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HOWTO: Diagnose one cause of 503 Service Unavailable on IIS6

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I recently got this question about encountering a 503 Service Unavailable error on 64bit Windows. The author chose to uninstall .NET Framework 1.1 as the resolution, but I think there are some better alternatives...

Question:

I was delighted to run across your treatment of ISAPI Filter 'service unavailable' woes; it gave me the courage to try to get to the bottom of my particular problem. You might (or might not) want to post something of the solution I found in my own situation:

On Windows XP x64 happily running IIS6, the installation of the .NET Framework 1.1 kills the IIS6 with the 'service unavailable' message returned; uninstalling the .NET Framework returned things to the status quo ante.

I am trying to find the blog you wrote on the 503 error and cannot find it. The google link goes to a page that does not have the information on it. I am trying to get Win XP x64 to work with VS 2003 ASP.net 1.1 and I am getting the 503 error and I cannot find any information on what to do about it. Any help would be appreciated.

Answer:

Actually, I think your situation has a better solution than uninstalling .NET Framework 1.1. If my guess is right, you should be able to run .NET Framework 1.1 on 64 bit IIS6.

If you check your Event Log entries, you will likely find several of the following entry, followed by another entry declaring that the Application Pool is being disabled. This disabling is what causes the 503 Service Unavailable to be returned.

 Event Type: Error 
Event Source: W3SVC-WP 
Event Category: None 
Event ID: 2268 

Description: 
Could not load all ISAPI filters for site/service. Therefore startup aborted. 
Data: 0000: c1 00 00 00

The reason why you are getting this event is straight forward:

  • On 64bit Windows, the "bitness" (i.e. 32bit or 64bit) of a process must match the bitness of the DLLs loaded by that process. In other words, a 64bit EXE can only load 64bit DLLs, and 32bit EXE can only load 32bit DLLs.
  • By default, IIS6 on 64bit Windows runs with 64bit W3WP.EXE worker processes
  • .NET Framework 1.1 has ASP.Net implemented through 32bit ISAPI DLLs.

What is happening when you install .NET Framework 1.1 on IIS6 on 64bit Windows is that while IIS6 runs W3WP.EXE as 64bit, you are configuring it to load some 32bit ISAPI DLLs. This does not work and leads to the event log entry. Since the ISAPI DLLs are loaded for every request, this failure immediately happens again and again, thus triggering the "Rapid Fail Protection" health monitoring check of IIS6. This leads to this Application Pool being taken offline and a 503 Service Unavailable response being sent.

One way to fix this issue is to:

  1. Change IIS6 run W3WP.EXE as 32bit
  2. *** IMPORTANT *** Then restart the Application Pool that returns the 503 error since it is stopped. You cannot fix any 503 error without restarting the Application Pool.

Changing IIS6 to run W3WP.EXE as 32bit allows the 32bit ISAPI DLLs installed by .NET Framework 1.1 for ASP.NET to load and run inside of it. This is done by running the following commandline:

 CSCRIPT %SYSTEMDRIVE%\Inetpub\AdminScripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 1

This command switches IIS6 into running WOW64 (i.e. 32bit compatibility) mode on 64bit Windows on-the-fly so that IIS6 can immediately run 32bit ISAPI DLLs... unless that Application Pool is ALREADY returning 503 errors, in which case you MUST restart the Application Pool to have the bitness switch take effect. It makes sense because a 503 error means the Application Pool is offline and not running, so you must restart it to have setting changes take effect.

You can do this by either:

  • Restarting the Application Pool in question

  • Restarting IIS

     NET STOP W3SVC /y & NET START W3SVC

  • Reboot the server

     SHUTDOWN -r -t 0

Now, I cannot guarantee that this works for you because you may have other applications that must run as 64bit, in which case you have a conflicting need to simultaneously run 32bit and 64bit code in IIS6, which is not allowed.

See KB 895976 for more details.

I am also going to write up a more complete explanation of WOW64 and running 32bit applications on IIS6 in Windows Server 2003 SP1 (same codebase as Windows XP 64bit Edition) in the near future. I have answered this question to many people for the past year now, and I want to answer it once and for all. :-)

//David

Comments

  • Anonymous
    October 22, 2005
    Hi. That script didnt make it work for me. Same error. :(

  • Anonymous
    October 22, 2005
    Adelino - Is your 503 actually caused by what I describe? Because the resolution I describe is specific to that cause, and it definitely works because it addresses the fundamental issue.

    Of course, with bitness issues, it is possible for many, many variations and no single approach will work. You just have to know what you are configuring.

    If you cannot get it working, you may want to consider moving back to x86 because you definitely need to learn and understand x64 in order to use it correctly, especially during this 32-64bit transition phase...

