I can understand Appdomain concept, but small doubt is
One Process -> many application domain,
ok now,
when a application domain is created ? while making request or at time of hosting in IIS.
Again created Appdomain is One to one relationship with asp.net web Application..?
Could you please clear this, I want to know when appdomain created by CLR?
Thanks
karthikeyan
I'd say an AppDomain is created per ASP.NET web application, and is launched when the first request comes in and there is no AppDomain already instantiated for the current path.
Obviously there are IIS configurable idle times for when AppDomains in an AppPool (many to one) are being shut down.
when a application domain is created ?
I suppose when starting up IIS after you have set up virtual directories and uploaded your project files. Or maybe during the first incoming request.
Another thing to remember is that an application domain can be destroyed and recreated during operation. If your application has consumed too much server resources (memory), the application domain can be recycled and then recreated again.
When IIS6 starts up, it starts the App Pools. Each App Pool is a w3wp.exe process. Each process then creates its AppDomains for each associated ASP.NET application and triggers the Application start events on each.
One AppPool is a w3wp process and in this it makes AppDomain for each application on various scenarios like the Application's resources are more consumed (restart of appdomain) or the files like web.config etc are altered or a version of DLL is added.
Related
Ok so I understand how app pools work and what they do but I am wondering what exactly the app pool is, I am thinking at the moment that it is just information the metabase or some config file for use with http.sys?
I suppose another questions is, who or what spawns the worker process when a request is made?
thanks
The confused
First you can see the application pool as the program that actually is one with your pages and runs them. So what ever you make programmatically on your pages are done using the application pool.
For example:
user request the page a.aspx
IIS see that is asp.net page and assign it to one app pool
application pool see the a.aspx, check if is complied, and runs it - run your code.
Second you can see the big view, that there are many web sites lives together on one server and application pool is handle one or more web sites together.
Now, a web application can be run on one application pool, or on many application pools at the same time on the same server (this is called web garden). An in each of that you can run many threads.
Now for more details you can read the official microsoft pages.
We are using IIS7 to host an asp.net web-based application.
In this environment administrators and developers can deploy code to the application on a regular basis.
The new code or app goes as a DLL to the ASP.NET bin folder. Upon deployment of the new DLL, IIS restarts the process, impacting (slowing down) all online users.
Is there a way to configure IIS to run the process in the background and once ready make the switch from old state into new without impacting the users?!
Thanks in advance for your feedback!
IIS already does this, that's what recycling is all about. IT's loading the DLL's while the old version of the application is still running. only after this is completed the recycling is complete.
However loading the DLL's is only part of getting web applications ready, there might also be initial loads like loading/caching the user db etc.
These actions are not part of the recycle process, they happen after all DLL's reloaded and the recycling is already completed.
A while back I ran into this issue with an application that had a huge startup time due to heavy db activity/caching during startup. So I was interested if there is some functionality that allows us to execute code before the recycle is marked as completed, so that the application is first considered recycled when everything is ready to run. Basically what I wanted is some kind of staging functionality.
I was in contact with the IIS team regarding this issue, sadly they told me that no such functionality exists, nor is it planned.
To solve this you could try do the following:
Use alternating deploys:
You setup 2 Websites with separate application pools. One of them is the LIVE website the other one is the STAGED website. If you want to deploy changed you simply deploy to the STAGED website. After everything is loaded/cached etc. you switch the URL settings of the web applications to reroute incoming requests from the LIVE to the STAGED one. So the LIVE one becomes the new STAGED and the other way around. The next deploy would then go to the new STAGED again and so on.
UPDATE
Apparently they have created a IIS Module that provides this functionality by now:
IIS Application Warm-Up Module for IIS 7.5
The IIS team has released the first beta test version of the
Application Warm-Up Module for IIS 7.5. This makes warming up your
applications even easier than previously described. Instead of writing
custom code, you specify the URLs of resources to execute before the
Web application accepts requests from the network. This warm-up occurs
during startup of the IIS service (if you configured the IIS
application pool as AlwaysRunning) and when an IIS worker process
recycles. During recycle, the old IIS worker process continues to
execute requests until the newly spawned worker process is fully
warmed up, so that applications experience no interruptions or other
issues due to unprimed caches. Note that this module works with any
version of ASP.NET, starting with version 2.0.
For more information, see Application Warm-Up on the IIS.net Web site.
For a walkthrough that illustrates how to use the warm-up feature, see
Getting Started with the IIS 7.5 Application Warm-Up Module on the
IIS.net Web site.
