I'm designing a Client/Server App in C# where all the Model Object and calculation has to be done on the server. The server doesn't need a specific UI.
Meanwhile I'd like my clients to be able to execute different functions or services from the server and receive the result of the computation from it as well as binding or subscribing to some values and each time the server update it, it sends the update to all clients who subscribed to this value.
Nothing spectacular in this I think.
I dont have any background in Network or Server-Client apps.
My question is the following:
I'd like to bind directly properties of my ViewModel which is Server side to the View which is Client Side.
Is there a way for me to do this like if the view was in a normal local MVVM framework?
I'd like to avoid having to create a specific language between the clients and the server and having then to handle the queue and priorities of clients messages.
If not, would you have some readings to recommend ?
Many Thanks.
You don't want your views to rely on a network connection to stay responsive, even if you solve the technical challenges of what you are proposing. Networking should be done in a way that can fail gracefully.
This is bad and you should not do it. That's my opinion.
Additionally, you really shouldn't be designing your own protocol for communication. You could use something like WCF or another framework that allows you to just call a remote function.
Related
I am using C# ASP.NET MVC 4 Razor
I have a Grid in ASP.NET MVC Razor View that displays the user records. Is there any way to show the new users in Grid without sending the async request to server after each 1 min ?
I searched on Google a lot. Now, finally I am posting the query here to get any clue for this solution to avoid Traffic on Server. As this page will be visible to at least 20,000 users
#Christos approach is the right one!, Just to add more info about it for an ASP.NET solution I would it use SignalR, that lets you implement a simple server/client communication and it's cross browser (it has several polyfills that if it cannot use web sockets it will use server-sent event, and so on), and the best part is that you don't need to worry about that implementation.
Once your clients are connected to the signalR server you can notify them everytime you need to add a new item to the grid.
http://www.asp.net/signalr/overview/getting-started/tutorial-server-broadcast-with-signalr
I hope it helps!
You could make use of the the publish/subscriber pattern. This can be done using for instance a redis server.
In software architecture, publish–subscribe is a messaging pattern
where senders of messages, called publishers, do not program the
messages to be sent directly to specific receivers, called
subscribers. Instead, published messages are characterized into
classes, without knowledge of what, if any, subscribers there may be.
Similarly, subscribers express interest in one or more classes, and
only receive messages that are of interest, without knowledge of what,
if any, publishers there are.
Please have a look here.
Doing so, the first time a client requests data from the server will subscribe to the server for taking any updates. Once any update arrives, the server will push the update to the clients that have subscribed, without requiring from the client to make any other request to the server.
As for implementation details, please have a look here.
We have a number of different old school client-server C# WinForm client-side apps that are essentially front-ends for the database. Then there is a C# server-side windows service that waits on the client apps to submit orders and then it processes them.
The way the server-side service finds out whether there is work to do is that it polls the database. Over the years the logic of polling for waiting orders has gotten a lot more complicated due to the myriad of business rules. So because of this, the polling stored proc itself uses quite a bit of SQL Server resources even if there is nothing to do. Add to this the requirement that the orders be processed the moment they are submitted and you got yourself a performance problem, as the database is being polled constantly.
The setup actually works fine right now, but the load is about to go through the roof and, it is obvious, that it won't hold up.
What are some effective ways to communicate between a bunch of different client-side apps and a server-side windows service, that will be more future-proof than the current method?
The database server is SQL Server 2005. I can probably get the powers that be to pony up for latest SQL Server if it really comes to that, but I'd rather not fight that battle.
There are numerous options ways you can notify the clients.
You can use a ready-made solution like NServiceBus, to publish information from the server to the clients or other servers. NServiceBus uses MSMQ to publish one message to multiple subscribers in a very easy and durable way.
You can use MSMQ or another queuing product to publish messages from the server that will be delivered to the clients.
You can host a WCF service on the Windows service and connect to it from each client using a Duplex channel. Each time there is a change the service will notify the appropriate clients or even all of them. This is more complex to code but also much more flexible. You could probably send enough information back to the clients that they wouldn't need to poll the database at all.
You can have the service broadcast a UDP packet to all clients to notify them there are changes they need to pull. You can probably add enough information in the packet to allow the clients to decide whether they need to pull data from the server or not. This is a very lightweight for the server and the network, but it assumes that all clients are in the same LAN.
Perhaps you can leverage SqlDependency to receive notifications only when the data actually changes.
You can use any messaging middleware like MSMQ, JMS or TIBCO to communicate between your client and the service.
By far the easiest, and most likely the cheapest, answer is to simply buy a bigger server.