    //David

  • Anonymous
    November 15, 2005
    Hello folks, well I had the same problem and the above mentioned fix did not work me. After digging around you must download and install the Microsoft .NET Framework Version 2.0 Redistributable Package (x64). This also updates IIS 6.0.
    After this update I have no problems running VS 2003 and any .NET projects under XP64.
    The URL for the download is here:
    http://www.microsoft.com/downloads/thankyou.aspx?familyId=b44a0000-acf8-4fa1-affb-40e78d788b00&displayLang=en&oRef=

    I hope this helps, good luck.

  • Anonymous
    November 15, 2005
    Eric-Goz - I suspect the reason it did not work for you is because when you changed bitness to 32bit, you had other ISAPIs that depended on (or is configured) to being 64bit. But, that is an expected conflict, as I mentioned in the blog entry.

    When you run the native x64 redistributable, everything runs as 64bit, so everything is happy.

    FYI: .Net Framework redistributable does NOT update IIS6.

    //David

  • Anonymous
    December 02, 2005
    I wanted to report that this fix worked great for me but <b>NEEDED A REBOOT</b>.

    I'm now running Microsoft Visual Studio.NET 2003 without a glitch (debugging and all) with Framework 1.1.

  • Anonymous
    December 02, 2005
    Guillaume - Glad to hear that. However, the fix itself should not require a reboot to take effect:
    - Toggling IIS bitness takes effect immediately
    - To rescue an Application Pool that went into 503 Service Available, just restart the Application Pool from the IIS Manager UI

    So, recovery from this issue should be a matter of changing one configuration property, restarting the afflicted Application Pool(s), and things are good to go.

    //David

  • Anonymous
    January 06, 2006
    David:

    Your fix works perfectly. You definitely must stop and restart the Application Pool (not recycle) for the change to take effect and lose the 503 Error.

    Dirk

  • Anonymous
    March 13, 2006
    Strange. I have answered this question recently on how to diagnose a common cause of &quot;503 Service Unavailable&quot;...

  • Anonymous
    March 19, 2006
    One of the cooler but definitely unsung feature of the IIS7 Server Core is PreConditions. So, that's...

  • Anonymous
    March 31, 2006
    Dave:
    Thanks for a good solution. I was running Win2k3 x64 with both .NET 1.1 and 2.0, and had the server automatically download and install MS fixes. Big mistake! The fix for 1.1 broke my 2 code!

    Solution: removed 1.1 and re-installed from distribution 2.

    Shame on Microsoft for issuing "patches" that break the existing software (remember XP SP2?)

    Again, thank alot,
    DVJ

  • Anonymous
    March 31, 2006
    The comment has been removed

  • Anonymous
    May 05, 2006
    The following links to .NET resources have been collated over time with the assistance of colleagues.&amp;nbsp;...

  • Anonymous
    May 13, 2006
    Your solution resolved my inability to run VS2005 on x64 too.    Everything was fine until I installed Pinnacle that required .Net1.1.    Thanks.

  • Anonymous
    May 29, 2006
    The comment has been removed

  • Anonymous
    June 16, 2006
    Another 10K entry... yes, WOW64 and 503 are truly confusing.

    //David

  • Anonymous
    June 26, 2006
    Hey i'm running Windows Vista with the same problem.(32 bit) Is there a way to fix this?

  • Anonymous
    June 26, 2006
    Hunter - without more information, your issue cannot be diagnosed nor fixed.

    I suggest that you ask your questions on IIS-related newsgroups to focus on determining what is actually wrong. You can access it via web-based reader:
     http://www.microsoft.com/windowsserver2003/community/centers/iis/default.mspx
    Or NNTP News Reader on msnews.microsoft.com server for newsgroup:
     microsoft.public.inetserver.iis.

    //David

  • Anonymous
    July 07, 2006
    the correct link is
    http://www.microsoft.com/downloads/details.aspx?familyid=b44a0000-acf8-4fa1-affb-40e78d788b00&displaylang=en

  • Anonymous
    July 07, 2006
    Thanks! This fixed the error and no reboot required!

  • Anonymous
    September 19, 2006
    My case of 503 problem is little bit different. On production we have depolyed applications developed in Framework 1.1 and its working fine since more than a year When we changed a piece of code in application and re released the application, after two days of successfull run it started getting 503 error. In HTTPError log there are entries mentioning connection pool abandoned. When application is reverted back with the older(which was running fine) version it again started working fine and there is no 503. This problem is coming only when we deployed new version of our application that too new versions runs perfectly for few days. We have done the rigorus code analysis also to ensure there is no infinite loop or memory leak exists.

    I accept different reasons of this 503 error but it must behave uniformely. Why it is coming only when new version is deployed.

