HTTP Error 503. The service is unavailable

Question

I'm struggling to setup the environment in IIS8, I searched a lot but couldn't find a right solution.

I checked the error logs, but no idea.

C:\Windows\System32\LogFiles\HTTPERR

1. 2013-10-09 09:28:39 192.168.43.205 60172 192.168.43.205 80 HTTP/1.1 GET / 503 2 AppOffline qa.hti.local
2. 2013-10-09 09:28:39 192.168.43.205 60192 192.168.43.205 80 HTTP/1.1 GET /favicon.ico 503 2 AppOffline qa.hti.local

Then in Event Viewer:

WARNINGS:

1. A listener channel for protocol 'http' in worker process '11188' serving application pool 'qa.hti.local' reported a listener channel failure. The data field contains the error number.
2. A listener channel for protocol 'http' in worker process '7492' serving application pool 'qa.hti.local' reported a listener channel failure. The data field contains the error number.
3. A listener channel for protocol 'http' in worker process '9088' serving application pool 'qa.hti.local' reported a listener channel failure. The data field contains the error number.
4. A listener channel for protocol 'http' in worker process '9964' serving application pool 'qa.hti.local' reported a listener channel failure. The data field contains the error number.
5. A listener channel for protocol 'http' in worker process '7716' serving application pool 'qa.hti.local' reported a listener channel failure. The data field contains the error number.

I don't understand what the warning means.

ERROR: Application pool 'qa.hti.local' is being automatically disabled due to a series of failures in the process(es) serving that application pool.

Note: I learned that consecutive 5 failures leads to APP Pool crash, and this can increased. I also tried increasing this but no success.

OS: Windows server 2012
IIS Version: 8

Please share your thoughts.

Answer 1

FYI -

I'd like to add that I too am experiencing this, and have a vested interest in a solution. That said, my spec's seem to match yours, however I'd like to know about your server load.

OS: Windows Server 2012 Standard

IIS: IIS 8

Application Stack: .NET 4.0

The one thing we notice, is this problem does NOT happen when there isn't any load. We can hit the server all day with just 5 or 10 users, but the second the server comes into production with the others in the farm, we get intermittent and random 503 issues.

How many clients/users are connecting to your server?

Have you tried the following:

Application Pool Advanced Settings:

Queue Length: Default is 1000, try setting it to 5000 if you have an x64 system, and more than about 4GB of RAM

NOTE ON QUEUE LENGTH: On the Queue Length, you might actually see errors in the HTTP System Error logs that correspond with the App Pools dying. If you do, this might be a fix.

Private Bytes Memory: Are you specifying a setting here, or is your value "0" (Means unlimited).

let us know your findings, and if the Queue Length works for you.

Let us know on those

Answer 2

We resolved this by correlating the application and system event logs. There was a module listed in the applicationhost.config or web.config that was not on the file system. The application event log called out the file path. Once I added the module back to the server, the app pool started.

Answer 3

Does this server have any Remote Desktop / TS Gateway functionality on it? There appears to be a known issue with running 32 bit IIS applications on the same server that TS Gateway is running on.

To get round this you can set your app pool to run 64 bit (if you're using pure .NET code this should just work fine).

Additionally, there could be a module that hasn't installed properly. This blog post is relatively old but shows similar symptoms to yours and the solution is to see if the event log shows any other erroring components and to resolve those first.

Answer 4

I came across this question as I was experiencing a similar issue and searching for a solution.

My problem specifically had to do with our IIS shared configuration. We had enabled a feature in IIS on one of the servers (Http Redirect) that was not installed on any of the others so the server 'features' were out of sync with all the servers.

I was able to resolve the issue by uninstalling the new addition on the first server so it was back to matching the others. An IIS reset later and the AppPools were no longer going down and all was back to normal.

So if you are using IIS Shared Configuration and the IIS is creating 'Service Unavailable' errors and the AppPools are going down, this can be a symptom of the system configuration being out of synch which is corrupting the shared configuration. Hopefully this post will help someone find the solution faster than I was able to.