I have made a WPF Desktop application that fetches data from an API (on every launch) provided by the website over the Internet and updates its UI accordingly. Now I want to change that. I want to put the application's fetching functionality on the cloud which regularly gets data from API and store it in a SQL SERVER (or any) database. Now I want the application on the client side to get data from the database and not from the API itself (can be on every launch or when there is a change in data).
WHATS THE PROBLEM THEN ?
When thinking of a desktop application over the cloud on a windows virtual machine it feels ok and I understand how to implement it.
But when thinking of a web application the server is supposed to respond to client request and then perform some piece of code to give output/Response. Which I don't need I wan't the code to just run weekly or monthly without client asking.
WHAT I WANT ?
I wan't the server to up 24/7 and updating the database every week.
How usually such kind of thing is implemented in general. Let say for example stack overflow. Don't they perform certain task independent of the client on their servers.
Related
i have a bit theoretical question.
When creating web applications, there is difference to desktop applications with working and active connection to database. So im curious if there is some solution, which can provide more desktop-like access to database e.g. transactions on asynchronous requests from client (web browser)?
edit:
So i figured out, that there can be a transaction process of asynchronous request, from client. Is there solution, which can provide it in web apps?
e.g I have assynchronou ajax call, which consist of multiple operations, and i wana to process them as transaction. If everything is okay, operations will be all done. But if one of them fail, just rollback it. Like its in DB. Is it possible?
edit2: maybe im wrong and the issue is not about ajax, but about whole web applications, but i dont think there is a way how to make a asynchronnous request from web client.
Transaction need continuous connection to database. To make it work with web application you need a platform which allow the application to run continuously independent of client request. Java servlet is best fit, php is a no-no. So I asume you will use java servlet.
In java servlet, you can create a db transaction, create an id for it, and then store them in a static variable or in the provided application-wide object, context. Then, return the id to the client.
When the client want to send another request, make it send the id. The application then can locate the transaction variable based on the id. As long as the application doesn't restarted between the two requests, the transaction is still there and active.
Because web application don't know when the user leave the application, you must create a mechanism to check the transactions periodically, and then rollback it if the user leave them for a specified time period.
The database has no knowledge of who is connected outside of authentication.
I need some help understanding how I should architect an application. Basically it has two parts.
The web app (asp mvc): A user logs into the app, records some data and logs off. The data (login info, user recorded data) is stored locally on my server. It is very simple.
The background process: I need a service to receive and send data that is connected with this web app (from #1). I have a 3rd party server that will send user login information (in real time) to my server in which I need to use to update my local DB (this is the same DB that the web app uses for login info). Secondly, I need to run a timed interval process to query the user recorded data plus perform simple logic on it and then send the outcome to this 3rd party server. These steps are all via xml docs.
I am not exactly sure how to attack this problem. I figured I could build a separate web service to do this (it would live on the same server as the web app). Or I could run some sort of webbackgrounder (https://github.com/NuGet/WebBackgrounder) task solution that is attached to my web app. Or lastly I could create a SSIS package to do this. Which route should I go? Thank you for the advice.
I'm designing a database monitoring application. Basically, the database will be hosted in the cloud and record-level access to it will be provided via custom written clients for Windows, iOS, Android etc. The basic scenario can be implemented via web services (ASP.NET WebAPI). For example, the client will make a GET request to the web service to fetch an entry. However, one of the requirements is that the client should automatically refresh UI, in case another user (using a different instance of the client) updates the same record AND the auto-refresh needs to happen under a second of record being updated - so that info is always up-to-date.
Polling could be an option but the active clients could number in hundreds of thousands, so I'm looking for a more robust and lightweight (on server) solution. I'm versed in .NET and C++/Windows and I could roll-out a complete solution in C++/Windows using IO Completion Ports but feel like that would be an overkill and require too much development time. Looked into ASP.NET WebAPI but not being able to send out notifications is its limitation. Are there any frameworks/technologies in Windows ecosystem that can address this scenario and scale easily as well? Any good options outside windows ecosystem e.g. node.js?