    In both the version nomrally the simultaneous users accessing sytem are crossed 80,000 some times

    Any suggestions will be welcomed....

  • Anonymous
    September 19, 2006
    My case of 503 problem is little bit different. On production we have depolyed applications developed in Framework 1.1 and its working fine since more than a year When we changed a piece of code in application and re released the application, after two days of successfull run it started getting 503 error. In HTTPError log there are entries mentioning connection pool abandoned. When application is reverted back with the older(which was running fine) version it again started working fine and there is no 503. This problem is coming only when we deployed new version of our application that too new versions runs perfectly for few days. We have done the rigorus code analysis also to ensure there is no infinite loop or memory leak exists.

    I accept different reasons of this 503 error but it must behave uniformely. Why it is coming only when new version is deployed.

    In both the version nomrally the simultaneous users accessing sytem are crossed 80,000 some times

    Any suggestions will be welcomed....

  • Anonymous
    September 19, 2006
    My case of 503 problem is little bit different. On production we have depolyed applications developed in Framework 1.1 and its working fine since more than a year When we changed a piece of code in application and re released the application, after two days of successfull run it started getting 503 error. In HTTPError log there are entries mentioning connection pool abandoned. When application is reverted back with the older(which was running fine) version it again started working fine and there is no 503. This problem is coming only when we deployed new version of our application that too new versions runs perfectly for few days. We have done the rigorus code analysis also to ensure there is no infinite loop or memory leak exists.

    I accept different reasons of this 503 error but it must behave uniformely. Why it is coming only when new version is deployed.

    In both the version nomrally the simultaneous users accessing sytem are crossed 80,000 some times

    Any suggestions will be welcomed....

  • Anonymous
    June 04, 2007
    Hi,      I also received 503 problem and log file (C:WINDOWSsystem32LogFilesHTTPERRhttperr1.log) is as follows: #Software: Microsoft HTTP API 1.0 #Version: 1.0 #Date: 2007-06-05 04:33:50 #Fields: date time c-ip c-port s-ip s-port cs-version cs-method cs-uri sc-status s-siteid s-reason s-queuename 2007-06-05 04:33:50 13.205.105.18 1042 13.205.105.18 80 HTTP/1.1 GET / 503 1 AppOffline DefaultAppPool 2007-06-05 04:33:57 13.205.105.18 1043 13.205.105.18 80 HTTP/1.1 GET /certsrv/ 503 1 AppOffline DefaultAppPool 2007-06-05 04:34:18 127.0.0.1 1044 127.0.0.1 80 HTTP/1.1 GET /certsrv/default.asp 503 1 AppOffline DefaultAppPool 2007-06-05 04:34:46 127.0.0.1 1045 127.0.0.1 80 HTTP/1.1 GET /certsrv/default.asp 503 1 AppOffline DefaultAppPool 2007-06-05 04:34:46 13.205.105.18 1046 13.205.105.18 80 HTTP/1.1 GET / 503 1 AppOffline DefaultAppPool 2007-06-05 04:34:50 13.205.105.18 1047 13.205.105.18 80 HTTP/1.1 GET /certsrv 503 1 AppOffline DefaultAppPool 2007-06-05 04:35:32 13.205.105.18 1049 13.205.105.18 80 HTTP/1.1 GET /certsrv 503 1 AppOffline DefaultAppPool 2007-06-05 04:36:31 127.0.0.1 1051 127.0.0.1 80 HTTP/1.1 GET / 503 1 AppOffline DefaultAppPool 2007-06-05 04:37:21 127.0.0.1 1052 127.0.0.1 2077 HTTP/1.1 GET / - 2 Connection_Dropped MSSharePointAppPool 2007-06-05 04:37:52 127.0.0.1 1053 127.0.0.1 80 HTTP/1.1 GET / 503 1 AppOffline DefaultAppPool 2007-06-05 04:38:52 127.0.0.1 1054 127.0.0.1 2077 HTTP/1.1 GET / - 2 Connection_Dropped MSSharePointAppPool 2007-06-05 04:45:44 127.0.0.1 1058 127.0.0.1 80 HTTP/1.1 GET /certsrv/ 503 1 AppOffline DefaultAppPool 2007-06-05 04:47:58 127.0.0.1 1060 127.0.0.1 80 HTTP/1.1 GET /certsrv/ 503 1 AppOffline DefaultAppPool 2007-06-05 04:47:59 127.0.0.1 1061 127.0.0.1 80 HTTP/1.1 GET /certsrv/ 503 1 AppOffline DefaultAppPool 2007-06-05 04:48:00 127.0.0.1 1062 127.0.0.1 80 HTTP/1.1 GET /certsrv/ 503 1 AppOffline DefaultAppPool 2007-06-05 04:49:57 127.0.0.1 1064 127.0.0.1 80 HTTP/1.1 GET /certsrv/ 503 1 AppOffline DefaultAppPool #Software: Microsoft HTTP API 1.0 I installed the Windows server 2003 (with sp1) in standard installation. I installed IIS server and then certificate services. Restarted the system and tries to connect http:\localhostcertsrv, but in vein.  Finally a quick and clever notice is caught.  For simplicity i did the dump in harddisk to increase speed of installation and as a backup, so that i did not require to insert Windows server cd everytime. Also, I did not require R2 so i didnt installed it. But when installing IIS services from control panel, i am asked to provide some file , i browsed to cd location but some file is not there, so alternatively these file found in R2 cd dump and picked up from there (!!!!NOTE NOTE NOTE ....root cause) . So when i tries to run http:\localhostcertsrv, i got service unavailable error. Everything looks fine but nothing +ve happens. After so many tries , i uninstalled the IIS & Certificate. And when installed again , i insert the CD in drive and provide file from there (Voila, now the file it is not able to locate from hardisk(so provided from R2 Dump) is in CD !!!). AND EVERYTHING WORKS FINE THEN..... :) Anil

