I am working on asp.net (newbie) and I am trying to understand what it means to do "load balancing" for the web site. The website will be used by multiple users and resources (database, web service,..).
If anyone could help me understanding the concept of the load balance for asp.net web site, I would really appreciate it.
Thanks.
One load-balancing-related issue you may want to be aware of at development time: where you store your session state. This MSDN article gives a good overview of your options.
If you implement your asp.net system using "out-of-process" or "sql-server-mode" session state management, that will give you some additional flexibliity later, if you decide to introduce a load-balancer to your deployed system:
Your load balancer needn't handle session affinity. As one poster mentioned above, all modern load-balancers handle it anyway, so this is a minor consideration in any case.
Web-gardens (a sort of IIS/server-implemented load-balancer) REQUIRES use of "out-of-process" or "sql-server-mode" session state management. So if your system is already configured that way, you'll be one step closer to being able to use web-gardens.
What is it?
Load balancing simply refers to distributing a workload between two or more computers. As a concept, it's not unique to asp.net. Although having separate machines for your database and web server could be called "load balancing" it more commonly refers to using multiple machines to serve a single role, such as having multiple web servers.
Should you worry about it? Probably not. Do you already have a performance problem? Are your database and web server on their own machines? If you do find that your server resources are strained, it would probably be easier to scale up (a more powerful single machine) than out (load balancing). These days, a dedicated box can handle a LOT of traffic if your code is decent.
Load Balancing, in the programming sense, does not apply to ASP.NET; it applies to a technique to try to distribute server load across two or more machines, rather than it all being used on one machine. Unless you will have many thousands (millions?) of users, you probably do not need to worry about it.
Check the Wikipedia article for more information.
Load balancing is not specific for any on technology stack be it asp.net, jsp etc. To load balance is to spread the incoming requests to a web site over more than one server. This is typically done with a software or hardware load balancer. The load balancer sits in front of two or more web servers and delegates the incoming traffic. Although this technique is not limited to web servers. Load Balancing
Enjoy!
I've never used it, but an option is IIS Application Request Routing.
IIS Application Request Routing (ARR)
2.0 enables Web server administrators, hosting providers, and Content
Delivery Networks (CDNs) to increase
Web application scalability and
reliability through rule-based
routing, client and host name
affinity, load balancing of HTTP
server requests, and distributed disk
caching
In a typical web server/database scenario, the db is almost always guaranteed to load up the machine first. This is because dealing with storing data requires more resources. Before you even start looking at load balancing your web server, you need to think about how to load balance the database.
Spreading one database across multiple servers is a lot harder than load balancing a web server. One of the techniques that can be used is sharding (or horizontal partitioning). This is where some records are stored on one server, and other records - on another server. For example records with ID 1-900000 are on server 1 and records 900001- are on server 2.
In comparison to DB load balancing, spreading the load across multiple ASP.NET servers is not overly complicated. Most of the session issues can be easily mitigated by using out of process session and/or never talking to Application.Cache directly. Data load balancing on the other hand is hard and requires a lot of planning and trial and error. In most cases, talking to a load balanced DB requires using an ORM which supports it (e.g. NHibernate) or your own Data Access Layer. The reason being is that you need to take out establishing a connection from the code that uses the database, so that the decision which DB to talk to is handled in one place.
the exact solution is to save session into the SQL Server with Stored Procedure. To read session call 'SessionCheck' stored Procedure.
I'd add that it really isn't something to worry about. By the time you need a load balancer, you can probably afford one of the neato newfangled ones with sticky sessions so you don't even have to deal with the session boogeyman.
Related
Lets say I have one WCF service that is running on one server.
Now we introduced some caching on the wcf service for performance reason.
Now if I want to do some load balancing .... is there some existing solution that will allow my cache to also be synched when it is living on different servers ???
How do we deal with these sort of issues?
Maybe a solution is to create a seperate CachingService that will be hosted on another server ... but then again if I want to load balance that service ... I'd need to somehow sync those cache that resides on different machines ...
Or maybe it doesn't event makes sense to load-balance the caching servers but only your wcf services???
Yes, there are many solutions/product that (usually) sync cache between servers (memcached, ehcache and more). I personally found that in case of closely located servers referenced cache performs better. That is cache where (possibly multiple) cache servers share the load and store objects on first "requested from" basis and then share references to the objects between all cache servers.
Our infrastructure team has configured a a load balancing using Radware. Basically we have 3 web server that are load balanced.
Before we go live I would like to test and make sure that load balancing is working. How do I test the following:
3 servers are load balanced and requested are evenly distributed. (Any automated tool exists?)
Asp.net InProc session are working.
You can test by first generating an artificial load on your site (with any one of a number of load generators). Then have a look at the Windows Performance Counters for each site: things like HTTP requests per second and CPU use would be reasonable high-level metrics.
Yes, there are automated tools, but they usually require quite a bit of setup, and the better ones charge a fee. Perf counters are fast, easy and free.
As #swannee said, InProc sessions won't work in a load-balanced scenario unless your load balancer is configured to use sticky sessions. It's better to use SQL Server sessions with load balancing.
FWIW, you can test your software in a "mini" load balanced scenario on a single server by enabling IIS web gardens (multiple worker processes), from the AppPool config dialog.