You did not specify a database that can be used so if you are able to use MSSQL Server, you may want to lookup SQL Dependency feature. IF configured and used correctly, you will be notified if there are any changes in the database.
Pair this with SignalR or any real-time front-end framework of your choice and you'll have real-time updates as you described.
One catch though is that SQL Dependency only tells you that something changed. Whatever it was, you are responsible to track which record it is. That adds an extra layer of difficulty but is much better than polling.
You may want to search through the sqldependency tag here at SO to go from here to where you want your app to be.
My first thought was to have webservice call that "stays alive" or the html5 protocol called WebSockets. You can maintain lots of connections but hundreds of thousands seems too large. Therefore the webservice needs to have a way to contact the clients with stateless connections. So build a webservice in the client that the webservices server can communicate with. This may be an issue due to firewall issues.
If firewalls are not an issue then you may not need a webservice in the client. You can instead implement a server socket on the client.
For mobile clients, if implementing a server socket is not a possibility then use push notifications. Perhaps look at https://stackoverflow.com/a/6676586/4350148 for a similar issue.
Finally you may want to consider a content delivery network.
One last point is that hopefully you don't need to contact all 100000 users within 1 second. I am assuming that with so many users you have quite a few servers.
Take a look at Maximum concurrent Socket.IO connections regarding the max number of open websocket connections;
Also consider whether your estimate of on the order of 100000 of simultaneous users is accurate.
My organisation (a small non-profit) currently has an internal production .NET system with SQL Server database. The customers (all local to our area) submit requests manually that our office staff then input into the system.
We are now gearing up towards online public access, so that the customers will be able to see the status of their existing requests online, and in future also be able to create new requests online. A new asp.net application will be developed for the same.
We are trying to decide whether to host this application on-site on our servers(with direct access to the existing database) or use an external hosting service provider.
Hosting externally would mean keeping a copy of Requests database on the hosting provider's server. What would be the recommended way to then keep the requests data synced real-time between the hosted database and our existing production database?
Trying to sync back and forth between two in-use databases will be a constant headache. The question that I would have to ask you is if you have the means to host the application on-site, why wouldn't you go that route?
If you have a good reason not to host on site but you do have some web infrastructure available to you, you may want to consider creating a web service which provides access to your database via a set of well-defined methods. Or, on the flip side, you could make the database hosted remotely with your website your production database and use a webservice to access it from your office system.
In either case, providing access to a single database will be much easier than trying to keep two different ones constantly and flawlessly in sync.
If a webservice is not practical (or you have concerns about availability) you may want to consider a queuing system for synchronization. Any change to the db (local or hosted) is also added to a messaging queue. Each side monitors the queue for changes that need to be made and then apply the changes. This would account for one of the databases not being available at any given time.
That being said, I agree with #LeviBotelho, syncing two db's is a nightmare and should probably be avoided if you can. If you must, you can also look into SQL Server replication.
Ultimately the data is the same, customer submitted data. Currently it is being entered by them through you, ultimately it will be entered directly by them, I see no need in having two different databases with the same data. The replication errors alone when they will pop-up (and they will), will be a headache for your team for nothing.
Suppose I have either an ASP.NET displaying my results, or a Silverlight client. And I'd like to show the current status of my server, or embedded device. (pretend the device reads temperature and humidity stats)
How should I send the status information from my device to the front end? Should I poll the device and save the results to SQL, Azure Table, or the like? (Azure is a technology that fits with this project for other reasons. That's why I mention it)
Or should I create a WCF service that polls the device directly and returns the current status.
What makes more sense?
In either ASP.NET or Silverlight you are going to have to poll from the client (web page or Silverlight app) to the backend to get the current status. In ASP.NET I'd look into doing this via an AJAX poll to a service using Javascipt (look at using Jquery or something similar to make this easier).
In silverlight you will need to have some sort of service configured to return the results and poll it using the Timer control running on a seperate thread.
You can also using a "push" binding within your silverlight app. Basically instead of you manually polling the server, the server will send you a push notification anytime it deems it necessary to let the client know of any change.