Barring that, you are in for a development effort that has a high probability of early failure. By failure I don't mean that you end up scraping whatever it is you end up building. Rather, I mean you launch the changes and orders will be screwed up while you are debugging your myriad of business rules.
Quite frankly, I wouldn't consider approaching a communications change under pressure; presuming your statement about load going "through the roof" in the near term.
If your risk exposure is such that it has to be 100% functional day one (which is normal when you are expecting a large increase in orders), with no hiccups then just upsize the DB server. Heck, I wouldn't even install the latest sql server on it. Instead, just buy a larger machine, install the exact same OS and DB server (and patch levels) and move your database.
Then look at your architecture to determine what needs to go away and what can be salvaged.
If everybody connects to SQL Server then there is also the option of Service Broker. Unlike other messaging/queueing solution recommended so far it is entirely contained in your database (no separate product to deploy, administer and configure), it offers a single story vis-a-vis your backup/recovery and high availability needs ( no separate backup for message store, no separate DR/HA, whatever is your DB solution is also your messaging solution) and overs a uniform programming API (SQL).
Even when everything is within one single SQL Server instance (ie. there is no need to communicate over network between multiple SQL Service instances) Service Broker still has an ace that no one can match: activation. With activation you eliminate completely the need to poll because the system itself will launch your processing code (will 'activate') when there are events to process. The processing code can be internal (T-SQL procedure or SQLCLR .Net procedure) or external (see external activator).
This is the scenario.
I have multiple clients on our application, and one server.
The server is itself disconnected from the clients, it just downloads some data from the web via a windows service (web services and FTP), processes the data and updates a database to which all the clients are connected and draw data from.
I would like to be able to actively notify the clients, and with a certain degree of granularity, when some downloading occurs (i.e. only the Traders when a price/trade update occurs, or only the Engineers when there's something for them) without polling.
The server should fire up a notification to all the connected clients instead of having them continuously "ask" if there is an update, because in this case I would have to maintain state on all the clients.
I thought about XMPP, with Matrix.
To do so each client has to open a persistent connection with the windows service, but I lack the exact details on how to implement this. MAybe with nodes!
For what I understand XMPP is perfect for what I want to accomplish and gives me the extensibility to grow to some more functionality if I have the need to.
I don't know if to implement my own server or use one of the existing one (I hear jabberd2 has an excellent windows server).
But most important: I need suggestions on A) an XMPP server to run on Windows and B) a C# library. Besides Matrix I have found very few, and above all I need notifications support (pubsub).
For simplicity, I'd consider using a WCF service that implements a long polling technique. This article gives some details on scaling the WCF service efficiently.
For notifications that there is new data in the database, if you are using SQL Server, try SqlDependency. It allows you to set up an event that fires in your code whenever the result of a given query changes. I've used it effectively for just this sort of thing.
I want to design a new distributed application, but I have a few queries that I need some genius advice on, hopefully from you people:
Scenario
I currently support a legacy application that is starting to fall between the cracks.
It is a distributed Client-Server app implemented using .Net Remoting. I can't explain exactly what it does, because I'm not allowed to.......But let's just say that it does LOTS of MATHS. I want to re-design and re-write the application using WCF.
Pre-requisites
The server side of the implementation will be hosted in a Windows Service.
The client side will be a windows forms application.
The server side will perform lots of memory-intensive processing.
The server will spit this data out to multiple thin clients (20-ish).
The majority of the time the server will be passing data to the clients, but occasionally the clients will be persisting data back to the server.
The speed at which the data is transmitted is highly-important, however I'm well aware that WCF can handle fast distribution of data.
Encryption/Security is not that important as the app will run on a highly protected local network.
Queries
Given the information above:
1)What sort of design pattern am I best going with? - Baring in mind I want the server to continually PUSH the newly calculated information immediately to the clients, as opposed to the current implementation that involves the client pulling from the server continuously.
2)What type of WCF binding should I use to ensure maximum speed of data transfer? (as close to real-time as possible is what I'm after)
3)Should I use a class library to share the common objects between the client and the server applications?
4)What is the best way in which to databind my objects on the client side in order to see live updates continually as data changes?
If I've forgotten anything then feel free to point this out
Help greatly appreciated.
1) What sort of design pattern am I best going with?
Based on your comments, you're wanting to transform the current polling mechanism to an event-based mechanism. That is, instead of the client constantly checking the server for results, have the server notify the client when a new calculation result is available.
I would recommend using Juval Lowy's Publish-Subscribe Framework for this.
