IIS and Static content?

Question

According to Ultra-Fast ASP.NET: Chapter 3 - Caching:

Files that the browser retrieves from the server should be stored in the browser’s cache as long as possible to help minimize server round-trips.

• But how does IIS know what a static content actually is and is not?

  Is it just images, CSS, JS and not ASPX, ashx...?

  Where can I see in IIS what is already considered to be static and what is not ?

• What about the scenario where a page has been declared with <%@ OutputCache header (without location)? Are the images, CSS and JS source files inside of it also being output cached with the same properties?

• As a best practice, I should set one year into the future as the maximum expiration time. I should use that as the default for all static content on the site

So I did this :

But later, after pressing OK, I can't find any summary menu which shows me: to whom I already put a response header (in this case: the css folder).

Currently, in order to see that css folder has been applied with response headers - I have to go to the css folder again --> Http Response Header-->Set Common Headers --> and then I see it. It isn't written in the web.config.

But if I do it for a file (Login.aspx for example): I do see it in web.config:

<configuration>
    <location path="Login.aspx">
        <system.webServer>
            <staticContent>
                <clientCache cacheControlMode="UseExpires" cacheControlMaxAge="1.00:00:00" httpExpires="Fri, 15 Feb 2013 00:00:00 GMT" />
            </staticContent>
        </system.webServer>
    </location>
</configuration>

Illdisposed

while using both UseExpires and UseMaxAge as done here, i get 500 internal server error, did your solution work, can we use both ? because i see stack overflow do that for their css and js etc but dont know how ? – Stumpf

Answer 1

I understand your situation. Sometime its confusing how IIS handles a file. Its also different for IIS 6 vs IIS 7 and different for Classic App Pools and Integrated mode app pools. My experience is mostly with Integrated App Pools on IIS 7.5, so thats the environment I can comment on most accurately.

First Question

But how does IIS knows what is actually a static content and what is not?

Is it just images , css , js and not ASPX , ashx...?

Where can I see in the IIS what is already considered to be static and what not ?

You can inspect the list of file handlers in IIS by navigating to your website and then click 'Handler Mappings'. By default these are inherited from the .Net base web.config which is in a different location depending on your .Net framework version.

• C:\Windows\Microsoft.NET\Framework\v2.0.50727\CONFIG\web.config
• C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config\web.config

If a file being requested isn't already explicitly mapped to another handler it falls to a catch all handler (*) as the last option (System.Web.DefaultHttpHandler) which determines if it is a static file or a directory browsing request. So Static files are simply files not bound to another handler already. For example you'll see that *.aspx is already mapped to System.Web.UI.PageHandlerFactory prior to this default handler. So its going to be processed by that handler and not be considered a static file. If you removed that mapping you could technically serve *.aspx as a static file if you really wanted to (just for proof of how it works).

But you can also explicitly list a file type as a static file by adding an entry in your web.config's httpHandlers section mapping the file extensions to System.Web.StaticFileHandler in IIS. For example:

<configuration>
  <system.webServer>
    <handlers>
      <add name="StaticHandler" verb="*" path="*.zip" type="System.Web.StaticFileHandler" preCondition="integratedMode" />
    </handlers>
  </system.webServer>
</configuration>

This example is using the <system.webServer> config section, so its for an App Pool running in Integrated Mode.

Second Question

What about the scenario where a page has been declared with <%@ OutputCache header(without location) . does the images,css,js src files inside of it , are also being output cached with the same properties?

No. Because the page is being server as a separate request (maybe even by a separate handler) it can have totally different cache headers/hints. The host page and the resources it may use are not related from a caching perspective.

In fact you may even want to have a shorter cache period for *.html and a longer cache period for *.jpg or *.png? Something to consider.

Third Question

As a best prcatice , I should set one year into the future as the maximum expiration time.I should use that as the default for all static content on the site

Hmm... I might not go as far as one year. How about one month? I would set a global policy like this:

<configuration>
  <system.webServer>
    <staticContent>
      <!-- Set expire headers to 30 days for static content-->
      <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="30.00:00:00" />
    </staticContent>
  </system.webServer>
</configuration>

This is the same as the sample you showed above, but is not inside a <location> element, instead it is right in the root <configuration> element so it is the default policy. Again this is for an App Pool running in Integrated Mode. Sometimes you also need to turn on:

<configuration>
    <system.webServer>
        <modules runAllManagedModulesForAllRequests="true">
            <!-- stuff -->
        </modules>
    </system.webServer>
<system.webServer>

This just makes sure that static files are processed through the managed static file handler which respects the above configuration elements.

