We're planning on adding SignalR to several differnet web applications. The applications are targeted different aspects of an order. When something happens to an order, all users working with the order across all web applications should be notitfied.
Changes to an order are availible asa message on a servicebus.
We could implement the following logic in all web applications:
Subscribe to a topic (one subscription per webapp)
OnMessage -> Send orderId to hub
Hub would notify clients working on the orderId
Question is: Could we implement all this common functionality in a separate application, and all web apps would reference the same signalr scripts?
All applications live on the same domain, and it would give us a lot of benefit not having to implement signalr in every app.
Good idea, or am I missing something important here?
Edit: Put in other words: I have WebAppA, WebAppB and WebAppC all without SignalR. I'm asking if its possible to create a WebappD that talks to clients in WebApp A,B,C
Second Solution is very good. it will move signalr load (espcially memory) from your main web apps to WebAppD(signalr web app). And all your main web apps will not be dependent to signalr.
Drawbacks: You don't have any authentication on WebAppD. Because clients are authenticated on the other WebApps. You should let the WebAppD knows about orderId. That's why, you should send message to server (WebAppD) from clients(Javascript).
Because of enable cross domain settings, anyone can send message to server. Even they don't need to be connected WebAppA,WebAppB or WebAppC. Even if you solve this problem (virtual path etc), Someone is connected but not authenticated on WebAppA,WebAppB,WebAppC can sends message. Because WebAppD just get the message and it doesn't know this client is authenticated or not so it will serve this message to all others. In Short: Someone can send fake messages to other clients.
So you should share your authentication like this (or some other logic) between your web app and signalr webapp.
Other than this I couldn't see any drawback.
Related
I am new to web development but I have a project done in VB6, it is a real time send and receive sms application. It uses a GSM modem connected to the server. My company asked me to make a web based version of my application, using ASP.NET MVC.
So I studied MVC about a month ago, created basic CRUD apps, read about SignalR but I don't want to start up a project that I am not confident if its feasible or not. So my question is, is this project possible with the said technology? (MVC, SignalR, and a GSM Modem)
If it is, can you point me somewhere I could start reading for maybe you know a similar project that can guide me through.
And if it is not, can you suggest me the appropriate tech to use for this project to be feasible? (I prefer ASP.NET MVC)
A little detail about the functionality of the project:
Has User Authentication - this user will have a simple "SMS box" type of thing which will update like a chatbox if an SMS is received in the GSM modem and this user can reply and use the GSM to send the SMS back to the sender.
IF anyone could help me, guide me, point me to some reading materials to make this project it would be greatly appreciated. Please post if you need clarifications and further explanation. Thanks!
User,
There are many ways to achieve this, so I will explain a method that worked for me a while back doing exactly this.
Based on the information provided, I will assume that you have a windows desktop app, that can already talk to the modem and perform various functions.
Trying to perform that same tasks in a web application can be a hard path to go down, what I opted for was rather simple in my opinion. You really have two separate problems, one is getting the received messages to the web application and the other getting the web application to send messages to the modem.
For handling received messages, I created a simple web api in the web application and defined a post method that is able to receive a sms object. You will need to provide the url for this call to your code that resides in your modem project, which I would convert to a windows service, if it is not already. Then when your code fires when the modem has received a sms, you simply create a object, serialize it to xml or json and then call the post method in your web api. This will give you the chance to use SignalR to notify clients or whatever else you might need to do. This is honestly is the simple part and you have the "real-time" handling ability now for receive.
For sending, there again where many options, I opted for database polling from the code inside the windows service, so when a user wants to reply or send a message, the message gets stored in a table in a database, from where the service code will pick it up and send it, once sent it will mark a field in the table as sent and possibly add a date and time as to when this happened. Again your service code could call another method on your web api, that will notify your app, that a message was sent and again you could notify the end user.
As for database polling, there are various methods, you could simply run some code every minute or some configurable value to see if there are any unsent messages.
