewall!
Then you have to subscribe each machine to some channel:
client.on('ready', function() {
return client.subscribe('your_namespace:machine_name');
});
client.on('message', function(channel, json_message) {
var message;
message = JSON.parse(json_message);
// do whatever you vant with the message
});
You may skip your_namespace and use global namespace, but you will regret it sooner or later.
It's really easy to send messages, too:
var send_message = function(machine_name, message) {
return client.publish("your_namespace:" + machine_name, JSON.stringify(message));
};
If you want to send different kinds of messages, you can use pmessages instead of messages:
client.on('ready', function() {
return client.psubscribe('your_namespace:machine_name:*');
});
client.on('pmessage', function(pattern, channel, json_message) {
// pattern === 'your_namespace:machine_name:*'
// channel === 'your_namespace:machine_name:'+message_type
var message = JSON.parse(message);
var message_type = channel.split(':')[2];
// do whatever you want with the message and message_type
});
send_message = function(machine_name, message_type, message) {
return client.publish([
'your_namespace',
machine_name,
message_type
].join(':'), JSON.stringify(message));
};
The best practice is to name your processes (or machines) by their functionality (e.g. 'send_email'). In that case process (or machine) may be subscribed to more than one channel if it implements more than one functionality.
Actually, it's possible to build a bi-directional communication using redis. But it's more tricky since it would require to add unique callback channel name to each message in order to receive callback without losing context.
So, my conclusion is this: Use Redis if you need "send and forget" communication, investigate another solutions if you need full-fledged bi-directional communication.
Why not use ZeroMQ/0mq for IPC? Redis (a database) is over-kill for doing something as simple as IPC.
Quoting the guide:
ØMQ (ZeroMQ, 0MQ, zmq) looks like an embeddable networking library
but acts like a concurrency framework. It gives you sockets that carry
atomic messages across various transports like in-process,
inter-process, TCP, and multicast. You can connect sockets N-to-N with
patterns like fanout, pub-sub, task distribution, and request-reply.
It's fast enough to be the fabric for clustered products. Its
asynchronous I/O model gives you scalable multicore applications,
built as asynchronous message-processing tasks.
The advantage of using 0MQ (or even vanilla sockets via net library in Node core, minus all the features provided by a 0MQ socket) is that there is no master process. Its broker-less setup is best fit for the scenario you describe. If you are just pushing out messages to various nodes from one central process you can use PUB/SUB socket in 0mq (also supports IP multicast via PGM/EPGM). Apart from that, 0mq also provides for various different socket types (PUSH/PULL/XREP/XREQ/ROUTER/DEALER) with which you can create custom devices.
Start with this excellent guide:
http://zguide.zeromq.org/page:all
For 0MQ 2.x:
http://github.com/JustinTulloss/zeromq.node
For 0MQ 3.x (A fork of the above module. This supports PUBLISHER side filtering for PUBSUB):
http://github.com/shripadk/zeromq.node
More than 4 years after the question being ask there is an interprocess communication module called node-ipc. It supports unix/windows sockets for communication on the same machine as well as TCP, TLS and UDP, claiming that at least sockets, TCP and UDP are stable.
Here is a small example taken from the documentation from the github repository:
Server for Unix Sockets, Windows Sockets & TCP Sockets
var ipc=require('node-ipc');
ipc.config.id = 'world';
ipc.config.retry= 1500;
ipc.serve(
function(){
ipc.server.on(
'message',
function(data,socket){
ipc.log('got a message : '.debug, data);
ipc.server.emit(
socket,
'message',
data+' world!'
);
}
);
}
);
ipc.server.start();
Client for Unix Sockets & TCP Sockets
var ipc=require('node-ipc');
ipc.config.id = 'hello';
ipc.config.retry= 1500;
ipc.connectTo(
'world',
function(){
ipc.of.world.on(
'connect',
function(){
ipc.log('## connected to world ##'.rainbow, ipc.config.delay);
ipc.of.world.emit(
'message',
'hello'
)
}
);
ipc.of.world.on(
'disconnect',
function(){
ipc.log('disconnected from world'.notice);
}
);
ipc.of.world.on(
'message',
function(data){
ipc.log('got a message from world : '.debug, data);
}
);
}
);
Im currently evaluating this module for a replacement local ipc (but could be remote ipc in the future) as a replacement for an old solution via stdin/stdout. Maybe I will expand my answer when I'm done to give some more information how and how good this module works.
i would start with the built in functionality that node provide.
you can use process signalling like:
process.on('SIGINT', function () {
console.log('Got SIGINT. Press Control-D to exit.');
});
this signalling
Emitted when the processes receives a signal. See sigaction(2) for a
list of standard POSIX signal names such as SIGINT, SIGUSR1, etc.
Once you know about process you can spwn a child-process and hook it up to the message event to retrive and send messages. When using child_process.fork() you can write to the child using child.send(message, [sendHandle]) and messages are received by a 'message' event on the child.
