Scenario
I have service written in c#.net.
Now on my production environment I want this service to be on 2 different servers for Loadbalancing or failover of one of the server.
So for instance if one server dies the service keeps running on the other server and users are not affected OR if there is a heavy load on the site users get redirected to different servers.
For users getting on redirected on different servers is not a problem we have the software which can check whether the service is running or not. How to do session management in this case?
How can we achieve this?
Of course you could always spin your own session management service but I don't think that is what you are looking for.
I have experience using NCache for session management and it works well enough.
Microsoft also has Velocity but I'm not sure it's complete yet.
Very old question, but still searchable by Google. Since Windows 2012 there is feature called Clustered Shared Tasks. Probably not mature yet as it is manageble only via PowerShell, but maybe good start. Check this MSDN post. I'm eager to try it myself.
Related
Our company uses a system of which I am the sole developer. It is a C# based desktop application that is run on some 50 workstations or so and all connect to one central SQL Server database.
Our network administrator is now looking at presenting the application through Terminal Services, something that I know nothing about, yet.
As I started Googling around I saw that, apparently, some applications do not work under Terminal Services. MS Paint is mentioned as an example. So this got me wondering, what does a developer need to know to make sure that his/her application works in Terminal Services?
I don't have the time right now to investigate TS in depth but I'm hoping there might be an article somewhere that is written for developers. As in "Things not to do when you develop an application that will be run in Terminal Services".
Terminal Service RemoteApp works pretty well if you application is designed to be multi-user compatible. so you will need to ensure user session related data is not shared, but placed in isolated storage with IsolatedStorageContainment set to DomainIsolationByUser for example.
here are some useful links:
http://www.fmsinc.com/microsoftaccess/terminal-services/remoteapp.htm
https://www.youtube.com/watch?v=Nf20-76dMcg
https://msdn.microsoft.com/en-us/library/3ak841sy%28v=vs.110%29.aspx
I have three applications running in three separate app pools. One of the applications is an administrative app that few people have privileged access to. One of the function the administrative app allows is creating downtime notices. So when a user goes into the administrative app and creates a downtime notice the other two apps are supposed to pick up on there being a new notice and display it on the login page.
The problem is that these notices are cached and being that each app is in a separate app pool the administrative app doesn't have any way to clear the downtime notices cache in the other two applications.
I'm trying to figure out a way around this. The only thing I can think of is to insert a record in the DB that denotes the cache needs to be cleared and the other two apps will check the DB when loading the login page. Does anyone have another approach that might work a little cleaner?
*Side note, this is more widespread than just the downtime notices, but I just used this as an example.
EDIT
Restarting the app pools is not feasible as it will most likely kill background threads.
If I understand correctly, you're basically trying to send a message from the administrative app to other apps. Maybe you should consider creating WCF service on these apps that could be called from the administrative application. That is a standard way to communicate between different apps if you don't want to use e.g. shared medium such a database and it doesn't force you to use polling model.
Another way to look at this is that this is basically an inter-application messaging problem, which has a number of libraries already out there that could help you solve it. RabbitMQ comes to mind for this. It has a C# client all ready to go. MSMQ is another potential technology, and one that already comes with Windows - you just need to install it.
If it's database information you're caching, you might try your luck at setting up and SqlCacheDependency.
Otherwise, I would recommend not using the ASP.NET cache, and either find a 3rd party solution that uses a distributed caching scheme, that way all applications are using one cache, instead of 3 separate ones.
I'm not saying this is the best answer or even the right answer, its just what I did.
I have a series of ecommerce websites on separate servers and data centers that rely on pulling catalog data from a central backoffice website location and then caches them locally. In my first iteration of this I simply used GET requests that the central location could ping the corresponding consuming website to initiate its own cache refresh routine. I used SSL on each of the eCommerce servers as I already had that setup and could then have the backoffice web app send credentials via SSL GET to initiate the refresh securely.
At a later stage, we found it more efficient to use sockets instead on the backoffice where each consuming website would be a client and listen for changes in the data. The backoffice website could then communicate to its corresponding website when a particular account change and then communicate this very specifically. This approach is much more granular and we could update in small bits as needed as opposed to a large chunked update but this was definitely more complicated than our first try.
I'm going to develop a POS system for medium scale company
and the requirement for me is to make all data on time for all of their branches
while in my mind, move the server from local to web would solve this problem
but, i never done any online server for window application
may i know what is the best option for use as secure database ?
such as SQL can handle this well ?
i tried to google but all of the result return is not what i want
may i know what will you do when you facing this problem ?
my knowledge on coding is just VB and CS
also SQL for database
i would like to learn new if there is better option
i hope it is impossible to access by anonymous and it is store secure at back-end only
What you probably want to do is create a series of services exposed on the internet and accessed by your application. All database access would be mediated by these services. For security you would probably want to build them in WCF and expose them through IIS. Then your Windows application would just call these services for most of its processing.
If you design it properly you could also have it work with a local database as well so that it could work in a disconnected manner if, for example, your servers go down.
Typically you don't move the server off of the site premises.
The problem is that they will go completely down in the event your remote server is inaccessible. Things that can cause this are internet service interruption (pretty common), remote server overloaded (common enough), basically anything that can stop the traffic between the store location and your remove server will bring them to their knees. The first time this happens they'll scream. The second time and they'll want your head due to the lost sales.
Instead, leave a sql server at each location. Set up a master sql server somewhere. Then set up a VPN connection between the stores and this central office. Finally, have the store sql boxes do merge replication with the central office. Incidentally, don't use the built in replication, but an off the shelf product which specializes in replicating sql server. The built in one can be difficult to learn.
In the event their internet connection goes dark the individual stores will still be able to function. It will also remain performant as all of the desktop app traffic is purely to the local sql box.
