Right now, my site is served by a single server, but I anticipate the need to increase my server capacity, soon. Instead of splitting my websites up among multiple servers and having to manage sessions across servers, I want to have multiple web servers all with the same code base on them and use router based round robin load sharing to distribute users to each server. And once a user hits a web server, have him stay with that web server throughout his/her whole session. To my knowledge, I don't need to have any special asp.net code to facilitate this.
Does anyone have any caveats or comments for this approach?
What you are talking about is called sticky sessions or session affinity. If your router supports this, then you are golden.
The only caviat is that the load balancing won't be perfect. If you have a few high-load users who all end up randomly on the same server, they will staty there until the sessions end.
I have implemented this kind of load balancing where I work, and it requires no special asp.net code to implement.
Most (perhap all) load balancers do have the ability to enforce "sticky" sessions where users on the same IP are directed to the same web server on every request. There is no code change required to accomplish this. There are two caveats that come to mind:
Using sticky sessions will mean that the traffic load will not be distributed as evenly as it would if you were not using sticky sessions. However, the distributionshould be"even enough" IMO.
There will be a very small percentage of users using proxy servers that may come in on different IPs on different requests. These users may experience "odd" behavior as they get passed to different servers.
Another characteristic of this configuration is that if one your servers go down the sessions of the users on that server will lose their session as well. I think this is one of the most commonly used setup since it does not require any development effort if the router supports sticky session or session affinity.
As others have mentioned, you should be able to turn on Sticky Sessions on your load balancer, that should take care of most of the "stay on one server" issues for you.
However you will want to ensure you have put settings in place to cope with a user landing on the wrong server mid session - Sticky Sessions are usually based on IP address, and users IPs can change mid session if you're unlucky, or a server may go offline, and the user will be directed to the other server.
You should make sure that your MachineKeys are the same across all servers - this will ensure that you can decrypt the viewstate correctly on all servers.
If you own the servers, you can do this in the machine.config, otherwise you can set it at the application level in the web.config, more details can be found in this how to:
Configure MachineKey in ASP.NET 2.0
There are some slight differences if you're running on IIS 7.5 - Tess Ferrandez has more details in a recent post "Forms authentication fails after installing IIS 7.5".
The other thing you'll probably want to do is move your sessionState from InProc to either Sql or StateServer.
Related
Recently to allow concurrent requests at some level and to increase the performance, we enabled EnableSessionState="Readonly" for one our .aspx page for read only access for session data.
I would like to know enabling this in web farm, will this effect any data loose or any other impact in server or user ?
Current Web Farm Settings:
Lets say We have 4 servers.
1. Lets say User A, requests for the page http://example.com/StudentDetails.aspx, this request hits Load Balancer.
2. Load Balancer based on traffic transfer the request to any 1 from 4 avialable servers.
3. Each server Has InProc Session State mode enabled.
4. We ensure that the same server handles subsequent requests from the same client.
Any help would be great.
What impact have you anticipated?
You simply set it read only in one single page. If, as you mentioned, you aren't even sharing sessions between your servers, then effectively for session purposes you don't even have a farm. You just have 4 individual servers. There's no impact on the farm because there's no session sharing.
If you do start sharing sessions as I suggested in the comments, then I still think the impact will be minimal if any at all. Read-only access should lead to less blocking (e.g. as might occur if the user is requesting two session-enabled pages concurrently) but that's all.
Basically my question is i have a website which was developed around 3 years ago, while development it was proposed that this site will be used by few people on internet.
But now it seems like many users are accessing the website. So we have planned to create a Web sever Farm where we have multiple servers for our website.
major problem in development is old website used InProc Session state and now since we are upgrading to multiple servers we want to change InProc to Outproc i.e StateServer Session State.
Can you guide me on this upgrade and how can it be achieved in simple and easy way rather than changing the coding on each pages wherever sessions are used.
What you going to have here is that you move your site to many web servers and the actual issue here is "how to keep the same state for each user regarding the server".
There are two options.
First option is to setup the router that split the users to the server, to use the "Sticky option", meaning that each user is stick for his session to one server, and one only. In this case it did not matter if you use inproc or sql server session, as long as the router make good job. This is the case of course that you do not use any other database for common data.
Second option is to use an sql server and move the session to the server, but here the server must be on one server and the others server's gets his session data from this one. Also you setup on web.config the same key machine for all web servers.
So for this case you need.
To setup a common/shared SQL server on one server
To install on this the session database (actually run a script from asp.net)
Setup the web.config to use this database as session
Setup the web.config to have the same machine key.
In the case that you use a database for other data, then you place this database together with the session database, and you make a share connect to that database also. The point here is that the data must be live on one computer, and the other computers connect to this main one for the data.
