I'm building a system where client IoT devices will be making persistent websocket connections to a single instance of a microservice. We'll call it the "hardware gateway". End devices will be connecting to one of these service instances and may migrate between services at anytime (perhaps due to a reboot or network interruption).
Other services will be pushing notifications to these hardware clients via some hardware gateway instance. I need a way to route these requests to the specific instance that is maintaining a connection to a specific IoT device. At the moment, my solution is to maintain an external KV store where I can map an IoT device's UUID to a service instance, but that puts an extra dependency on all other services to know about this KV store. Not to mention the additional latency introduced by this query.
Maybe there's some reverse proxy that allows me to dynamically update its matching criteria? I've also looked into using a message broker like RabbitMQ, but it doesn't seem to support this use case.
There's a reasonable solution in JVM land for this: Akka.
The instances form an Akka cluster. When a device makes a websocket connection, an actor is spawned to handle the interactions over the websocket. The actor registers that it is the actor interacting with the device with a cluster sharded actor keyed by the device's ID (and likely periodically reregisters with the sharded actor). As instances are deployed, etc. the cluster rebalances. An important feature of this is that the service is stateful, but the instances deploy in a way that looks to the outside world like it's stateless: requests can go to any node.
For pushing notifications to the devices, the HTTP endpoint or message-bus consumer in the service looks up the cluster sharded actor which forwards the notification to the websocket actor (you'll want to think about whether you want at-least-once or at-most-once delivery, which will govern whether there's some portion of the cluster sharded actor which should be persistent).
Related
I have exposed a websocket enabled service endpoint through Azure Application Gateway and the service is hosted on azure service fabric. Client initiates a websocket connection with my endpoint and is able to exchange data. During certain message flows, my Web Socket enabled service calls other services hosted on the service fabric using azure service bus. These are handled in a completely async manner. Once the other services finish processing, they post a message to the service bus which my WebSocket service reads back.
The problem I am having is to route the messages back to the right service fabric node so that it can be pushed back to the client at the other end of the WebSocket connection
In the picture below, you can imagine each node containing multiple services including the web socket enabled service. Once the Websocket service posts a message to the service bus, the downstream services start processing and finally they post a message back to the service bus which the websocket service reads back. Here a random node will pick up the message and it might not have the relevent websocket connection to push the processed data back
Sample Design
I have looked at redis pubsub model and it looks like I have to maintain last message processed on the nodes. It also means, every node on the cluster will need to read the message and discard it if they don't have the websocket connection with the client. I am looking for any suggested design models for this kind of problem
I ran into a similar scenario and didn't like the idea of using a new external service (Redis/SQL Server) as a backplane that would simply duplicate each message/event across all nodes.
The solution I settled on was to lean on a property of actor proxies, using actor events to call-back to a specific instance of a stateless service. Creating an actor service to act as a pub/sub backplane.
The solution is summarised in this blog post and this GitHub repo. It's worth pointing out that the documentation states actor events are best effort. This hasn't really been an issue when the application is running as normal, I presume that during a deployment or failover, some events may get lost, however this could be mitigated with additional work.
It's also worth noting that your load balancing rules should maintain sticky connections between clients and back-end instances. You could create separate rules for websockets if you only wanted this to apply to them and not your regular HTTP traffic.
I would like to figure out the best way to route messages from Kafka to web socket clients connected to a load balanced application server cluster. I understand that spring-kafka facilitates consuming and publishing messages to a kafka topic, but how does this work in a load balanced application server scenario when connecting to a distributed kafka topic. Here are the requirements that I would like to satisfy, with the overall goal of facilitating peer to peer messaging in an application with a very, very large volume of users:
Web clients can connect to a tomcat application server via web sockets connection via a load balancer.
Web client can send a message/notification to another client thats connected to different tomcat application server.
Messages are saved in the database and published to a kafka topic/partition that can be consumed by the appropriate web clients/users.