You could use SqlDependency and handle the events in real time, you would register an event against the table where messages to be sent will be inserted into and when this happens, your service code will receive a real time event which can be handled.
You could also in the windows service, create a service, even a self hosted web api again, which can be called from your web application when it wants to send an email.
I did various implementations based on client requirements, but for me hosting either a wcf service or web api in the windows service project, proved to be the best in my opinion. You then simply have a configuration section in your web application, and provide the service address, or uri for the post method.
I hope that I have given you enough ideas to get a starting point for your project.
I have a smart grid system where multiple hardware devices are sending raw sensor data to an Azure Queue. Each device sends a single data packet once every minute. Multiple Worker Roles process the data packets on the queue and push the data to Table Storage. I have a Web Role which holds the application for users to view their device data and a host of other alerts and messages relating to their smart energy system. At the moment the web application just uses ajax polling at one minute intervals to get the latest data updates and any other messages and alerts. Instead of using ajax 'pulling', I'd like to use SignalR instead and 'push' the updates from the cloud when they become available. I'm not sure on what the overall architecture might look like.
So far I have added a SignalR Hub to my Web Role, just to see if I could do that. And it works fine. However, how do I trigger updates from this Hub when there are changes in Table Storage? Should I host the Hub with the Worker Roles that process the raw data, and then make a cross-domain SignalR connection from the web app (client)? Can I even associate an endpoint with a Worker Role? If I have many Worker Roles wouldn't I only be able to connect to one of them, and therefore miss data updates from other Worker Roles?
Perhaps I should create a separate Web Role to host the SignalR hub, but then how do I communicate the changes from the Worker Roles that process the raw data to the hub? Maybe I need to include another Azure Queue that takes messages from the Worker Roles regarding data updates, alerts, and any other messaging, and that queue is processed by the SignalR server. However, would this approach be scalable? If I have multiple instances of the SignalR server processing the message queue(s), would they share the same end point and be aware of all the client connections across the instances? Or maybe the Worker Roles themselves connect as clients to the SignalR server and the messages forwarded from there to the clients.
Is SignalR even the right approach to take if data is being generated at a predictable rate of once every minute for each device. Maybe for updates of this regular data ajax 'pulling' is the best approach, and I should just be using SignalR for the infrequent alerts and messages, although, again, how do I communicate these events from the Worker Roles to the SignalR server?
What overall architecture would suit my needs here?
EDIT 06-09-2014 Half the problem solved
I came across http://www.asp.net/signalr/overview/signalr-20/performance-and-scaling/scaleout-with-windows-azure-service-bus which seems to be exactly what I am after. This deals with the problem of multiple Hub server (Web Role) instances. Now I just need a SignalR client library that can run on the Worker Roles so that they can notify the Hub that new data is available, and the Hub class can then be enhanced to route the new data to the appropriate connected web clients.
EDIT 06-10-2014 A workable solution found
I have added an answer to my question of "What architecture". I thought a quick summary of my setup might be useful. I have many remote devices associated with different users posting real-time data to Azure Queues. The data posted to these queues are parsed and saved to Table Storage, by a number of Worker Roles. Web Roles provide the MVC5 web application for the users (clients) to log on and review their data. I wanted a mechanism by which when new data was posted, any connected clients would receive a real-time notification (and data tables and charts in the client apps could be updated accordingly). SignalR with Service Bus scaleout proved to be the answer.
The first part of the solution I needed was to deploy a SignalR hub that the clients could connect to, to receive any notifications sent. I couldn't use the basic SignalR solution as the MVC5 web app is hosted on a Web Role that will likely have more than one instance - the problem was how to keep all these instances synced so that whatever instance a client was connected to they'd still receive the notifications. SignalR scaleout with Azure Service Bus proved to be the answer to that part of the problem. Details of how to set this up can be found at: http://www.asp.net/signalr/overview/signalr-20/performance-and-scaling/scaleout-with-windows-azure-service-bus - it was VERY easy to setup.
