Web farm is used for multiple request and multiple user using switching among them.
Web Garden creates worker processes for every processor individually for one user.
Is it possible to use worker process as a switch and convert it into Web Farm that can allocate multiple processor on bases of algorithm?
From my point of view (and please correct me if I mistake)
the practical diferent betwing web farm and web garden is that the web farm is a plan running on many computers, and web garden is a plan running on a single machine.
You do not need from my point of view to try to convert web garden to web farm, is with out any point. (please correct me if I mistake)
If you have one machine, and you open more than 1 worker process on Web Garden iis settings, then you only need to make your setup running as web farm, have one database connect, use mutex or other lock for be sure that 2 or more worker process are synchronize together.
In my application I have use them both and my only issue is the synchronization of the data.
Related
I understand that having one app pool per app helps isolate errors in one app from impacting other apps.
However, sometimes apps are configured to share the same pool.
Is there any benefit to this, other than having the (memory?) overhead of one-app-per-pool?
Does this configuration permit scenarios not possible in one-app-per-pool?
Maybe in-pool inter-process communication? (Or rather, inter-app communication, since the apps share the same w3wp worker process)
To my knowledge there is no inter-app communication benefit (specifically, if you have two applications in the same pool which both happen to load the exact same dll file, it will still load it twice, you're not saving there).
The advantage is in managing resource limitations. Letting two apps share 500MB is more flexible than each app getting its own 250MB (or my personal favourite way of describing this, you're better off with 2 bathrooms for 4 people, than 1 bathroom for 2 people). You lose isolation, but you gain some headroom on resources (assuming the two applications peak at different times).
I'm troubleshooting restarts in an ASP.NET application. The application is restarting about 20 times a day. We strongly suspect one part of the application because the restarts began when this particular feature when into production. I've added some logging to those pages using the log4net library, but I'm having trouble interpreting the logs.
When an ASP.NET application is running in an Application Pool, does only a single instance of that application run, or will multiple instances of that application run? I know several worker process threads will be spawned. What is the relationship of the worker process threads to the application(s) running in the App Pool?
I am thinking that I may not be interpreting the results correctly if there are multiple applications logging to the same log. If one is restarted but the other is not, the logs aren't really telling me much about what was happening when the restart occurred.
UPDATE 1
Looking at this page, I find the following information:
An application pool defines a group of one or more worker processes, configured with common settings that serve requests to one or more applications that are assigned to that application pool. Because application pools allow a set of Web applications to share one or more similarly configured worker processes, they provide a convenient way to isolate a set of Web applications from other Web applications on the server computer. Process boundaries separate each worker process; therefore, application problems in one application pool do not affect Web sites or applications in other application pools.
But I am still confused. I know from experience that I can assign two entirely different applications to use the same App Pool. Does that mean that exactly two worker processes will be spawned? Or can there be multiple worker processes spawned for the first app, and multiple worker processes spawned for the second app? If a problem happens in one worker process, can it take down every application running in that App Pool?
UPDATE 2
From this page about using WinDbg, I found this information (emphasis mine):
In IIS 5.x, there is only one Aspnet_wp.exe worker process and one debugger thread. Consequently, only one debugger can be attached to the Aspnet_wp.exe process at a time. This can pose a problem if you're dealing with multiple Web applications on the same machine. In IIS 6.0, you can coerce an AppDomain to run in a separate application pool. (For more information, see "IIS 5.x Process Model" and "IIS 6.0 Process Model" in Chapter 1.) Separate application pools provide multiple W3wp.exe processes. Multiple debugger threads are created in these processes (one in each), allowing you to debug more efficiently.
This sounds to me like each App Pool gets one w3wp.exe process. Am I interpreting that right? And if so, does that still apply in IIS 7.5?
Yes, each application pool is typically a single process1, but can contain multiple threads. You can assign multiple sites to an application pool, and those sites will all run under the same process, however they will run under different "app domains", which are security contexts that separate the code of one site from another, even if they're running on the same app pool.