(source: microsoft.com)
.
This framework is described in detail in this MSDN article. And you can download the framework's source code for free at Lowy's website, IDesign.net.
Basically, the server logic that performs the calculations inside the Windows service is the Publishing Client in the graphic, and the various WinForm applications are the Subscribing Clients. The Pub/Sub Service lives in your Windows service. It manages the list of subscribing clients and provides a single endpoint for your server to publish calculation results to. In this way, your server performs a calculation and publishes the result once to the Pub/Sub Service endpoint. The Pub/Sub Service is then responsible for publishing the result to the subscribed clients.
2) What type of WCF binding should I use to ensure maximum speed of data transfer?
If all of your WCF communication were on a single machine, you'd want to use the NetNamedPipeBinding. However, since you will be distributed, you want to use the NetTcpBinding.
For WCF binding decisions, I have found this chart useful.
3) Should I use a class library to share the common objects between the client and the server applications?
Since you are in control of both the client and server side, I would highly recommend sharing a class library instead of using Visual Studio's "Add Service Reference" feature. For a detailed discussion of this, refer to this SO question-and-answer.
4) What is the best way in which to databind my objects on the client side in order to see live updates continually as data changes?
I suspect this will depend on what controls you use to display the data. One way that immediately comes to mind would be to have your client fill an in-memory data table as each calculation result is received. This data table could then be bound to a ListBox control, for example, that shows the results in calculation order.
This to me looks like you need to implement the Observer pattern, but distributed. Whereby new calculations are made to the service, and WCF just happens to be the mechanism by which you push your notification back to the client.
Generally speaking, you have your business logic housed in a windows service, whereby a type is a Subject (Observable). You could publish an endpoint for clients to register for notifications. This would be a WCF service, with potentially two operations:
RegisterClient(...)
UnregisterClient(...)
When a client is registered with service, it can receive updates, broadly speaking, the when the service has finished calculating a result, it could iterate through all registered clients and initiate a push. The push being a communication through an endpoint on the client.
A client endpoint might typically by
Notify(Result...);
And your server simply calls that when it has new data...
Typically you'd use TCP to maximise throughput.
This is by no means exactly what you should do, but perhaps its a direction to start in?
I'm writing a simple accounting program consists of several C# winform clients and a java server app that read/write data into a database. One of the requirement is that all C# clients should receive updates from the server. For example, if user a create a new invoice from his C# client, other users should see this new invoice from their client.
My experience is mainly on web development and I don't know what's the best way to fulfill this requirement with C#s client and Java servlet server.
My initial though is to run ActiveMQ with Glassfish and use messaging pub/sub method so that updates can be pushed to C# client. I will create different topics like newInvoice, cancelInvoice, etc in order to differentiate the message type. Each message will simply contains the object encoded in JSON.
But it seems to me that this involves quite a lot of work. Given that my user base is very small ( just 3 or 4 concurrent user), it seems to me that there should be some simpler solutions. (I'm not familiar socket programming :) )
I know this is a client-server programming 101 questions but would be great if any experienced programmer can point me to some simple solutions.
The simplest approach here is often to simply use a poll - i.e. have the clients query for data every (your time interval). That avoids a whole family of issues (firewalls, security, line-of-sight, resolution, client-tracking, etc).
With WCF, you can have callbacks on duplex channels (allowing the server to actively send a message to clients), but this is more complex. I value simplicity, so I usually just poll.
Tricks that help here are designing the system to have an inbuilt mechanism for querying "changes since x" - for example, an audit table, perhaps fed by database triggers. The exact details vary per project, of course.
Another option that you might want to look at is ADO.NET Sync Services; this does much of what you ask for, for keeping a local copy of the database up to date with the server - but has a few complexities of its own. This is available (IIRC) in the "Local Database Cache" VS template.
Rather than pushing information from the server to 1:N Clients, would it not be easier to have the clients Poll the server for updates every so often ? Or when the client launches and creates a connection to the server, the server could dynamically generate a new Message Queue for that Client Connection, which the client could then poll for updates?
There are several push technologies available to you, like ActiveMQ (as you mentioned), or XMPP. But if you only have 3 or 4 clients to concern yourself with, polling would be the simplest solution. It doesn't scale well, but that isn't really a concern in your case, unless your server is an 8086 or something 8-)
You may want to take a look at StreamHub Push Server - its a popular Comet server written in Java that has a .NET Client SDK for receiving updates from the server in C#. It also has a Java Client SDK and the usual Ajax/Comet web browser support giving you more flexibility in the future to push data to web, Java and C# clients.