I have a Spring Boot stomp server running. When a client is connected the method simpUserRegistry.getUserCount() returns the count of connected users, but when the client is disconnected still the user count is not changed (I believe it should decrease).
I don't know why it is happening. It's like the users are always connected.
Related
We want to use spring websockets + STOMP + amazon MQ as a full featured message broker. We were trying to do benchmarking, to find out how many client websocket connections single tomcat node can handle. But it appears that we hit amazonMQ connection limit first. As per the aws documentation, amazonMQ has a limit of 1000 connections per node (as far as I understand we can ask support to increase the limit, but I doubt that it can be increased big time). So my questions is:
1) Am I correct in assuming that for every websocket connection from client to spring/tomcat server, a corresponding connection being opened from server to broker? Is this correct behavior or we're doning something wrong here/missing something?
2) What can be done here? I mean I don't think this is a good idea to create broker node per evry 1000 users..
According to https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/messaging/simp/stomp/StompBrokerRelayMessageHandler.html your are doing everything right, and it is documented behavior.
Quote from javadoc:
For each new CONNECT message, an independent TCP connection to the broker is opened and used exclusively for all messages from the client that originated the CONNECT message. Messages from the same client are identified through the session id message header. Reversely, when the STOMP broker sends messages back on the TCP connection, those messages are enriched with the session id of the client and sent back downstream through the MessageChannel provided to the constructor.
As for a fix, you can write your own message broker relay, with tcp connection pooling.
I have an application in which clients use websockets to connect to a server which is running Spring Boot Tomcat.
My question is if there is a way for the server to detect a client disconnect due to a network loss.
Thanks.
if you are using stomp , check SessionDisconnectEvent.
For raw Websocket connections, you can use :
WebSocketHandler-->afterConnectionClosed
I have searched before for this and the solution I was able to find was to implement a ping-pong mechanism between the server and the clients.
For example, each few seconds send a dummy message to the client on a specific topic and receive back another dummy reply, if you didn't get a reply for a configured period you can consider the client disconnected.
As mentioned here,
STOMP and Spring also allow us to set up topics, where every
subscriber will receive the same message. This is going to be very
useful for tracking active users. In the UI, each user subscribes to a
topic that reports back which users are active, and in our example
that topic will produce a message every 2 seconds. The client will
reply to every message containing a list of users with its own
heartbeat, which then updates the message being sent to other clients.
If a client hasn't checked in for more than 5 seconds (i.e. missed two
heartbeats), we consider them offline. This gives us near real time
resolution of users being available to chat. Users will appear in a
box on the left hand side of the screen, clicking on a name will pull
up a chat window for them, and names with an envelope next to them
have new messages.
We are using tomcat websocket implementation in our web application. Messages are pushed from server to client through websockets. Web socket messages are not pushed when intermittant connection drop or network is switch over but still web application is connected.
Let say for example i am connected to LAN and logged in app, now i connecting through wifi after wifi successfully connected i am disconnecting LAN with in fraction of second network is switched from LAN to wifi But after this messages are not pushed from server to client through websockets.
After network switch if i check the state of the websocket(readyState) which says 1 which means websocket connection is open but actually its not.
Can anyone faced this issue earlier and provide your suggestions.
Thanks
You must create a connection drop detection mechanism. The WebSocket protocol has ping/pong frames, but I don't know if Tomcat has that functionality. In some Webscoket frameworks you can define a timeout interval, and the server will ping the client regularly, if the client miss some pongs is disconnected.
If that functionality is not provided by Tomcat, you can still create your own. Just define a special type of message and repeat it to the server from the client. If you do not get any of those messages for a while, disconnect.
Case:
A WebSocket connection have been established between the client and server endpoint.
Now I have the network connection go down (for example the ADSL dies), after 10 min I recover the network, I find that the client and server are still able to communicate with each
other. Why?
Note:
The client was developed with Java-WebSocket framework, and the client did with ws4py.
1 - If they did not try to exchange any data and only the connection (not the endpoints) between them is down, this is normal behaviour.
2 - If the websocket connection ended, Browser may have re-established it without you knowing about it. I just checked that this is not normal behaviour. But maybe there is some parameter somewhere :-)
I am new to Websockets. While reading about websockets, I am not been able to find answers to some of my doubts. I would like if someone clarifies it.
Does websocket only broadcasts the data to all clients connected instead of sending to a particular client? Whatever example (mainly chat apps) I tried they sends data to all the clients. Is it possible to alter this?
How it works on clients located on NAT (behind router).
Since client server connection will always remain open, how will it affect server performance for large number of connections?
Since I want all my clients to get real time updates, it is required to connect all my clients to server, so how should I handele the client connection limit?
NOTE:- My client is not a Web browser but a desktop application.
No, websocket is not only for broadcasting. You send messages to specific clients, when you broadcast you just send the same message to all connected clients, but you can send different messages to different clients, for example a game session.
The clients connect to the server and initialise the connections, so NAT is not a problem.
It's good to use a scalable server, e.g. an event driven server (e.g. Node.js) that doesn't use a seperate thread for each connection, or an erlang server with lightweight processes (a good choice for a game server).
This should not be a problem if you use a good server OS (e.g. Linux), but may be a limitation if your server uses a desktop version of Windows (e.g. may be limited to 200 connections).