Two users hitting the site at the same time can run on different threads, meaning they can run concurrently. That means any logging can have values interspersed. You might want to add a session value to your logging so you can sort based on session.
App pool restarts (recycling) are normal, 20 restarts in a day does not seem unusual. They can happen multiple times per day, and IIS controls when app pools are restarted. It does this whenever it feels it needs to clean up the pool.2 Your applications should be written in such a way as to recover gracefully from this (ie, do not keep anything in session that cannot be easily recreated if the app pool restarts).
The app pool can also restart when an unhandled exception occurs in your app. In that case, you want to address the cause of this. Such exceptions are usually logged in the event log.
1 – While you can configure an application pool to have multiple worker processes (this is known as a Web Garden), this is not a typical (nor generally recommended) configuration in my experience.
2 – Note that using IIS Manager you can configure an application to log recycle events to the Windows Event Log. You can also use IIS Manager to set the threshold for when several of the different types of recycle events occur.
Can anyone explain the differences, in IIS, between application pools, worker processes and app domains? Also, how do they work together? I've read a couple of articles but it's still a little confusing.
Does each website created in IIS becomes an application?
Is each application associated with one worker process?
Where do app domains come into the picture?
I try to say them with other words.
In a server you can have many asp.net sites that runs together. Each one site is an app domain.
You must assign to each of them one application pool. Many application domains (sites) can have the same application pool, and because they have the same application pool they run under the same processes, and under the same account - and they have the same settings of the pool. If this pool restarts, then all sites under that pools restarts.
Now each pool can have one or more worker process. Each worker process is a different program that's run your site, have their alone static variables, they different start stop calls etc. Different worker process are not communicate together, and the only way to exchange data is from common files or a common database. If you have more than one worker process and one of them make long time calculations, then the other can take care to handle the internet calls and show content.
When you assign many worker process to a single pool then you make the called web garden and your site is like to be run from more than one computer if a computer is one processing machine.
Each worker process can have many threads.
How the more worker process affect you:
When you have one worker process everything is more simple, among your application all static variables are the same, and you use the lock to synchronize them.
When you assign more than one worker process then you still continue to use the lock for static variables, static variables are not different among the many runs of your site, and if you have some common resource (e.g. the creation of a thumbnail on the disk) then you need to synchronize your worker process with Mutex.
One more note. Its sounds that when you make more worker process then you may have more smooth asynchronous page loads. There is a small issue with the session handler of asp.net that is lock the entire process for a page load - that is good and not good depend if you know it and handle it - or change it.
So let talk about one site only with many worker process. Here you face the issue that you need to synchronize your common resource change with Mutex. But the pages/handlers that use session they are not asynchronous because the session locks them. This is good for start because you avoid to make this synchronization of many points your self.
Some questions on this topic:
Web app blocked while processing another web app on sharing same session
jQuery Ajax calls to web service seem to be synchronous
ASP.NET Server does not process pages asynchronously
Replacing ASP.Net's session entirely
Now this session lock is not affect different sites.
Among different sites the more worked process can help to not the one site block the other with long running process.
Also among different sites the more pools also can help, because each pool have at least one worked process, but remember and see by your self using the process explorer, each working process takes more memory of your computer, and one big server with 16G memory and one SQL server can not have too many different worked process - for example on a server with 100 shared sites, you can not have 100 different pools.
One IIS server may have multiple application pools.
One web application binds to one application pool.
One application pool may have more than one worker process (when Web Garden is enable).
One worker process can have multiple app domains. One app domain lives only in one worker process.
One app domain may have multiple threads. One thread can be shared by different app domains in different time.
The meaning to ASP.NET developers: to make your web site scalable, don't use in-proc session and don't use static class variable lock for synchronization.
Yes, though not every application is a website. You can have an application that is nested under a website.
Yes, every application has to have one worker process (application pool), though one application pool can server several applications. A single web application can be distributed (web garden/farm) meaning that it will run in multiple processes.
Each process will run in its own app domain (every application pool is a separate app domain).
From MSDN.
Create a Web Application:
An application is a grouping of content at the root level of a Web site or a grouping of content in a separate folder under the Web site's root directory.