Edit to Address Comments

The documentation for the configuration dialog you posted above is located here: Configure the HTTP Expires Response Header (IIS 7)

Apparently these settings are saved in C:\Windows\System32\inetsrv\config\applicationHost.config

I do not have IIS7 and personally develop on IIS 7.5 now. So please post a comment if you can verify this location is accurate!

Chud

What about the css folder in my pic above ? Where can i see it already cached ? – Illdisposed

@RoyiNamir I thought you would see my edit at the bottom of the question which I added in response. I can't test because I don't have IIS 7, but it appears the file is normally located C:\Windows\System32\inetsrv\config\applicationHost.config. Open that file and search for the settings you are looking for. Again I can't confirm IIS7, so please post a comment here if this is successful! – Chud

No . it does not show me that CSS is cached.Thanks for reply. – Illdisposed

Can you elaborate on the bit about runAllManagedModulesForAllRequests="true"? You said that sometimes you need to turn it on, but how do you determine when? – Hollins

while using both UseExpires and UseMaxAge as done here, i get 500 internal server error, can we use both ? because i see stack overflow do that for their css and js etc but don't know how ? – Stumpf

What is the purpose of specifying a System.Web.StaticFileHandler for a file extension when all static files that are not mapped to a certain handler, like pdf, txt, csv, png, jpg ... will finally be mapped to the StaticFileHandler anyway ? What is the difference when running this handler with precondition integratedMode vs. managedHandler ? – Conspire

Answer 2

1. The static content is the one that IIS is read and send to the browser with out any processing. There you can setup IIS to include some Cache-Control Header to cache it on clients browser computers.
2. You can do that ether by direct setup IIS, ether by commands on web.config as you say. The commands that you add on web.config and concern the IIS, did not have to do with asp.net it self, but the IIS, and IIS saves his configuration on a different file, so when you change that cache control headers direct on IIS you do not see them on web.config.
3. Now for the static content like images, CSS, JavaScript, and other similar files they say that you can follow the "never expire" policy by adding 10 years expire.
4. The issue here is that if you can not change the content of the static file, if for example you cache a javascript file with 10 years, and you make a small change on it, then you need ether to change the file name, ether to add some parameter at the end of it.
5. Now the <%@ OutputCache on a control is referred to the server cache and not to the client, and what is actually do is to cache the render of the control on the server so the next time you ask it to not lose time to renders it again but read it from cache - is still send it to the browser.

And you can also read this answer for some more: What are difference between IIS (Dynamic and Static) cache,OutPutCache and browser cache

Debarath

Thanks. regarding #1 : So the declaration of static and ntot static is a runtime decision of the iis ? does he remembers what resources were already marked as static from the last request ? regarding #2 the CSS folder in my example were not saved in the web.config ! how can I see that the css folder has been set with CustomHttpHeaders? regarding #5 I said I didn't set any location so i think it would be private by default.(IMHO) which is the browser.(it will be great if you can answer my 3'rd question as well). – Illdisposed

@RoyiNamir The iis is saves all the setup to a file that is locked all time and is good to avoid it - I thing that is the C:\Windows\System32\inetsrv\config\applicationHost.config but you can search on the internet for more informations – Debarath

@RoyiNamir I do not know to answer for the location to tell you the truth I am not sure what you talk about. In any case you can read the header of your static content on the browser to see what your iis sends. – Debarath

@RoyiNamir I say you that this settings are for IIS, so do not wait to see them on web.config. Now when you place them on web.config is actually for giving commands to IIS what to do. – Debarath

Aristos if i dont set any location , it could be cached on browser or server.msdn.microsoft.com/en-us/library/hdxfb6cy(v=vs.71).aspx The default is Any – Illdisposed

@RoyiNamir This is client header command, have nothing to do with the server, so its for browser only. – Debarath

let us continue this discussion in chat – Illdisposed

location= "server" is implemented at the ResolveRequestCache in the HTTP MODULE. I don't understand why you say it is not in the server. only when you write Location=Private - it is saved in browser. It would be much better if you kindly go to the chat room. – Illdisposed