Can you look in the IIS server logs to see how many hits each server is getting?
http://msdn.microsoft.com/en-us/library/ms953324.aspx
Also, unless you are using sticky sessions, you are going to have problems with InProc session. It won't work on a server farm (unless as stated you have sticky sessions turned on). If you don't have sticky sessions, you'll be able to tell real quickly that your session is being lost between requests with just some manual testing.
Our organization makes a series of ping and advanced status pages. These pages are monitored by our load balancers so it can take out unhealthy nodes in the event one node loses a connection to a database server or the node itself is having issues.
Our ping pages spit out the server name that you're connecting to and the status. They are avaliable by the common server names themself, like server01.application.com/ping and server02.application.com/ping but more important, they all answer on application.com/ping.
Refreshing the page will show us a new connection (you can see the server name change).
To test load you could use WCat, it's not the easiest tool to setup and script but it works.
To test sessions. you'll need to build out some pages that you can do load testing on to test sessions
So we're scaling out our application to have two Web servers, and will most likely need four or five in the next year or so if all goes well.
I'm aware of sharing session state between servers with SQL Server and the ASP.NET state server. However, I'm a little concerned about the single-point-of-failure with the ASP.NET state server, and as we don't use SQL Server for anything else I'd rather avoid that provider, too.
What are my alternatives? What custom state servers are out there that are light-weight, can support fail-over between multiple machines, and don't require the licensing overhead of SQL Server?
Take a look at either:
Memcached: http://memcachedproviders.codeplex.com/
or,
AppFabric: http://msdn.microsoft.com/en-us/library/ee790859.aspx
Both are free.
There's also scale out state server, but you have to pay for it: http://www.scaleoutsoftware.com/products/scaleout-sessionserver/
We have a web-application product that we sell to companies that is hosted at our servers.
The product contains couple of web applications, windows services and SQL server db.
Right now we have only one client that uses our product. We have two servers - one for the web apps and services and other for the db.
In order to add the product to another client, we have to 'duplicate' all the apps and db and run in separately.
As we started expanding and some companies will require more server power then others, I need to plan the servers infrastructure.
Having two servers for each client sounds ridiculous. Hosting costs will be huge. What will happen when I'll have 10 clients? And probably some servers will take more power than others, leaving servers using 30% from their capacity while others use 70%.
One thing I really care about is separating the DB from each product so in case of server compromise, only one db will be at risk.
So... I thought about Virtual Machines...
Does it sounds right?
Do I need two super servers to hold virtual machine instances? (one for web and other for db?)
What about Load balancing / etc..?
Will it require more maintenance time only because I use virtual machines?
Are there any hardware recommendations?
Any help will be appreciated
Many thanks
Virtual Machines is definitely the safest way to separate clients and will allow you the flexibility to allocate a specific percentage of resources to specific clients.
However, using separate processes on the same physical machine will perform better (but not always significantly) and will allow more dynamic use of resources (i.e., if one spikes, it will use the resources it needs). This setup will not allow you to control the resource allocation nearly as easily though. You'll also have to build your own monitoring tools to see and analyze what processes (clients) are using what resources (piggyback on perfmon).
Using separate processes also is dangerous if your application wasn't designed for this. Anywhere the application caches data on the file system or accesses anything besides memory and the database needs to be thoroughly scrubbed to make sure data from clients is not co-mingled or shared.
Separate virtual machines is more work to manage--each one is pretty much like it's own computer. So you have to manage all the VM's plus the physical machine.
You may also want to consider hosting in a more dynamic environment like Amazon AWS or Microsoft's Azure which will allow you to more easily scale up/down as necessary than a VM at a traditional host.
I would like to ask you what is the best setup for a following application:
ASP.NET 3.5 Web site - used as a presentation layer, a lot of AJAX and JS. Will not hit the server a lot.
ASP.NET WCF - sevice providing all data to the application. It's responsible for validation, data modeling / preparing and communication with the DB Server.
Database - SQL Server 2005 Std, some logic is coded on the server side as stored procedures. Some of the logic can be a bit time consuming. In my opinion it's the most resource consuming part of the app.
The website can have up to 1000 users per minute. We can have up to 4 servers in the following configuration: Intel Bi Xeon Quad 8x 2.00+ GHz, 16 GB RAM, SSD or RAID drives.
What is the best way to place parts of the application on the physical servers? Will they handle this kind of load?
The less scalable place in any application is database server, you can add more web and application servers but you can't replicate DB with the same ease so you will benefit in a long run if DB will not contain any logic especially any long running logic. In a lot of the applications limiting factor is not cpu but memory think about user sessions if you store 1mb of data per user you applications will be able to support 64,000 silmantanius user sessions with you machines it may be sufficient or not. Both problems can be mitigated by using application level caching but this can cause it own set of problems because now you faced with stale data. To scale session based sites you will need to use smart load balancer solution that supports sticky sessions, for your loads most likely you will need hardware load balancer.
In the application you describe, I suspect that thread management is going to be a big issue. Throwing hardware at the problem may not be the best approach.
In terms of partitioning, it depends on whether you can leverage things like caching and cache notifications. If every call to the app has to hit the DB and run a lengthy stored procedure, then you may want to have more DB machines and fewer front-end web servers.
This is a big subject. In an attempt to provide a reasonably comprehensive answer to exactly this kind of question, I ended up writing a book about it: Ultra-Fast ASP.NET: Build Ultra-Fast and Ultra-Scalable web sites using ASP.NET and SQL Server.