The second part of the problem was how to generate the notifications originating from the Worker Roles (my queue data processors). First I needed to be able to host OWIN in my worker roles - the instructions provided at http://www.asp.net/aspnet/overview/owin-and-katana/host-owin-in-an-azure-worker-role were more than sufficient. Once this was done I created an empty Hub instance with the same name as the one deployed on my Web Roles (it was empty because I didn't expect to have an clients connected to it directly), and changed the Startup class to:
public class Startup
{
public void Configuration(IAppBuilder app)
{
String connectionString = "[Service Bus Connection String]";
GlobalHost.DependencyResolver.UseServiceBus(connectionString, "[App Name]");
app.MapSignalR();
}
}
With this in place if I want to send a notification out to the clients, from the Worker Roles, I do something like:
var context = GlobalHost.ConnectionManager.GetHubContext<MyHub>();
context.Clients.All.clientMethod("[Message]");
What really happens is that a copy of the message gets pushed to the backplane (Service Bus) and is picked up by the Web Roles and pushed out to the connected clients. In reality I will check who is online (in the Web Role Hub instance I override the OnConnected method to save the user's connection id in their profile which is stored in Table Storage), and only create notifications that are associated with those users to reduce SignalR traffic.
I'm currently hosting 2 webstites (clientportal and admin), in windows azure websites.
I'm going to introduce SignalR right now, to get rid of javascript polling. What I need, is when an admin send a broadcast message on the admin site, all the active client should be receive it. Now, the clien polls the webserver all the time, when an ajax poll receives, the webserver check for new messages in the database.
What would be the best way, to notify the client webserver from the admin webserver? WebApi is ok for this? Or are there any simple way?
From the point of view of Azure Websites and SignalR, it is transparent who is the Client and who is the Admin. This is an implementation detail, and thus, there are many ways to do it.
SignalR is split in two parts: The javascript library, and the .NET library that you use to create your "Hub". One way to accomplish what you are trying to do is to implement the Hub functionality in your Admin back-end using the .NET side of SignalR and ASP.NET Web API; and use the javascript side of SignalR to subscribe and listen for notifications on the Client side.
Another way to do it is to create a third component, just for the SignalR Hub, independent of both the Client and the Admin websites. In this scenario both the Admin and the Client would subscribe to the Hub, but only the Admin would push, and the Client would listen.
You can find many working examples on the internet. This is one of them: http://msdn.microsoft.com/en-us/magazine/hh965663.aspx
I hope this answers your questions.
I'm developing an application that has various types of Notifications. Examples of notifications:
Message Created
Listing Submitted
Listing Approved
I'd like to tie all of these up to SignalR so that any connected clients get updates in real-time.
As far as architecture goes - right now the application is entirely within a single solution hosted on an Azure Website. The triggers for each of these notification types live within this application.
When a trigger is hit, I'd like to tell signalR, "Hey, send this message to the following clients" along with a list of userIds. I'm assuming that it's possible to identify connected clients based on userId... and I'm assuming that the process of send message to clients should be executed outside of the web application, so as to not slow down the MVC app or risk losing data in a broken async call. First question - are these assumptions correct?
Assuming so, this means that I'll need something like a dedicated web/worker role to be sending messages to clients. I could pass messages from my web application directly to this process, but what happens if the process dies? The resiliency concerns lead me to believe that the proper way to pass messages would be via a queue of some sort. Second question - is this a valid train of thought?
Assuming so, this means that I can either use a good ol' Azure SQL database as a queue, but it seems like there are some specialized (and maybe cheaper) services to handle message queueing, such as this:
http://www.windowsazure.com/en-us/develop/net/how-to-guides/queue-service/
Third question: Should this be used as a queueing mechanism for signalR? I'm interested in using Redis for caching in the future... would Redis be better or worse than the queue service?