Also - you can use cluster. The cluster module allows you to easily create a network of processes that all share server ports.
var cluster = require('cluster');
var http = require('http');
var numCPUs = require('os').cpus().length;
if (cluster.isMaster) {
// Fork workers.
for (var i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('exit', function(worker, code, signal) {
console.log('worker ' + worker.process.pid + ' died');
});
} else {
// Workers can share any TCP connection
// In this case its a HTTP server
http.createServer(function(req, res) {
res.writeHead(200);
res.end("hello world\n");
}).listen(8000);
}
For 3rd party services you can check:
hook.io, signals and bean.
take a look at node-messenger
https://github.com/weixiyen/messenger.js
will fit most needs easily (pub/sub ... fire and forget .. send/request) with automatic maintained connectionpool
we are working on multi-process node app, which is required to handle large number of real-time cross-process message.
We tried redis-pub-sub first, which failed to meet the requirements.
Then tried tcp socket, which was better, but still not the best.
So we switched to UDP datagram, that is much faster.
Here is the code repo, just a few of lines of code.
https://github.com/SGF-Games/node-udpcomm
I needed IPC between web server processes in another language (Perl;) a couple years ago. After investigating IPC via shared memory, and via Unix signals (e.g. SIGINT and signal handlers), and other options, I finally settled on something quite simple which works quite well and is fast. It may not fit the bill if your processes do not all have access to the same file system, however.
The concept is to use the file system as the communication channel. In my world, I have an EVENTS dir, and under it sub dirs to direct the message to the appropriate process: e.g. /EVENTS/1234/player1 and /EVENTS/1234/player2 where 1234 is a particular game with two different players. If a process wants to be aware of all events happening in the game for a particular player, it can listen to /EVENTS/1234/player1 using (in Node.js):
fs.watch
(or fsPromises.watch)
If a process wanted to listen to all events for a particular game, simply watch /EVENTS/1234 with the 'recursive: true' option set for fs.watch. Or watch /EVENTS to see all msgs -- the event produced by fs.watch will tell you the which file path was modified.
For a more concrete example, I my world I have the web browser client of player1 listening for Server-Sent Events (SSE), and there is a loop running in one particular web server process to send those events. Now, a web server process servicing player2 wants to send a message (IPC) to the server process running the SSEs for player1, but doesn't know which process that might be; it simply writes (or modifies) a file in /EVENTS/1234/player1. That directory is being watched -- via fs.watch -- in the web server process handling SSEs for player1. I find this system very flexible, and fast, and it can also be designed to leave a record of all messages sent. I use it so that one random web server process of many can communicate to one other particular web server process, but it could also be used in an N-to-1 or 1-to-N manner.
Hope this helps someone. You're basically letting the OS and the file system do the work for you. Here are a couple links on how this works in MacOS and Linux:
https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/FSEvents_ProgGuide/Introduction/Introduction.html#//apple_ref/doc/uid/TP40005289
https://man7.org/linux/man-pages/man7/inotify.7.html
Any module you're using in whatever language is hooking into an API like one of these. It's been 30+ years since I've fiddled much with Windows, so I don't know how file system events work there, but I bet there's an equivalent.
EDIT (more info on different platforms from https://nodejs.org/dist/latest-v19.x/docs/api/fs.html#fswatchfilename-options-listener):
Caveats#
The fs.watch API is not 100% consistent across platforms, and is unavailable in some situations.
On Windows, no events will be emitted if the watched directory is moved or renamed. An EPERM error is reported when the watched directory is deleted.
Availability#
This feature depends on the underlying operating system providing a way to be notified of file system changes.
On Linux systems, this uses inotify(7).
On BSD systems, this uses kqueue(2).
On macOS, this uses kqueue(2) for files and FSEvents for directories.
On SunOS systems (including Solaris and SmartOS), this uses event ports.
On Windows systems, this feature depends on ReadDirectoryChangesW.
On AIX systems, this feature depends on AHAFS, which must be enabled.
On IBM i systems, this feature is not supported.
If the underlying functionality is not available for some reason, then fs.watch() will not be able to function and may throw an exception. For example, watching files or directories can be unreliable, and in some cases impossible, on network file systems (NFS, SMB, etc) or host file systems when using virtualization software such as Vagrant or Docker.
It is still possible to use fs.watchFile(), which uses stat polling, but this method is slower and less reliable.
EDIT2: https://www.npmjs.com/package/node-watch is a wrapper that may help on some platforms
Not everybody knows that pm2 has an API thanks to which you can communicate to its processes.
// pm2-call.js:
import pm2 from "pm2";
pm2.connect(() => {
pm2.sendDataToProcessId(
{
type: "process:msg",
data: {
some: "data",
hello: true,
},
id: 0,
topic: "some topic",
},
(err, res) => {}
);
});
pm2.launchBus((err, bus) => {
bus.on("process:msg", (packet) => {
packet.data.success.should.eql(true);
packet.process.pm_id.should.eql(proc1.pm2_env.pm_id);
done();
});
});
// pm2-app.js:
process.on("message", (packet) => {
process.send({
type: "process:msg",
data: {
success: true,
},
});
});