Application Pools:
An application pool defines a group of one or more worker processes, configured with common settings that serve requests to one or more applications that are assigned to that application pool. Because application pools allow a set of Web applications to share one or more similarly configured worker processes, they provide a convenient way to isolate a set of Web applications from other Web applications on the server computer. Process boundaries separate each worker process; therefore, application problems in one application pool do not affect Web sites or applications in other application pools. Application pools significantly increase both the reliability and manageability of your Web infrastructure.
From the source link:-http://weblogs.asp.net/owscott/archive/2007/09/02/application-vs-appdomain.aspx
An application is an IIS term, but it's one that ASP.NET utilizes.
Essentially it creates a sandbox, or a set of boundaries to separate
different sites, or parts of sites, from the others.
An AppDomain is a .NET term. (In IIS7, AppDomains play a larger role
within IIS, but for the most part it's an ASP.NET term)
The worker process is used to process the request of the web application.
I saw this question:
How many users on one azure instance before I hit performance issues?
Which discusses how many users an azure instance could support for a webpage. I'm wondering if this would be any different for a webpage vs webserver that client applications (such as mobile phones) are call into, to get data. For example, if you have a single azure webrole running that exposes a REST enpoint, how many devices could call into the service before it starts to buckle under pressure?
How long is a string? :-)
If your app computes one million digits of pi on each web request, it will probably handle fewer concurrent web requests than an app that replies to each web request with "hello world."
(This is another, blunter, version of David's answer.)
A Web Role instance is merely a Windows 2008 Server R2 (or SP2) virtual machine of a given size (1-8 cores, 1.75-14GB usable RAM, 100-800Mbps network). You can run web sites, different web servers (tomcat, for example), WCF services (through IIS or standalone ServiceHosts), etc.
Scaling is going to depend heavily on the app itself: Is it CPU-constrained? Network-constrained? Do you have queue-based workload and your queue backlog is growing?
Sometimes it's critical to scale up to larger VMs, just to handle one of the constraints mentioned. It's always wise to pick the smallest VM size to run in a baseline mode (e.g. 1 or 2 users), then scale out to more instances as needed.
It's important to identify the key performance indicators (KPI's) for your app. You can then automate your scaling, with something like the Autoscale Appliction Block (WASABi).
Here's a reference page with all VM sizes, with details about CPU, local disk, network bandwidth, and RAM.
for IIS7
Does a webapplication run faster when Maximum Worker Processes is more than one?
By increasing the Maximum Worker Processes over 1 you're creating a Web Garden. So the short answer is: likely no... unless:
To quote Chris Adams an ex IIS PM's article I have flowers... should I get a Web Garden?:
Web gardens was designed for one single reason – Offering applications that are not CPU-bound but execute long running requests the ability to scale and not use up all threads available in the worker process.
The examples might be things like -
Applications that make long running database requests (e.g. high computational database transaction)
Applications that have threads occupied by long-running synchronous and network intensive transactions
The question that you must ask yourself -
What is the current CPU usage of the server?
What is the application’s threads executing and what type of requests are they?
Based on the criteria above, you should understand better when to use Web Gardens. Web Gardens, in the metabase, equals the MaxProcesses metabase property if you are not using the User Interface to configure this feature.
cscript adsutil.vbs set w3svc/apppools/defaultapppool/maxprocesses 4
I hope that I get some mileage out of having this blog and more importantly I hope it helps you understand this better…
You may want to look at "What is Web Garden?" from Deploying ASP.NET Websites on IIS 7.0 [codeproject.com] which says:
By default each Application Pool runs with a Single Worker Process (W3Wp.exe). We can assign multiple Worker Processes With a Single Application Pool. An Application Pool with multiple Worker process is called "Web Gardens". Many worker processes with the same Application Pool can sometimes provide better throughput performance and application response time. And each worker process should have their own Thread and Own Memory space.
WebGarden is faster than single worker process in case if application contains locks that prevent its parallelization. For example, GDI+ based image processing.
See this and this questions for more info.