See:
http://www.asp.net/whitepapers/aspnet4
If you use ASP.NET 4 Auto Start feature:
You can still choose to auto-recycle the worker processes from time to
time. When you do that, though, the app will immediately restart and
your warm up code will execute (unlike today - where you have to wait
for the next request to-do that).
The main difference between Warm Up and Auto Start feature is that the Warm Up Module is part of the recycling process. Rather than blocking the application for requests, while running the init code.
Only thing you get by using the Auto Start feature is that you don't have to wait for a user to hit the page, which does not help your case.
See the Gu's blog post:
http://weblogs.asp.net/scottgu/archive/2009/09/15/auto-start-asp-net-applications-vs-2010-and-net-4-0-series.aspx
UPDATE 2:
Sadly the Warmup Module has been discontinued for IIS 7/7.5:
http://forums.iis.net/t/1176740.aspx
It will be part of IIS8 though (It's now called Application Initialization Module):
http://weblogs.asp.net/owscott/archive/2012/03/01/what-s-new-in-iis-8.aspx
UPDATE 3:
As pointed out in the comments the Warmup Module resurfaced for IIS 7.5 as Application Initialization Module for IIS 7.5 after IIS 8 was released:
http://www.iis.net/downloads/microsoft/application-initialization
The first part of ntziolis answer is a wee bit inaccurate. The worker process isn't being recycled or restarted, it just keeps running. If this were the case, then in shared pool environments you would have sites knocked out every time a new one was deployed.
When you deploy a new ASP.NET application it's the site's "Application Domain" within the worker process is torn down, not the pool process.
In addition pool recycling is a completely separate concept to deployment
At this point in time in the commercial life of ASP.NET, during a deployment, a site will be in an inconsistent state until all of the site is deployed. There is still no good story about this from Microsoft at this time for single site on a single server deployments.
This is why ASP.NET has the special App_Offline.htm page. It's there so you can enable that page, deploy and then turn it off.
The second part of ntziolis answer is nearly correct but you don't need two sites or two application pools. You just need two file system folders that switch between being the physical folders for the site...if you're on a single server and not behind a load balancer or ARR.
If your sites were on a web server behind a load-balancer or ARR then having two different sites would make sense, you could route requests from one site to the other and round-robin on each deploy.
Obviously if there is a large amount of user generated content (uploaded files and the like) then you'd map a virtual directory in your site to a common location for this data.
In larger scale deployments where your app is running across (for example) a load-balanced environment you can do more sophisticated deployments.
For related questions please see:
How Do I deploy an application to IIS while that web application is running
Publishing/uploading new DLL to IIS: website goes down whilst uploading
Is smooth deployment possible with componentized ASP.NET MVC apps?
What is difference between application domain and application pool?
I have read many articles regarding these two terminology. but still unable to get proper understanding about them.
Please elaborate it with simple description.
Thanks
IIS process is w3wp;
Every application pool in IIS use it's own process;
AppPool1 uses process 3784, AppPool2 uses process 5044
Different applications in Asp.net will use different
AppDomain;
AppTest1 and AppTest2 are in different AppDomain, but in
the same process.
What's the point to use them?
Application pool and AppDomain , both of them can provide
isolations, but use different approaches. Application pool
use the process to isolate the applications which works
without .NET. But AppDomain is another isolation methods
provided by .NET.
If your server host thousands of web sites, you wont use
thousands of the application pool to isolate the web sites,
just because, too many processes running will kill the os.
However, sometime you need application pool. One of the
advantages for application pool is that you can config the
identity for application pool. Also you have more flexible
options to recycle the application pool. At least right now,
IIS didn't provide explicit options to recycle the appdomain.
An application pool is a group of one or more URLs of
different Web applications and Web sites. Any Web directory
or virtual directory can be assigned to an application pool.
Every application within an application pool shares the same
worker process executable, W3wp.exe, the worker process that
services one application pool is separated from the worker
process that services another [Like starting MS Word and
opening many word documents]. Each separate worker process
provides a process boundary so that when an application is
assigned to one application pool, problems in other
application pools do not affect the application. This
ensures that if a worker process fails, it does not affect
the applications running in other application pools. [i.e]
for Eg., If word document is having issue it should not
logically affect your Excel Sheet isn’t it.
application domain is a mechanism (similar to a process in
an operating system) used to isolate executed software
applications from one another so that they do not affect
each other. [i.e] opening of MS WORD doesn’t affect MS EXCEL
you can open and close both the applications any time since
there is no dependency between the applications. Each
application domain has its own virtual address space which
scopes the resources for the application domain using that
address space.