Kafka can be scaled to many brokers with many consumers.
I can see how this can be implemented quite easily in a single application server scenario where the consumer consumes all messages from a kafka topic and re-distributes via spring messaging/websockets. But I can't figure out how this would work in a load balanced application server scenario where there are consumers on each application server forming an overall consumer group for the kafka topic. Assuming that each of the application servers are are consuming sub-sets/partitions of the kafka topic, how do they know which server their intended recipients are connected to? And even if they knew which server their recipients were connected to, how would they route the message to them via websockets?
I considered that the application server load balancing could work by logging users with a particular routing key (users starts with 'A' etc) on to a specific application server, then only consuming messages for users starts with 'A' on that application server. But this seems like it would be difficult to maintain and would make autoscaling very difficult. This seems like it should be an common scenario to implement but I can't find any tools or approaches that fit this scenario.
Sounds like every single consumer should live in its own consumer group. This way all the available consumers are going to consume all the messages sent to the topic. Therefore all the connected websocket clients are going to be notified with those messages.
If you need more complex logic with those messages at
after consuming, e.g. filtering, routing, transforming, aggregating etc., you should consider to involve Spring Integration in you project: https://spring.io/projects/spring-integration
Broadcast to all the consumer may work, but the most efficient solution should route message to the node holds the websocket connection for the target user precisely. As i know, route in a distributed system can be done as follows:
Put the route information in a middleware，such as Redis; Or implement a service by yourself to keep track of all the ssesions. That is, solved in a centralized way.
Let the websocket server find route by themselves. In this circumstance, consensus algorithm like gossip should be taken into consideration.
As illustrated above, I need to build a Vert.x Java app that will be an HTTP server/virtual host (TLS Http traffic, Web socket traffic) that will redirect/channel specific domain traffic to other Vert.x Java apps running on the same server, each in it's own JVM.
I have been reading for days but I remain uncertain as to how to approach all aspects of the task.
What I DO know or have experience with:
Creating an HTTP server, etc
Using a Vert.x VirtualHost handler to "handle" incoming traffic for a
specific domain
What I DO NOT know:
How do I "re-direct" a domain's traffic to another Vert.x app (this
other Vert.x app would also be running on the same server, in its own
JVM).
- Naturally this "other" Vert.x app would need to respond to HTTP
requests, etc. What Vert.x mechanisms do I employ to accomplish this
aspect of the task?
Are any of the following concepts part of the solution? I'm unfamiliar with these concepts and how they may or may not form part of the solution.:
Running each Vert.x app using -cluster option?
Vert.x Streams?
Vert.x Pumps?
There are multiple ways to let your microservices communicate with each other, the fact that all your apps are running on the same server doesn't change much, but it makes number 2.) easy to configure
1.) Rest based client - server communication
Both host and apps have a webserver
When you handle the incoming requests on the host, you simply call another app with a HttpClient
Typically all services find each others address via service discovery.
Eg: each service registers his address in a central registry then other services use this central registry to find the addresses.
Note: this maybe an overkill for you and you can just configure the addresses of the other services.
2.) You start the vertx microservices in clustered mode
the eventbus is then shared among the services
For all incoming requests you send a broadcast on the eventbus
the responsible app replies to the message
For further reading you can checkout https://vertx.io/docs/vertx-hazelcast/java/#configcluster. You start your projects with -cluster option and define the clustering in an xml configuration. I think by default it finds the services via local broadcast.
3.) You use a message broker like RabbitMq etc.
All your apps connect to a central message broker
When a new request comes in to the host, it sends a message to the message broker
The responible app then listens to the relevant messages and replies
The host receives the reply from the message broker
There are already many existing vertx clients for certain message brokers like kafka, camel, zeromq:
https://github.com/vert-x3/vertx-awesome#integration
I have two different service fabric applications. Both are stateless web api models. I do have a situation that from service 1 inside application 1, I need to invoke service 2 which is part of application 2. I am deploying both applications in the same cluster. Can someone advise the best practice here. What could be best way to communicate. Please provide some sample as well.