We have a web application running on ASP.NET 3.5. It is viewed by the world as one URL but in reality there are multiple IIS boxes hosting the application controlled by a load balancer.
My problem is that it is a sensitive application with strict security controls around it, and that post authentication if you open another browser to the same application and log in as someone else, the second login overwrites the first logins' session id value in the cookie, and then the first window crashes.
Any idea how I can get around this?
The session ID is placed in the cookie. If another browser window is opened and starts a second session the ID in the cookie will be replaced.
Also, logins should not be controlled via the session cookie. There is a Forms Authentication cookie for that purpose which is more secure as I recall.
Most web applications only allow one session per PC. Try logging into Yahoo Mail, Amazon or Ebay twice on the same machine and you will find the same problem. So ASP.NET is pretty much designed around the idea that there is one login per PC. Although, if you have multiple browsers installed on a machine, you can generally log into apps more than once because each browser keeps its own cookie collection.
edit: You might want to try cookieless sessions, in theory they might allow multiple sessions per PC, although I haven't tried it. But cookieless sessions come with plenty of problems and limitations of their own.
In short, there may be some hacky way to do what you want to do, but it will probably be fiddly and cause other problems elsewhere, because what you are asking for goes against the grain of ASP.NET's core design.
I have posted the following question concerning ASP.NET web farms.
How to create an ASP.NET web farm?
Guys recommended using Network Load Balancing (NLB) as a primary way of creating a web farm.
However, Wikipedia says that "NLBS is intended for ... stateless applications". Our web application, however, is absolutely "stateful": it is a closed site to which users will have access by login and password, and information for every user will be different: people will see their own trades and operations.
Should we still use NLB in this scenario?
Thank you.
Should we still use NLB in this scenario?
Do not see reasons why not if you follow the guidelines.
The web application is by nature stateless, so even if your users should log-in it does not make the application stateful.
Couple the things which ARE stateful in ASP.NET are:
Session State
Cache
which can be configured appropriately in a WebFarm.
Here is an example on how to configure the NLB.
You can still use a NLB, but you need one that supports Sticky Sessions, meaning that it will always route traffic from a certain client to the same web server. Not the best solution in terms of load balancing, but at least allows you to grow to multiple servers.
I think load balancing is still desirable. You just need to set it up so sessions are "sticky": once a session is open:
http://technet.microsoft.com/en-us/library/bb734910.aspx
Absolutely, yes. There are strategies you can employ to maintain state between servers in your farm. The machineKey settings should be the same for all webservers in your farm so that auth tickets are valid between machines.
http://msdn.microsoft.com/en-us/library/ms998288.aspx#paght000007_webfarmdeploymentconsiderations
There are a few options for managing session state between your webservers:
http://msdn.microsoft.com/en-us/library/z1hkazw7.aspx
http://support.microsoft.com/kb/311209
We have 5 balanced web servers with various websites.
What I am trying to achieve is to ensure a single login.
i.e. the same user account cannot login to the same website more than once at any given time.
The method i'm considering for solving this, is to share session amongst the servers so I can control which session is assigned to which account. I can then have control over my logins. If a user logs in and there is already a session assigned to their user account, I can just expire the first session or reject the login.
I don't want to lose the benefit of the balanced servers, so using a single Sql Server as my session state server, or a single server to handle login is not an option.
Is distributed session (something like Scaleout Sofware) the correct approach to achieve this?
Or is there another mechanism to handle single login that i'm blissfully unaware of?
You have two set of problems here:
1) Allowing just one connected user in a web farm scenario
2) Detecting user logoff
To solve the first the only solution is a central storage for some kind of user state, using a central server to store the ASP.Net session or some other kind of centralized user state. This central storage can be SQL Server using the native management of session state (btw also Oracle, from Oracle 11, can support session storage), the AspState service or an external solution, like ScaleOut (as you said) or its open source alternative memcached (see https://sourceforge.net/projects/memcacheddotnet/). Or you can design a simple centralized web service that check active logins against a SQL Server database, this way you can also quickly create reporting tools about logged on users and so on.
Real problem, in my opinion, lies in the second part, that you need to maintain the different "wrong logoff" scenarios that are available in a web world (like closing the browser due to a crash or shutting down applications without logging off), giving you application some way to gracefully work with user that has an old session enabled (as you said simply expiring the first session can work).
Keep also in mind that using a state server like SQL server will not make you loose the balanced servers, if's the way of working to have a web farm environmet and sharing session, only problem lies in performance (if session state become large) and the cost involved in using SQL Server if you do not already have the proper license.