Solving replication errors is much easier than dealing with a flaky ISP.
I would recommend you to check Viravis Platform out.
It is an application platform that also can be used just as an online database for any .NET client with the provided SDK. It has its own generic windows and web clients and some custom web solutions for some specific applications.
You may be using it as a complete solution or as a secure online database backend.
Starting to develop to actual code to my website and wanted to know how do i develop or design the website that is load balance friendly. I read a post on stackoverflow regarding scalability and the selected answer stated: "Make sure you consider load balancing when developing your application". How do I go about this?
Your decision will come down to environment. If this is a product for sale, you will not have any control over the load balancing implementation. This means that "sticky sessions," where a user is bound to the same server for the duration of a session, cannot be guaranteed. Sticky sessions allow just about any application to be load-balanced, but they are not as efficient.
If you cannot guarantee an implementation with sticky sessions, avoid the usage of Session state altogether, or look into a shared-session solution.
1) do not use static fields to store data, statistics, ...
2) use session with care - you can still use in-process with sticky ssessions but I do not like it.
3) Do not rely on the IP of the server
Well, one answer is to reduce reliance upon session variables. It's possible to share session variables between servers via session server, but that means all your servers have a single point of failure on the session server then, plus reducing performance.
Basically, just try to make each page as stand-alone and stateless as possible, and you'll be good.
This might be obvious to most of you, but actually was an issue in our environment when we started to use a load balancer / several web servers: Do not rely on the IP addresses of your web server.
We had a production environment that used a switch and a set of internal IP addresses, including the one of the web server (our products usually run in a closed off environment, not the open Internet). If you have several web servers that becomes a problem.
Make sure you have a development/QA environment where you can test your software in a load balanced environment and see the issues in your code as you develop it rather than waiting until the deployment day.
One thing to take into account is the usage of Session data to maintain state.
As your application subsequent requests can be handled by other servers in the balance line you can not use InProc mode and StateServer mode.
What are the challenges in porting your existing applications to Azure?
Here are few points I'm already aware about.
1) No Support for Session Affinity (Azure is Stateless) - I'm aware that Azure load balancing doesn't support Session Affinity - hence if the existing web application should be changed if it has session affinity.
2) Interfacing with COM - Presently I think there is no support for deploying COM components to the cloud to interface with them - if my current applications need to access some legacy components.
3) Interfacing with other systems from the cloud using non-http protocols
Other than the above mentioned points, what are other significant limitations/considerations that you are aware off?
Also, how these pain points are addressed in the latest release?
our biggest challenge is the stateless nature of the cloud. though we've tried really really hard, some bits of state have crept through to the core and this is what is being addressed.
the next challenge is the support of stale data and caching as data can be offline for weeks at a time. this is hard regardless.
Be prepared for a lengthy deployment process. At this time (pre-PDC 2009), uploading a deployment package and spinning up host services sometimes has taken me more than 30 minutes (depends on time of day, size of package, # of roles, etc).
One side effect of this is that making configuration changes in web.config files is expensive because it requires the entire app package to be re-packaged and re-deployed. Utilize the Azure configuration files instead for config settings - as they do not require a host suspend/restart.
My biggest problem with Azure today is operability with other OS’es. Here I am comparing Azure to EC2/Rackspace instances (Even though Azure as PAAS offers a lot more than them e.g. load balancing, storage replication, geographical deployment etc in a single cheap package).
Even if you consider me as a BizSpark startup guy, I am not inclined to run my database on SqlAzure (Sql2005 equivalent) since I can’t accept their pricing policy, which I’ll have to bear three years after of the BizSpark program. Now they don’t have an option for MySql or any other database. This to me is ridiculous for an SME. With EC2 I can run my MySql instance on another Linux VM (obviously in the same network. Azure gives you the capability to connect to network outside theirs, but that is not really an option)
2nd. This is again is related to using *nix machines. I want all my caching to be maintained by Memcached. With asp.net 4 they have even given us out of the box memcached support through extensible output caching. The reason why I am adamant about memcached is the eco system it provides. E.g.: Today I can get memcached with persistent caching as an add-on. This will even give me the opportunity to store session data with memcached. Additionally I can run map reduce jobs on the IIS logs. This is done using cloudera images on EC2. I don’t see how I can do these with Azure.
You see, in the case of Amazon/Rackspace I can run my asp.net web app on a single instance of Windows Server 2008 and the rest on *nix machines.
I am contemplating running my non hierarchical data (web app menu items) on CouchDb. With Azure I get the Azure table. But I am not very comfortable with that ATM. With EC2 I can run it on the same MySql box(don't catch me on this one :-)).
If you are ready to forget these problems, Azure gives you an environment with a lot of grunt work abstracted. And that’s a nice thing. Scaling, loading balancing, a lot of very cheap storage, CDN, storage replication, out of the box monitoring for services through Fabric Controller etc among these. With EC2/Rackspace you’ll have to hire a sysadmin shelling $150k PA to do these things (AFAIK Amazon provides some of these feature at additional cost).
My comparisons are between azure and Amazon/Rackspace instances (and not cloud). For some this might seem like apples and orange. But azure does not provide you with instances. Just the cloud with their customized offerings…
My biggest problem is/was just signing up and creating a project. And that's how far it got over the last month.
Either I am doing something very wrong, or that site is broken most of the time.
One important challenge is the learning curve, lack of experienced developers, the time it takes to become productive .
This happens with all technologies, but with the cloud there is a fundamental change in how somethings are done.
If your application needs a database, I'm not sure that Windows Azure has a relational database (right now)
Also, there are other cloud computing providers that can offer you more options in configuring your virtual machine for example, it really depends on what you actually need and want.