Fabric Transport (aka Service Remoting) is the sdk built-in communication model. Compared to communication over HTTP or WCF it does a little more, especially on the client side of the communication.
When it comes to communicating with Service Fabric services (or really, any distributed systems service) your communication should take into account that the connection could be fail to established on an initial try, or be interrupted mid communication and that you really shouldn't build your solution to expect it to always work flawlessly. The reason for this is in the nature of how Service Fabric at any time can decide to move primaries from a node to another node, the nodes themselves can go down and the services can crash. Nothing strange about he great thing with Service Fabric is that it does a lot of the heavy lifting for you when it comes to maintaining your services and nodes over time.
So, in terms of communication this means that a client needs to be able to do three things (for it to truly work in a distributed environment);
resolve the address to the service (figure out which node it is on, which port it is listening on, which partition id and replica to target and so on)
connect to the service, package and send requests and then recieve and unpack responses
retry the resolve and connect if the communication fails
Fabric Transport does all this when you are using the Service Remoting clients (like ServiceProxy) and service side listeners.
Thats the good part with Fabric Transport, you get all that out of the box and most of the time you don't have to change the default setup either. The bad part is that it only works for communication inside the cluster, i.e. you cannot communicate from the outside to a service running in the cluster using Fabric Transport. For that you need HTTP or WCF.
HTTP(s) and WCF (over HTTP(s)) communication allow you to build your own clients and handle the communication yourself. There are a number of samples on how you can do the resolve, connect and retry for HTTP clients, this one for instance
According to Microsoft there are three built-in communication options. It's up to you to decide which one works best for you. I'm personally using service remoting which is easy to quickly set up. It also allows you to exception handling in your client service.
I'm currently using Socket.IO with redis store.
And I'm using Room feature with it.
So I'm totally okay with Room join (subscribe)
and Leave (unsubscribe) with Socket.IO.
I just see this page
http://www.rabbitmq.com/blog/2010/11/12/rabbitmq-nodejs-rabbitjs/
And I have found that some people are using Socket.IO with rabbitMQ.
Why using Socket.IO alone is not good enough?
Is there any good reason to use Socket.IO with rabbitMQ?
SocketIO is a browser --> server transport mechanism whereas RabbitMQ is a server --> server message bus.
The two can be implemented together to create a very responsive system in scenarios where a user journey consists of a message starting life on a browser and ending up in, say, some persistence layer (such as a database).
A message would be transported to the web server via socketIO and then, instead of the web server being responsible for persisting the message, it would drop it on a Rabbit queue and leave some other process responsible for persisting it. This way, the web server is free to return to its web serving responsibilities and, crucially, lessening its load.
Take a look at SockJS http://sockjs.org .
It's made by the RabbitMQ team
It's simpler than Socket.io
There's an erlang server for SockJS
Apart from that, there is an experimental project within RabbitMQ team that intends to provide a SockJS plugin for RabbitMQ.
I just used rabbitMQ with socket.io for a totally different reason than in the accepted answer. It wasn't that relevant in 2012, that's why I'm updating here.
I'm using a docker swarm deployment of a chat application with scalability and high availability. I have three replicas of the chat application (which uses socket.io) running in the cluster. The swarm cluster automatically load-balances the incoming requests and at any given time a client might get connected to any of the three replicas of the application.
With this scenario, it gets really necessary to sync the WebSocket responses in the replicas of the application because two clients connected to two different instances of the application wouldn't get each other's messages because they've been connected to different WebSockets.
This is where rabbitMQ intervenes. It syncs all the instances of the application and whenever a message is pushed from a WebSocket on a replica, it gets pushed by all replicas.
Complete details of the project have been given here. This is a potential use case of socket.io and rabbitMQ use in conjunction. This goes for any application using socket.io in a distributed environment with high availability and scalability.