Final Question:
I've attempted to illustrate my proposed architecture here:
What I'm most unclear on here is how the MVC app will know when to queue, or how the SignalR processes will know when to broadcast. Should the MVC app queue blindly, without caring about connected clients? This seems to introduce a lot of wasted space on the queue, and wasted cycles in the worker roles, since a very small percentage of clients will ever be connected.
The only other approach I can think of is to somehow give the MVC app visibility into the SignalR processes to see if the client is connected... and if they are, then Enqueue. This makes me uncomfortable though because it means I have to hit that red line on the diagram for every trigger that gets hit, which - even if done async - gets me worrying about performance and reliability.
What is the recommended architecture for scalable, performant SignalR message broadcasting? Performance is top priority, followed closely by cost.
Bonus question:
What if some messages are of higher priority than others? Should two queues be used, one of which always gets checked before the other?
If you want to target some users, you'll have to come up with a mechanism, off the top of my head I can give an example, if any user hits a page, you can create a group for that page and push to all users in that group/in that page.
It's not clear to me why you need the queues. Usually users subscribe to some events when hitting a page or by some action like join a chat room, and the server pushes data using those events/functions when appropriate.
For scalability, you can run signalr in different servers, in which case you should use sql server, or service bus or redis as a backplane.
Firstly you need to create a SignalR server to which all the users can connect to. This SignalR server can be created either in the web role or worker role. If you have a huge user base then its better to create the SignalR server on a separate role.
Then wherever the trigger is hit and you want to send messages to users, you have to create a SignalR client (.NET or javascript) and then connect to SignalR server. Then you can send the message to SignalR server which in turn will broadcast to all the other users connected. After that you can disconnect the connection with SignalR server. This way you dont have to use queues to communicate with the SignalR role.
And also to send messages to specific users you can store the socket id's along with their user id's in a table (azure table storage should do) when they connect to SignalR server. Then using socket id you can send messages to specific user.
In a DELPHI 2007 application that I am developing some prospect clients just found interesting to be able to share data and information with each other.
They all have the same application.
All have independent Databases
But all have the same installed application and there are some data types that they might want to share (replicate) between their databases.
How can I enable them to share data with other users of the same application program, but not to everybody on the whole internet.
I would like this to be as automatic as possible, as I already have considered approaches that involve manually sending emails.
I know Datasnap is an option, is there any other.
UPDATE:
The idea is to enable companies that have the same application to be able to share data.
They should be able to select what partner and what to send.
I have been investigating datasnap, but would like to know if there is another way to do this
Another standard way to connect distributed applications and share data and information is through some Message-oriented middleware (MOM). There are many open source middleware products (message brokers) available, which can be used over Delphi client libraries, even in multithreaded Delphi server applications. (Disclaimer: I am the author of message broker client libraries for Delphi and Free Pascal)
There are many essential differences between web services and message brokers, like peer-to-peer and publish/subscribe communication models. They also play a key role in enterprise application integration patterns.
One standard way to connect applications to other applications is to make a web-service, and make a client that consumes that web-service, called a web-client. Technologies like SOAP and REST refer to such web service and web clients.
Your question is vague, perhaps due to english not being your language, but you should probably edit it and be more specific.
If all your applications are going to talk directly to each other that is called "peer to peer networking" and there are huge problems with enabling that kind of communication directly over the internet. It is much easier if you build a server that all these applications will connect to.
As a sample, consider the IRC Chat service, and consider writing a Web Service that will be the Chat Server, and consider all your clients to be "Chat clients". Sharing data could be the same idea as creating "rooms" or "channels" on a chat server.
I get the idea that you want something like a Peer to Peer Data Replication Service. I think that the closest you're going to get to that is something like "RSS Feeds" (used by blog syndication services). You subscribe to them via a simple web service, and pull down the new content on some periodic basis. Since that data has to be published to a central server, that means, that a peer to peer approach is out of the question. If you don't have your own web server running on a web hosting service, or on a "cloud", and you need a truly peer to peer solution, I am not aware of any way to do that, at least not without an incredible custom engineering effort.