Thanks to this link
Edit 1
I am confused with the statement below, taken from What ASP.NET Programmers Should Know About Application Domains :
You’ve created two ASP.NET
applications on the same server, and
have not done any special
configuration. What is happening?
A single ASP.NET worker process will
host both of the ASP.NET applications.
On Windows XP and Windows 2000 this
process is named aspnet_wp.exe, and
the process runs under the security
context of the local ASPNET account.
On Windows 2003 the worker process has
the name w3wp.exe and runs under the
NETWORK SERVICE account by default.
He said that there is one worker process spawns 2 application domains--one application domain for each asp.net application.
But when I see the running processes as follows,
Image 1
Image 2
w3wp.exe is said as IIS Worker Process rather than application pool or application domain.
Questions:
Is application domain equal to application pool?
The confusing thing is in image 1. Why does Host Process Windows Service svchost.exe spawns 2 IIS Worker Process w3wp.exe? In my understanding, a process can only contain application domains, not other processes.
Application domain aka AppDomain (its class representation) is an encapsulated environment inside a .NET runtime where assemblies are loaded and running.
Usually there is one AppDomain/Application domain per managed process but can be more. Here the article refers to 2 AppDomains inside the same w3wp3.exe process.
You can see number of AppDomains loaded in any process using perfmon.exe
To answer your question, usually one AppDomain is created per one AppPool. But it is possible to load extra AppDomains manually in the AppPool by the application - but that would be very uncommon.
Update
I think you are using Process Explorer of the Sysinternals. Ignore the way it shows the tree structure in there, it only illustrates which process has spawned other processes. In fact it shows most processes underneath explorer since explorer has been used to load it.
Also SVCHOST.exe is an unmanaged executable and although it can host CLR and load AppDomains, it normally does not do that.
Scenario: I've an n-Tier enterprise ASP.NET application deployed using Web Deployment Projects. All tiers produce independent assemblies that is consumed by the ASP.NET application.
Problem: When I run the app. for the first time after deployment it takes lot of time to load dependent assemblies in memory. But once loaded its lighting fast app. In case if there are no users accessing the app, IIS unloads the assemblies from the memory and when a user tried to access the app on a later instance it goes on loading all the assemblies once again taking the same amount of time to load as it takes to do so for the first time.
I'm looking for a solution that enables me to keep my assemblies loaded into memory persistently overriding the volatile nature of assemblies towards memory residency.
Or any other solution that lets my users happily use the app resolving the mentioned problem.
In IIS 6, go to the Application Pools section, and right-click > Properties on the pool which hosts the ASP.NET application in question. Go to the Performance tab and uncheck "Shutdown worker processes after being idle for:"
In IIS 7, go to the Connections pane and find Application Pools, and select Advanced Settings for the pool which hosts your application. Find the "Idle Timeout" property and set it to "0" (this disables it).
The default is 20 minutes of inactivity. By unchecking the box, once your AppDomain is loaded by the worker process, it will never die (unless you kill the process or something of course). By default, IIS will recycle the process when it reaches some limit, such as a memory cap, but it will also start a new one and "phase over" all incoming requests until the old one is unused, so as to minimize disruption.
I've also written a small c# class which will keep your ASP.NET application alive (alternate archived version) under normal circumstances. Since it runs within the application, obviously it can't stop IIS or anything else from explicitly killing the process, but it will keep the application "hot", e.g. the app will never go idle long enough for IIS to decide to shut it off.
If you do not have direct control over your IIS configuration (shared host, for example) your best bet is to have a small application running on a separate system - say, an always-on workstation - which hits your site every x minutes to keep the application pool from timing out. Nothing fancy - a simple WebRequest and a while() loop in a console application will do.
One of the advantages of ASP .net is the posibility to create static (shared) instances of objects.
To avoid the necessity of an external process you can create an static timer in (per example) global.asax which calls for a page on the domain with a simple WebRequest. On this way the site keeps alive himself until a manual reset of the pool is done.
I wrote a little C# console application that keeps my 4 sites alive every 10 mins via windows task scheduler. Life is once again good. We do not run the app from 2-5am just so the serves can do any cleanups of memory, if it even matters. for our sites there is rarely anyone on at those hours anyway.