  • Anonymous
    June 26, 2007
    At first, I tried everything that was mentioned above, and it didn't work for me either.  I was trying to install CF as a Multiserver Configuration.   What worked was when I installed CF as a Server Configuration. Thanks David for your blog!

  • Anonymous
    July 31, 2007
    I was also having a problem with running CF on the 64 bit version of windows 2003.  The script by itself did not work (although it does have to be run) What got it going for me was the link that Eric-Goz suggested. I downloaded it, ran it, selected rebuild, rebooted and now all is well. Thanks guys P.S. Here's the link again http://www.microsoft.com/downloads/thankyou.aspx?familyId=b44a0000-acf8-4fa1-affb-40e78d788b00&displayLang=en&oRef=

  • Anonymous
    January 07, 2008
    The version of RPC over HTTP proxy that ships with x64 version of server 2003 has 64 bit DLL's, and thus breaks IIS running in 32 bit mode. Would it be possible to copy the 32 bit DLL's for RPC proxy from a 32 bit server 2003 install and overwirte the 64 bit ones, or would that be a bad idea? Thanks in advance...

  • Anonymous
    January 07, 2008
    The comment has been removed

  • Anonymous
    June 01, 2008
    The comment has been removed

  • Anonymous
    June 01, 2008
    The comment has been removed

  • Anonymous
    July 16, 2008
    I think this fix should not be recommended. When you say it is a better solution than uninstalling the incompatible .NET 1.1, i don't think this is the case. While the fix may certainly work to get IIS running in 32bit mode on a 64 bit install, and allow the 32bit .NET 1.1 to work, imagine the future incompatibilities when someone comes along and finds this completely non standard setup. It would be a maintenance nightmare... you do mention this briefly in the blog post, but i think you should emphasize to only do this if you really need to run the 32bit mode.

  • Anonymous
    July 17, 2008
    c8to - I agree with you that running purely 64bit is preferred and cleaner approach. However, running 32bit .Net 1.1 on 64bit Windows is also supported by Microsoft because customers request/require it. It is a case-by-cases basis. In this blog entry, I am simply describing what was going on with a misconfiguration. I have insufficient information to determine nor advise any case-by-case recommendation. //David

  • Anonymous
    November 15, 2008
    The comment has been removed

  • Anonymous
    November 29, 2008
    EASY SOLUTION: IIS7 -> APPLICATION POOLS -> ASP.NET 1,1 -> SET APPLICATION POOL DEFAULTS -> ENABLE 32-BIT APPLICATIONS -> TRUE. THIS WILL WORK!!!!

  • Anonymous
    November 29, 2008
    CMZK - yes, that is one possible solution, but only for a certain problem, and not all 503s. You need to specify to which problem your solution is for... //David

  • Anonymous
    March 02, 2009
    I followed this procedure : IIS7 -> APPLICATION POOLS -> ASP.NET 1,1 -> SET APPLICATION POOL DEFAULTS -> ENABLE 32-BIT APPLICATIONS -> TRUE Even after doing this change also the application is getting stopped after some time.

  • Anonymous
    December 07, 2009
    I found another method that works for IIS 7.0 and helped me at http://blog.evonet.com.au/post/2008/08/22/503-service-unavailable-errors-when-IIS-running-in-32-bit-mode-on-64-bit-Windows-Server-2008.aspx The problem was the access ODBC driver.

  • Anonymous
    January 31, 2010
    I am also facing this 503 service unavailable error. WHen I remove IIRF filter then error is  gone. coul dthis error be related to IIRF filter